A METHOD FOR EFFICIENT ELECTROCATALYTIC SYNTHESIS OF PURE LIQUID PRODUCT SOLUTIONS INCLUDING H2O2, OXYGENATES, AMMONIA, AND SO ON

A porous solid electrolyte electrosynthesis cell and corresponding related process for the direct synthesis of high purity liquid products wherein the electrosynthesis cell comprises a cathode compartment including a cathode electrode comprising a gas diffusion layer loaded with a selective reduction reaction electrocatalyst for specific reduction reactions. The electrosynthesis cell further includes an anode compartment including an anode electrode comprising a gas diffusion layer loaded with a catalyst for oxidation reactions; and a solid electrolyte compartment comprising a porous solid electrolyte; a cation exchange membrane; and an anion exchange membrane; (or two cation exchange membranes) wherein the solid electrolyte compartment is separated from the cathode and the anode by the anion exchange membrane and the cation exchange membrane (or by the two cation exchange membranes).

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Description
CROSS-REFERENCE TO RELATED APPLICATIONS

This Application claims priority from U.S. Provisional Application No. 62/874,176, which was filed in the United States of America on Jul. 15, 2019.

BACKGROUND

Hydrogen peroxide (H2O2) is a nexus chemical for a variety of industries, and it is currently produced through an indirect, energy-demanding, and waste-intensive anthraquinone process. This traditional method usually generates H2O2 mixtures with concentrations of 1-2 wt. %, followed with further purifications and distillations, where significant costs adds up, to reach concentrated pure H2O2 solutions for commercial use. However, this process requires centralized infrastructures and thus relies heavily on transportation and storage of bulk H2O2 solutions, which are unstable and hazardous.

The direct synthesis of H2O2 from hydrogen (H2) and oxygen (O2) mixture (FIG. 1A) provides an alternative route for small-scale on-site generation. Exciting progresses have been made in developing selective catalysts over the past decade, such as the palladium-tin catalyst with high selectivity (>95%) and productivity (61 mol kgcat-1 h-1) towards H2O2. However, due to the wide range of H2 flammability limits, one big challenge of this direct synthesis route is the inherent hazard associated with mixing high-pressure H2 and O2. Thus, in practice, H2 feedstock needs to be heavily diluted using CO2 or N2 carrier gas, significantly lowering the yields of H2O2. In addition, the use of methanol in solvents can lead to extra cost in product separation for pure H2O2 aqueous solutions.

Different from the direct synthesis, where O2 and H2 are mixed and catalyzed on the same catalytic surface, the direct electrosynthesis of H2O2 can decouple the H2/O2 redox into two half-cell reactions (alkaline conditions for example):


2e-O2 reduction reaction (2e-ORR): O2+H2O+2e−→HO2−+OH−;   (Eq. 1)


H2 (HOR): H2+2OH−-2e−→2H2O.   (Eq. 2)

Advantages of this electrochemical route are obvious, including 1) O2 and H2 can be completely separated without safety issue, and fed with high purity for high reaction rates; 2) different catalysts can be designed separately for 2e-ORR and HOR/OER, with each half-cell reaction optimized; 3) the synthesis can be operated under ambient conditions for renewable and on-site H2O2 generation; and 4) the H2/O2 redox couple could even output electricity during H2O2 synthesis. Although there have been selective catalysts such as noble metals or carbon materials developed for the 2e-ORR pathway, the generated H2O2 products were usually mixed with solutes in traditional liquid electrolytes ranging from acidic to alkaline solutions. Extra separation processes to recover pure H2O2 solutions for use were therefore required. Other designs including using deionized water (DI water), or polymer electrolyte membrane as ion conducting electrolyte were rarely proposed for obtaining pure H2O2 solutions, but they generally suffered from low reaction rates, product concentrations, or Faradaic Efficiencies (FEs).

Embodiments herein relate to an alternative and highly efficient concept that employs a porous solid electrolyte electrolytic cell comprised of a cathodic catalyst, an anodic catalyst, ion exchange membranes, and solid electrolyte wherein a porous solid electrolyte design is used to realize the direct electrosynthesis of pure H2O2 as well as many other liquid product solutions. Depending on the pure liquid product to be produced, the cathodic catalyst could be 2e oxygen reduction reaction catalyst (such as oxidized carbon) to generate pure H2O2 solutions, or CO2/CO reduction catalyst for pure oxygenates solutions, or N2/NO3/NO2 reduction catalyst for pure N species solutions, and so on. Solid electrolytes can also be replaced with the corresponding liquid products if high ionic conductivity can be maintained.

In one aspect, embodiments disclosed herein generally relate to a porous solid electrolyte electrosynthesis cell for direct synthesis of high purity liquid products wherein the electrosynthesis cell comprises a cathode compartment including a cathode electrode comprising a gas diffusion layer loaded with a selective reduction reaction electrocatalyst for specific reduction reactions wherein the reduction reactions comprise oxygen reduction reactions, CO2 reduction reactions, CO reduction reactions, N2 reduction reactions, nitrate reduction reactions and nitrite reduction reactions. The electrosynthesis cell further includes an anode compartment including an anode electrode comprising a gas diffusion layer loaded with a catalyst for oxidation reactions; a solid electrolyte compartment comprising a porous solid electrolyte; a cation exchange membrane; and an anion exchange membrane; wherein the solid electrolyte compartment is separated from the cathode and the anode by the anion exchange membrane and/or the cation exchange membrane.

In another aspect, embodiments disclosed herein generally relate to a process for producing high purity and concentrated liquid products through electrocatalytic reaction in an electrosynthesis cell comprising a cathode compartment including a cathode electrode comprising a gas diffusion layer loaded with a selective electrocatalyst for reduction reactions; an anode compartment including an anode electrode comprising a gas diffusion layer loaded with a catalyst for oxidation reactions; a solid electrolyte compartment comprising a porous solid electrolyte, an inlet, and an outlet; a cation exchange membrane; and an anion exchange membrane. The process further includes supplying hydrogen gas or water solutions to the anode to be electrochemically oxidized on the oxidation reaction catalysts; and supplying an oxygen, CO2, CO, or N2 containing gas to the cathode to be selectively reduced by the selective reduction reaction catalyst; wherein the solid electrolyte compartment is separated from the cathode and the anode by the anion exchange membrane and the cation exchange membrane. The process further includes supplying deionized water or N2 gas to an inlet of the solid electrolyte compartment to flow through the porous solid electrolyte to bring out the generated liquid product.

In yet another aspect, embodiments disclosed herein generally relate to a porous solid electrolyte electrosynthesis cell for direct synthesis of high purity liquid products wherein the porous solid electrolyte electrosynthesis cell includes a cathode compartment including a cathode electrode including a gas diffusion layer loaded with a selective reduction reaction electrocatalyst for specific reduction reactions. The specific reduction reactions may include oxygen reduction reactions, CO2 reduction reactions, CO reduction reactions, N2 reduction reactions, nitrate reduction reactions and nitrite reduction reactions. The electrosynthesis cell may further include an anode compartment including an anode electrode comprising a gas diffusion layer loaded with a catalyst for oxidation reactions. The electrosynthesis cell may include a solid electrolyte compartment comprising a porous solid electrolyte, a first cation exchange membrane, and a second cation exchange membrane, where the solid electrolyte compartment may be separated from the each of the cathode and the anode by the first and second cation exchange membranes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1D show a (FIG. 1A) schematic of direct synthesis of H2O2 using diluted H2 and O2 under high pressure. FIG. 1B shows a schematic of direct electrosynthesis of H2O2 using pure H2 and O2 streams separated into anode and cathode, respectively. FIG. 1C shows an I-V curve of ORR on CB-10% catalyst using the standard three-electrode setup in a traditional flow-cell system with 1.0 M Na2SO4 (pH=7) and 1.0 M KOH as the electrolyte (pH=14) and FIG. 1D shows the corresponding FEs of H2O2 under different potentials.

FIG. 2 is a schematic design for an electrosynthesis cell for pure H2O2.

FIG. 3 is a schematic design for an electrosynthesis cell for CO2 reduction for the production of a variety of liquid products.

FIGS. 4A-4D show an (FIG. 4A) SEM image and (FIG. 4B) and BET surface area analysis of carbon black catalyst with different surface oxygen content. FIG. 4C shows a representative SEM image of a spray coated CB-10% electrode with a roughly 70 μm thick catalyst layer. FIG. 4D shows an enlarged SEM image of the CB-10% catalyst electrode demonstrating the high porosity of the catalyst layer on the GDL to provide for improved O2 diffusion and catalytic current density.

FIGS. 5A-5B show high-resolution (FIG. 5A) C 1 s and (FIG. 5B) O 1 s XPS spectra.

FIGS. 6A-6C shows (FIG. 6A) XPS survey scans of carbon black catalysts with different surface oxygen contents, (FIG. 6B) faradaic efficiencies, and (FIG. 6C) I-V curves of carbon black catalysts with different surface oxygen contents for 2e-ORR using O2//SE//H2O cell configuration with solid proton conductor.

FIGS. 7A-H show a comparison of the four types of TM-CNT samples, including Fe, Pd, Co, and Mn, which are demonstrated to have similar structures by transmission electron microscopy (TEM) (FIGS. 7A-D) and aberration-corrected high-angle annular dark-field scanning TEM (HAADF-STEM) (FIGS. 7E-H).

FIGS. 8A-8G show (FIG. 8A) SEM, (FIG. 8B) TEM and (FIG. 8C) high-resolution TEM views of the BOON nanosheet. FIG. 8D shows STEM-EDS elemental mapping of BOON. FIG. 8E shows TEM and (FIG. 8F) high-resolution TEM images of in-situ reduced metallic 2D-Bi. FIG. 8G shows in-situ Bi L3-edge XAS spectra of BOON at different potentials.

FIGS. 9A-9C show SEM images of solid polymer proton conductors. FIG. 9A shows a zoomed out SEM view of sulfonated styrene-divinylbenzene copolymer proton conductor with successive zoom in views FIG. 9B and FIG. 9C demonstrating a uniform spherical morphology.

FIG. 10 shows 2e-ORR performance of CB-10% in solid electrolyte for a three-electrode cell.

FIGS. 11A-11D show (FIG. 11A) The I-V curve of CB-10%//SE//Pt-C cell with H+ conducting porous solid-electrolyte. FIG. 11B shows the corresponding FEs and production rates of H2O2 under different cell voltages. FIG. 11C shows the dependences of H2O2 concentration on the DI water flow-rate under an overall current density of 200 mA/cm2. FIG. 11D shows the removal of TOC in Houston rainwater using the generated pure H2O2 solution under a current density of 200 mA/cm2.

FIGS. 12A-12B show stability tests of continuous generation of pure H2O2 solutions with concentrations over 1,000 and 10,000 ppm, respectively. No degradations were overserved in cell voltages and H2O2 concentrations over the 100-hour continuous operation. The cell currents and DI flow-rates are (FIG. 12A) 60 mA under and 27 mL h-1 and (FIG. 12B) 120 mA and 5.4 mL h-1, respectively.

FIGS. 13A-13B show H2O2 productivity of the presently described O2//SE//H2 system for (FIG. 13A) direct electrosynthesis and (FIG. 13B) direct synthesis compared with systems of the previous literature.

FIGS. 14A-14B show online H2 detection during H2O2 production and the XPS analysis of post-stability catalyst. FIG. 14A shows gas chromatography analysis of cathode gas flow of CB-10%//SE//Pt-C cell during H2O2production using O2 and H2. FIG. 14B shows XPS survey scans of CB-10% catalyst after stability test under a relatively high current density.

FIGS. 15A-15D show pure H2O2 generation using O2 and H2 with polymer anion conductor and inorganic proton conductor. The current densities over cell voltages of CB-10%//SE//Pt-C cell with (FIG. 15A) an inorganic CsxH3−xPW12O40 proton solid conductor and (FIG. 15B) anion conducting solid-electrolyte. The corresponding FEs and concentration of H2O2 products under different cell voltages are shown for (FIG. 15A) an inorganic CsxH3−xPW12O40 proton solid conductor and (FIG. 15D) anion conducting solid-electrolyte. Note that the DI flow-rate is 27 mL/h.

FIGS. 16A-16B show H2O2 faradaic efficiencies (FE)s as a function of DI water flow rate for (FIG. 16A) O2//SE//H2 and (FIG. 16B) scaled-up unit cell, showing that the H2O2 selectivity was inhibited with increased H2O2 concentration.

FIG. 17 shows a long-term operation test of the direct electro-synthesis of pure H2O2 solution using O2//SE//H2O cell, showing high selectivity and stability at 60 mA using this proposed system. The FE of H2O2 is maintained constant (˜95%) over the 100-hour continuous operation. The DI flow-rate is 27 mL/h.

FIGS. 18A-18B show (FIG. 18A) the I-V curve of an O2//SE//H2O cell where H2O is oxidized on the anode side into protons and O2. The 0.5 M H2SO4 in water solution was used for improving the ionic conductivity on the anode side, and was not consumed during electrosynthesis. FIG. 18B shows the corresponding FEs of H2//SE//H2O cell.

FIGS. 19A-19D show (FIG. 19A) the I-V curve and FEs of Air//SE//H2O cell for generating pure H2O2 solutions. It demonstrated the generation of pure H2O2 solutions at a high production rate of 2.3 mmol cm-2 h-1 (2490 mol kgcat-1 h-1) using only air and water as cathode and anode feedstock, respectively, when pure H2 and O2 are not available. FIG. 19B shows the I-V curve of the scaled-up unit cell module (80 cm2 electrode, no iR-compensation), and (FIG. 19C) the corresponding H2O2 FEs. It confirms that the present approach can be scaled up with negligible sacrifice in performance. FIG. 19D shows the dependence of H2O2 concentration (up to ˜20 wt. %) on the DI water flow-rate while maintaining an overall current of 8 A.

FIGS. 20A-20E show (FIG. 20A) the current densities over cell voltages on 2D-Bi catalyst using the electrosynthesis cell for CO2 reduction with H+ and HCOO— conducting solid-electrolyte. The corresponding faradaic efficiencies for the reduction products under different cell voltages using (FIG. 20B) H+ and (FIG. 20C) HCOO— conducting solid-electrolyte. FIG. 20D shows the dependencies of HCOOH concentration on the DI flow-rate maintaining an overall current density of 100 mA/cm2, indicating that concentrated pure HCOOH solution (up to 6.73 M) can be continuously produced. FIG. 20E shows the production of electrolyte-free C2+ liquid fuel solutions using commercial Cu2O catalyst, showing that small molecular oxygenates liquid fuels can also be efficiently collected.

FIG. 21 shows the long-term operation test of CO2 reduction to pure HCOOH solution demonstrating the high selectivity and the stability of the 2D-Bi catalyst at 30 mA/cm2 using this proposed CO2 reduction system. The FE of HCOOH maintains more than 80% over the 100-hour continuous operation.

FIGS. 22A-B displays the current-voltage profile (FIG. 22B) of the direct electrocatalytic CO2 hydrogenation cell (FIG. 22A) for HCOOH vapor generation.

FIGS. 23A-E show the ORR performance of M-CNT catalysts cast RRDE in 0.1M KOH. FIG. 23A shows linear sweep voltammetry measurements; FIG. 23B shows the calculated H2O2 selectivity and electron transfer number during potential sweep; FIG. 23C shows a stability measurement of Fe-CNT; and FIGS. 23D-E show a comparison of LSV and corresponding H2O2 selectivity.

FIGS. 24A-B show the effects of Fe atom loading at respective amounts of 0, 0.05, 0.1, and 0.2 at % on H2O2 activity and selectivity

FIGS. 25A-B show the bulk electrolysis for H2O2 generation in a homemade H-cell electrolyzer. FIG. 25A shows an SEM image of GDL supported catalyst at a loading of 0.5 mg cm-2, and FIG. 25B shows a polarization curve of Fe-CNT/GDL catalyst in 1 M KOH electrolyte

FIGS. 26A-B show the (FIG. 26A) XANES comparison of before, during, and after 2-h's continuous ORR electrolysis at 0.55 V vs. RHE and (FIG. 26B) EXAFS of post-catalysis Fe-CNT with Fe metal and Fe3O4 as references.

FIGS. 27A-D show the disinfection performance of Fe-CNT in neutral pH. FIG. 27A-B is an LSV of Fe-CNT catalyst on RRDE with corresponding selectivity under different potentials; FIG. 27C shows LSV of Fe-CNT catalyst on GDL electrode in an H-cell electrolyzer; FIG. 27D shows bulk electrolysis at a constant current density in PBS containing E. coli bacteria.

FIG. 28 shows the The disinfection efficiency as a function of treatment time.

FIGS. 29A-C show the production of pure HCOOH solution and vapor using optimized CO2 reduction system with solid electrolyte. FIG. 29A shows a Schematic illustration of the proposed four-chamber CO2 reduction cell with solid electrolyte. FIG. 29B shows the current densities over cell voltages and the corresponding HCOOH FEs. FIG. 29C shows the the concentration of pure KOH which is simultaneously produced using the four-chamber solid cell during CO2 reduction.

FIGS. 30A-C show ORR performance of the catalysts cast RRDE in: FIGS. 30A and 30C: 0.1 M KOH; FIGS. 30B and 30D: 0.1M Na2SO4. FIGS. 30A and 30B show linear sweep voltammetry (LSV) measurements of H2-annealed carbon black (denoted as ‘Pure C’) and boron, nitrogen, phosphorous, sulfur-doped carbon (denoted as ‘B-C’, ‘N-C’, ‘P-C’, ‘S-C’, respectively). FIGS. 30C and 30D show calculated H2O2 molar selectivity (left y-axis) and faradaic efficiency (right y-axis) during the potential sweep for different catalysts in 0.1M KOH and 0.1M Na2SO4, respectively.

FIGS. 31A-D show the three-electrode flow cell performance of catalysts. FIGS. 31A and 31B show I-V curves for Pure C, B-C and O-C in 1M KOH and 1M Na2SO4, respectively.

FIGS. 32A-B show solid-electrolyte cell performance for pure H2O2 generation. FIG. 32A shows I-V curve and corresponding H2O2 faradaic efficiency, and FIG. 32B shows H2O2 partial currents and H2O2 production rates under different applied potentials. FIG. 32C shows stability test of B-C fixed at 50 mA cm−2 of generation of ˜1,100 ppm pure H2O2 solution. The DI water feeding rate is fixed at 54 mL h−1.

FIG. 33 shows a schematic of a H2O2 production reactor with two cation exchange membranes on each of the cathode and anode side.

FIG. 34 shows the stability of Ni—N—C single atom catalyst in the all CEM solid reactor.

FIG. 35 shows the electrochemical 2e-ORR performance of B-doped carbon.

DETAILED DESCRIPTION OF THE INVENTION

Specific embodiments will now be described in detail with reference to the accompanying figures. Like elements in the various figures are denoted by like reference numerals for consistency.

In the following detailed description of embodiments, numerous specific details are set forth in order to provide a more thorough understanding.

However, it will be apparent to one of ordinary skill in the art that embodiments may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description.

In the following description, any component described with regard to a figure, in various embodiments of the present disclosure, may be equivalent to one or more like-named components described with regard to any other figure.

Throughout the application, ordinal numbers (e.g., first, second, third, etc.) may be used as an adjective for an element (i.e., any noun in the application). The use of ordinal numbers is not to imply or create any particular ordering of the elements nor to limit any element to being only a single element unless expressly disclosed, such as by the use of the terms “before,” “after,” “single,” and other such terminology. Rather, the use of ordinal numbers is to distinguish between the elements. By way of an example, a first element is distinct from a second element, and the first element may encompass more than one element and succeed (or precede) the second element in an ordering of elements, if an ordering exists.

One or more embodiments of the present disclosure relate to methods and systems for the production of high purity concentrated liquid products through electrocatalytic reactions.

One or more embodiments of the present disclosure relate to the production of H2O2. In yet another embodiment, the described electrosynthesis cell may be used in the production of highly pure formic acid and/or other liquid fuels through the elctrocatalytic reduction of CO2 or CO with solid electrolytes. Beyond the continuous production of pure H2O2, other pure liquid products including methanol, ethanol, n-propanol, formic acid, acetic acid and other organic oxygenates from CO2 reduction reactions (CO2RR) or CO reductions (CORR) can be realized utilizing the general process and electrosynthesis cell described in one or more embodiments of the present disclosure.

In accordance with one or more embodiments of the present disclosure, the produced liquid product may be produced through superior selectivity of employed catalyst to achieve the continuous production of high purity concentrated liquid products that do not require any additional separation steps to achieve pure product solutions.

One or more embodiments of the present disclosure may be directed towards processes for the highly efficient and large-scale synthesis of commercial-level concentrated H2O2 via a cost-effective electrocatalytic oxygen reduction route (ORR).

One or more embodiments of the present disclosure may relate to systems that may include a three-compartment electrosynthesis cell for direct pure liquid product production without any additional energy-intensive purification steps.

One or more embodiments of the present disclosure may relate to systems and methods that may include a four-compartment electrosynthesis cell for the simultaneously production of up to three kinds of high-purity products, in which an alkaline/neutral solution can be used for OER anode catalyst for direct pure liquid product production without any additional energy-intensive purification steps. In one or more embodiments, systems and methods that may include a four-compartment electrosynthesis cell, where the solid electrolyte may be split and separated by bipolar membrane. To separate the anode and cathode reaction. In such embodiments, noble metal catalysts of the anode may be excluded and/or replaced. For example, in one or more embodiments, a nickel iron layered double hydroxide (NiFe-LDH) and KOH may be chosen as the OER catalyst and electrolyte to decrease the catalyst cost and anode over potential.

One or more embodiments of the present disclosure are provided to introduce a highly efficient process and electrolytic cell capable of achieving high current efficiency for the direct and continuous production of pure (˜20wt %) hydrogen peroxide (H2O2) via electrocatalytic synthesis.

One or more embodiments of the present disclosure is directed to processes (electrosynthesis cell with highly active electrocatalyst) to achieve highly pure and concentrated liquid products from electrocatalytic reactions, e.g. 20 wt % pure H2O2 solution from ORR. Notably, unlike many traditional pure liquid product synthetic systems and processes, such as an H2O2 synthetic system, the present disclosure subverts the need for an energy-intensive purification step, as the immediate product of the governing system is an already pure form of H2O2 solutions.

One or more embodiments of the present disclosure may include a three-compartment electrolytic cell including a (cathode), a catalyst, such as IrO2/C for water oxidation or Pt/C for H2 oxidation (anode) and a solid electrolyte. More particularly, one or more embodiments herein relate to a process for the on-site production of highly pure hydrogen peroxide via electrocatalytic oxygen reduction reaction (ORR, O2+H2O+2e→HO2+OH), which can be used for bleaching, medical uses, food cleaning and processing, and other applications, together with oxygen at the counter side by water oxidation (OER, 2H2O→O2+4H++4e). In accordance with one or more embodiments, a three-compartment porous solid electrolyte electrolytic cell with solid electrolyte provided between a cathode and an anode is disclosed for carrying out this process.

In one or more embodiments of the present disclosure, the cathode and anode of the proposed cell may be catalyst coated gas diffusion layer (GDL) electrodes, which are separated by an anion and cation exchange membrane, respectively. Electrocatalytic reduction of oxygen (ORR) at the cathode and water oxidation at the anode may be used to generate anions (such as HO2) and cations (such as H+) respectively, which when driven through the appropriate ion exchange membranes ionically recombine to form pure H2O2. O2 generated at the anode can be driven back to the cathode to further undergo reduction, thereby contributing to the overall efficiency of the presented H2O2 synthetic system.

In accordance with one or embodiments described, the processes for the electrosynthesis of highly pure and concentrated liquid products may utilize a three-compartment electrolsynthesis cell, i.e. a cell partitioned into an anode compartment, an intermediate solid electrolyte compartment, and a cathode compartment wherein the cells are partitioned by cation or anion ion-exchange membranes, to produce liquid products.

As schematically illustrated in FIG. 1B, the cathode and anode of the proposed cell may be catalyst coated GDL electrodes, which were separated by anion and cation exchange membranes, respectively.

In one or more emboidments, porous solid ion conductors, e.g. H+ or HO2 conductors, may be filled in between the membranes or electrodes with close contact. In accordance with one or more embodiments, a PSMIM anion exchange membrane and a Nafion membrane may be used for anion and cation exchange, respectively. Other anion and cation exchange membranes may be used, alternatively. Two Nafion membranes may be used, alternatively. The solid electrolyte, as denoted in FIG. 1B, may be made of ion-conducting polymers with different functional groups, such as porous styrene-divinylbenzene copolymer consisting of sulfonic acid functional groups for cation conduction, or quaternary amino functional groups for anion conduction. Other forms of solid electrolyte used in batteries, such as ceramics, polymer/ceramic hybrids, or solidified gel electrolytes (e.g. 10 wt % H3PO4/polyvinylpyrrolidone gel), may also be employed. The cathode electrode where O2 is reduced can be supplied with humidified O2 gas to facilitate O2 mass transport, whereas the anode side can be circulated with an acid solution, such as 0.5 M H2SO4, for water oxidation using commercially-available IrO2/C catalyst. The anode side can also oxidize H2 to generate H+, in one or more embodiments.

In the electrosynthesis cell of one or more embodiments of the present disclosure, oxygen gas (or an oxygen-containing gas such as air) may be supplied to the cathode, while hydrogen gas or water is supplied to the anode. These gases may be externally fed. Alternatively, the two gases produced by water electrolysis can be rerouted and directly fed to the electrolytic cell.

Cathode

As schematically illustrated in FIG. 1B, the cathode of the electrosynthesis cell may be catalyst coated gas diffusion layer (GDL) electrodes. The cathode electrode may be included in the cathode compartment of the three-compartment electrosynthesis cell. The cathode electrode may include a gas diffusion layer that may be loaded with a selective reduction reaction electrocatalyst for specific reduction reactions. The specific reduction reactions may include one or more of, oxygen reduction reactions, CO2 reduction reactions, CO reduction reactions, N2 reduction reactions, nitrate reduction reactions and nitrite reduction reactions, or combinations thereof.

In one or more embodiments, the cathode may be selected from an oxygen-reducing electrode that includes a gas diffusion layer coated in a product selective electrocatalyst such as oxidized carbon material including carbon black, graphene, carbon nanotubes, or a mixture thereof. In one or more embodiments, the product selective electrocatalyst such as carbon material including carbon black, graphene, carbon nanotubes, or a mixture thereof, where the carbon material may include a non-metal dopant anchored on the carbon substrate. Non-metal dopants may include boron, nitrogen, phosphorous, sulfur, or a combination thereof. In another embodiment, examples of other electrocatalyst for coating a gas diffusion layer may includ N-, P-, S-, B-, Si-, or metal-doped carbon materials, or Bi, Cu, Ni, Fe, Co, Pd, In, Pb, Tn, transition metals, single atom catalysts of transition metals anchored into carbon nanotubes (CNT), oxides, chalcogenides thereof, or a mixture thereof.

In one or more embodiments, the cathode maybe comprised of a gas diffusion layer coated in a carbon black electrocatalyst that may be optionally oxidized. For example, in one or more embodiments, the carbon black may be pretreated before coating the GDL during the preparation of the cathode electrode. Carbon black may be acid treated to realize and optimize surface ether and carboxyl functionalization to improve selectivity towards the desired 2e-ORR pathway.

In one or more embodiments, the cathode of the electrosynthesis cell may be catalyst coated gas diffusion layer (GDL) electrodes where the catalyst may be loaded on the GDL electrode in an amount ranging from 0.01 mg/cm2 to 20 mg/cm2. In one or more embodiments, the cathode of the electrosynthesis cell may be catalyst coated gas diffusion layer (GDL) electrodes where the catalyst may be loaded on the GDL electrode in an amount ranging from 0.01, 0.1, 0.3, 0.5, 1, 3, 5, 7, and 9 mg/cm2 to 0.2, 0.3, 0.4, 0.6, 1, 2, 5, 8, 10, 15, and 20 mg/cm2, where any lower limit may be combined with any mathematically feasible upper limit.

In one or more embodiments, the specific electrocatalyst for H2O2 production may be a low-cost oxidized carbon black, which may be directly synthesized and treated by oxidation of commercial carbon black (such as Vulcan XR-72R) in acid solution. In one or more embodiments, carbon black may be oxidized by mixing and refluxing the carbon black in a concentrated acid solution for an amount of time ranging from 0.5, 1, 2, 3, 4, 6, 8, 10, 12, 16, 20, 24, 30, 36 and 40 hours (hrs) to 2, 3, 5, 8, 10, 12, 16, 20, 24, 30, 36, 40, and 48 hrs, where any lower limit may be combined with any mathematically feasible upper limit. For example, in one or more embodiments commercial carbon black may be oxidized in a solution of 12 M HNO3 for 3 hrs.

In one or more embodiments the treated and oxidized carbon black cathode catalyst may have a surface oxygen content ranging from 0.1, 1, 2, 3, 5, 7, 10, 15, 20, and 25% to 2, 3, 7, 8, 11, 13, 15, 18, 20, 25, and 30%, wherein any lower limit may be combined with any mathematically feasible upper limit.

In one or more embodiments, the cathode may be selected from an oxygen-reducing electrode comprised of a gas diffusion layer coated in a product selective electrocatalyst such as transition metal (TM) single atoms including Fe, Co, Ni, Cu, Zn, Pt, Pd, Ir, Mn, Cr that may be optionally anchored into carbon nanotube (TM-CNT) vacancies. For Example, the cathode may be selected from an oxygen-reducing electrode comprised of a gas diffusion layer coated in a product selective electrocatalyst such as Fe-CNT, Pd-CNT, Co-CNT, and Mn-CNT, or combinations thereof.

In one or more embodiments, the cathode may be selected from an oxygen-reducing electrode comprised of a gas diffusion layer coated in a product selective electrocatalyst such as transition metal (TM) single atoms and non-metal dopants that include B, N, O, F, S, P, Si, Cl, etc. For example, Fe—C—O single atom catalyst is shown herein to demonstrate an excellent H2O2 Faradaic efficiency in both alkaline and neutral pH (FIG. 4), which can be directly used in our solid electrolyte cell for pure H2O2 solutions.

In one or more embodiments, the single atom TM may anchored into the CNT in an amount ranging from 0.01 to 5 at %. In one or more embodiments the TM may anchored into the CNT in an amount ranging from 0.01, 0.05, 0.1, 0.15, 0.2, 0.3, 0.5, 0.8, 1, 1.5, 2, 3, and 4 at % to 0.1, 0.15. 0.18, 0.2 0.25, 0.3, 0.5, 0.8, 1, 1.5, 2, 3, 4, and 5 at %, wherein any lower limit may be combined with any mathematically feasible upper limit. For example, TM single atoms catalysts of one or more embodiments of the present disclosure may be prepared from metal cations (˜0.1 at %) that may be first dispersed onto commercial surface-functionalized CNTs as the carbon matrix, and suspended in water. They may then be further treated through steps of freeze drying and thermos annealing under inert gas at about 500 to 1000° C.

In one or more embodiments the product selective catalyst may be an ultrathin two-dimensional Bismuth (2D-Bi) catalyst for CO2-to-HCOOH conversion. In one or more embodiments the product selective catalyst may be an ultrathin two-dimensional Bi (2D-Bi) catalyst where at least 50% of the Bi sites of the 2D-Bi were electrochemically active using cyclic voltammetry. This high percentage may ensure high Bi atom efficiency during CO2RR catalysis.

In one or more embodiments, the electrosynthesis cell including a cathode of a gas diffusion layer coated in a product selective electrocatalyst may generate a liquid product with a Faradaic selectivity ranging from 10% to 99.9%. In one or more embodiments, the gas diffusion layer coated in a product selective electrocatalyst may generate a liquid product with a Faradaic selectivity ranging from 10, 20, 30, 40, 50, 60, 70, 80, 90 95, and 97% to 50, 60, 70, 80, 85, 90, 93, 95, 97, and 99.9%, wherein any lower limit may be combined with any mathematically feasible upper limit.

In one or more embodiments the electrosynthesis cell including a cathode of a gas diffusion layer coated in a product selective electrocatalyst may deliver a final liquid product with a tunable FE that ranges from 10% to 99.9%. In one or more embodiments the electrosynthesis cell including a cathode of a gas diffusion layer coated in a product selective electrocatalyst may deliver a liquid product with a FE that ranges from 30, 40, 50, 60, 70, 80, 90 95, and 97% to 50, 60, 70, 80, 85, 90, 93, 95, 97, and 99%, wherein any lower limit may be combined with any mathematically feasible upper limit. In one or more embodiments, the FE may be tunes by controlling the current density.

In one or more embodiments, the cathode electrode may have an electrode area that ranges from 1 cm2 to 10 m2 per unit cell, which can be scaled up by stacking multiple cells.

Anode

In one or more embodiments, the anode for use in the present disclosure may be selected from a gas diffusion electrode, hydrogen-oxidizing electrode, or a catalyst coated gas diffusion electrode, according to the electrolysis conditions. In one or more embodiments, examples of anode electrocatalyst for coating a gas diffusion layer include metal-doped carbon materials, or Ru, Jr, Pt, Ni, Ce, among other transition metals, single atom catalysts, an oxide or a chalcogenide thereof.

For example, the oxygen-generating electrode may be a gas diffusion layer coated with a catalyst electrode material consisting mainly of a metal such as platinum, iridium, or ruthenium, an oxide of such a metal, or an oxide metal carbon compound as a catalyst and is used as such. In other embodiments, the oxygen-generating electrode may be a gas diffusion layer coated with a catalyst electrode material consisting of a nickel iron layered double hydroxide (NiFe-LDH).

In one or more embodiments, the anode of the electrosynthesis cell may be catalyst coated gas diffusion layer (GDL) electrodes where the catalyst may be loaded on the GDL electrode in an amount ranging from 0.01 mg/cm2 to 10 mg/cm2. In one or more embodiments, the cathode of the electrosynthesis cell may be catalyst coated gas diffusion layer (GDL) electrodes where the catalyst may be loaded on the GDL electrode in an amount ranging from 0.1, 0.2, 0.3, 0.35, 0.4, 0.5, 0.8, 1, 1.5, 3, 5, and 7 mg/cm2 to 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, 1, 1.5, 3, 5, 8, and 10 mg/cm2, where any lower limit may be combined with any mathematically feasible upper limit.

In one or more embodiments, the anode electrode may have an electrode area that ranges from 1 cm2 to 10 m2per unit cell, which can be scaled up by stacking multiple cells.

Ion Exchange Membranes

In one or more embodiments, the ion exchange membrane may be a cation and/or anion exchange membrane. The cation and/or anion exchange membranes of the present disclosure may not be particularly limited. In one or more embodiments, the cation exchange membrane may be a perfluorosulfonic acid (PFSA) membrane and the anion exchange membrane may be a membrane comprising a co-polymer of polystyrene cross linked with divinylbenzene and polystyrene methyl imidazolium chloride (PSMIM). Other AEMs are also feasible, such as polybenzimidazole membrane (PBI), benzyltrimethylammonium grafted PTFE membrane, vinyl-benzyl chloride grafted fully fluorinated poly(tetrafluoroethylene-co-hexafluoropropylene) membrane and chloromethylated polysulfones membrane.

In one or more embodiments, the cation and anion exchange membranes may be interchangeable or selectively used in multiple configurations at either the cathode side or the anode side of the electrosynthesis cell.

Solid Electrolyte

In one or more embodiments, the solid electrolyte material disposed between the cathode and anode may include ion-exchange resins and matrixes comprising an ion-conducting material.

In one or more embodiments, the porous solid electrolyte may be selected from a group of ion conducting polymers including polymers or copolymers of styrene, acrylic acid, aromatic polymers, or a combination thereof.

In one or more embodiments, the porous solid electrolyte may be selected from an inorganic ceramic solid electrolyte, a polymer/ceramic hybrid solid electrolyte, solidified gel electrolytes, or ion conducting polymers, or a combination thereof.

In one or more embodiments, the porous solid electrolyte is a porous styrene divinylbenzene copolymer consisting of sulfonic acid functional groups for cation conduction, or quaternary amino functional groups for anion conduction.

In one or more embodiments, the solid electrolyte resins may include hydrocarbon resins such as styrene polymers, acrylic acid polymers and aromatic polymers. The sulfonated inorganic materials, like sulfonated carbon, SiO2, TiO2, WO3, CeO2, TiC, MoC et al., may also be used as solid electrolyte. The solid proton conductor may be prepared by refluxing porous (pore size ranges from 2 nm to 100 nm) or solid polymer or inorganic matrix in fuming acid, such as H2SO4 for about 24-h at an elevated temperature of about 80° C.

In one or more embodiments of the present disclosure, the solid electrolyte comprised ion-conducting polymers with different functional groups, such as porous styrene-divinylbenzene copolymer consisting of sulfonic acid functional groups for H+ conduction, or quaternary amino functional groups for anion conduction. The solid electrolyte is not limited and may be an anion polymer conductor for anion or an inorganic solid cation conductor for pure generation comprised of CsxH3-xPW12O40. The porous styrene-divinylbenzene copolymer may be one of styrene-divinylbenzene sulfonated copolymer such as SSE 50 or SSE 300. One or more embodiments may comprise other forms of solid electrolytes, such as ceramics, polymer/ceramic hybrids, or solidified gel electrolytes (e.g. 10 wt % H3PO4/polyvinylpyrrolidone gel).

Gas Diffusion Layer Electrode

In one or more embodiments, the gas diffusion layers of the present disclosure are not particularly limited. In one or more embodiments, the gas diffusion layer may be a thin carbon-based porous medium that must provide high electrical and thermal conductivity and chemical and corrosion resistance, in addition to controlling the proper flow of reactant gases (hydrogen and air) to ensure uniform distribution of reactive gases on the surface of the electrodes. In one or more embodiments, the gas diffusion layers may be coated in a catalyst to form either the cathode or anode of the electrosynthesis cell.

Gas Feed

In one or more embodiments, the hydrogen gas and oxygen gas may be supplied, or hydrogen and oxygen gases may be generated by water electrolysis and may be directly supplied to the electrolytic cell.

In one or more embodiments the cathode side may be supplied with a controlled and tunable amount of O2, CO2, CO, N2, air, or other reactants and the anode side may be supplied with enough of H2, H2O, alkaline solutions, acidic solutions, or other reactants.

In one or more embodiments the cathode side may be supplied with a controlled and tunable amount of gas at a flow rate ranging from 0.001 to 1000 SLM. In one or more embodiments, the gas flow rate may change depending upon the device capacity.

Pure Water Feed

In one or more embodiments, pure water may be fed to the solid electrolyte compartment at a suitable rate depending on the size of reactor and the need of product concentration. In one or more embodiments, the water flow rate in a unit cell (one cathode and one anode) may range from 1 uL/h to 10 m3/h. In one or more embodiments, the specific water flow rate may be tuned relative to the target product fluid and its concentration.

Liquid Products Formed

The process and electrosynthesis cell according to one or more embodiments may be used to obtain pure liquid products such as H2O2, methanol, ethanol, n-propanol, formic acid, acetic acid, other organic alcohols and acids, or ammonia from CO2 reduction reactions (CO2RR), CO reduction reactions, N2 reduction reactions, nitrate or nitrite reductions, and so on.

In one or more embodiments, the electrosynthesis cell may capable of generating a concentrated liquid product. For example, in one or more embodiments the electrosynthesis cell may generate a liquid product, such as H2O2, with a concentration ranging from 0.01 to 20 wt. %. in one or more embodiments the electrosynthesis cell may generate a liquid product, such as H2O2, with a concentration ranging from 0.01, 0.1, 1, 3, 5, 8, 10, 14, 16, and 18 wt. % to 8, 10, 12, 14, 16, 18 and 20 wt. %, wherein any lower limit may be combined with any mathematically feasible upper limit.

In one or more embodiments, the electrosynthesis cell may be tuned to selectively operate at a current density ranging from 1 mA/cm2 to 100 A/cm2.

In one or more embodiments, the electrolysis conditions of the electrosynthesis cell may include operating at a liquid temperature ranging from 1 to 95° C.

Electrosynthesis Cell

In one or embodiments wherein a pure product, such as hydrogen peroxide (H2O2), may be obtained, O2 may be reduced by the H2O2-selective catalyst, and the generated negatively charged HO2 may then be driven by the electrical field to travel through the AEM towards the middle solid electrolyte channel. At the same time, protons generated by water oxidation or hydrogen oxidation on the anode side may move across the CEM to compensate the charge. Depending on the type of ion-conducting polymers in between, pure H2O2 product can be formed via the ionic recombination of crossed ions either at the left (H+-conducting polymer) or right (HO2 conducting polymer) interface between the middle channel and membrane. Then, the formed liquid products may be quickly released by the slow deionized water (DI) stream or humidified inert gas flow.

Pure liquid product solutions with a wide range of concentrations may be produced by adjusting the flow rate of the DI and gas as demonstrated in the examples below. In one or more embodiments, the DI flow rate may be at least 1 ul/hr and may be dependent on the size and/or capacity of the device.

In one or more embodiments the cathode electrode, where O2 is reduced, may be supplied with humidified O2 gas to facilitate O2 mass transport, whereas the anode side may be circulated with a solution such as 0.5 M H2SO4 for water oxidation using commercial-available IrO2/C catalyst, or H2 gas using commercial-available Pt/C catalyst.

As illustrated in FIG. 1B, H2 and O2 streams are separated into anode and cathode, respectively, avoiding their mixture as in the case of direct synthesis (FIG. 1A).

On the anode side, H2 can be electrochemically oxidized on a HOR catalyst, which may be coated on a gas diffusion layer electrode, into H+; on the cathode side, by designing a 2e-ORR selective catalyst, O2 can be selectively reduced through the 2e− pathway into HO2 (Eq. 1), instead of OH as in traditional H2/O2 fuel cells. Both HOR and 2e-ORR catalysts are in close contact with cation and anion exchange membranes (CEM and AEM), respectively, to avoid flooding issues from the direct contact with liquid water.

As shown in FIG. 2, the electrochemically generated anions (HO2) and cations (H+) then move across the corresponding membranes into a thin layer of porous solid electrolyte, which plays a key role in both ion conduction and pure product collection. First, ions can be efficiently conducted through the solid electrolyte with small ohmic losses for high cell efficiencies, particularly under large current densities. Second, H2O2 molecules can be formed via the ionic recombination of crossed HO2 and H+ ions in the solid electrolyte layer, which were dissolved in the DI water stream and quickly released as pure H2O2 solutions with no other impurity ions involved. By tuning the HO2 generation rate or the DI water flow rate, a wide range of H2O2 concentrations (from hundreds of ppm to tens of percentage) can be directly obtained for different purposes of use. No further energy-consuming downstream purifications are needed in this case, dramatically differentiating the present electrosynthesis design and process from traditional anthraquinone process or direct synthesis methods.

The porous solid electrolyte may be either anion or cation solid conductor, which can be made of ion conducting polymers with different functional groups, inorganic compounds, or other types of solid electrolyte materials such as ceramics, polymer/ceramic hybrids or solidified gels.

With different solid electrolyte properties, the electrosynthesis cell and process can be further extended to other electrocatalytic synthesis of pure products beyond H2O2, such as CO2 reduction, N2 reduction and so on. For example, FIG. 3 illustrates an electrosynthesis cell for the reduction of CO2 wherein the anode is coated with a stable and active HOR or oxygen evolution reaction catalyst (OER, in acidic solutions), which helps release H+ from water to compensate for negative charges of generated formic acid ions.

The electrosynthesis cell and process in accordance with one or more embodiments of the present disclosure may be able to achieve high H2O2 selectivity of 95%, productivity (at 180 mA/cm2 partial current or 3660 mol/kg cat h), and a liquid product concentration of 20 wt. %.

Additionally, a 100-hour continuous and stable generation of ˜1.1 wt. % (˜11,000 ppm) pure H2O2 solution is demonstrated herein. It is also shown that similar H2O2 activity and selectivity can be obtained while using air and water for 2e-ORR and oxygen evolution reaction (OER), respectively, making on-site applications more accessible compared to pure H2 and O2. To demonstrate potential applications, the total organic carbon (TOC) in Houston rainwater was successfully treated with a processing rate up to 2180 L m-2electrode h-1 to meet Texas drinking water standards, as demonstrated below.

To deliver efficient energy conversions, electrocatalysts with high activity and selectivity for 2e-ORR and HOR/OER are a prerequisite. It is straightforward to employ the state-of-the-art platinum on carbon (Pt/C) catalyst for HOR at the anode side with high H2-to-H+ conversion rates and small over-potentials. On the other side, however, electrocatalysts with both high activity and selectivity for 2e-ORR towards H2O2 are much less explored compared to the extensively studied 4e-ORR to H2O in fuel cell catalysis.

Selective Electrocatalysts for H2O2

Commercial carbon black is demonstrated herein as the starting material due to the following detailed and demonstrated reasons. First, it is significantly cheaper than graphene and/or noble metals, which makes it particularly suitable for large-scale applications. Second, it has a high surface area (FIGS. 4A-4D) for high mass activities; and third, it is different from graphene nanosheets where their layer-by-layer stacking can block gas diffusions. The nanoparticulate morphology of carbon black allows for effective O2 diffusions from GDL to the surface layer of catalyst (FIGS. 4C-4D). This ensures efficient operations particularly under large current densities. For carbon materials, surface functional groups such as ether (C—O—C) and carboxyl (HO—C═O) have been identified to possibly activate the adjacent carbon atomic sites for selective 2e-ORR. Hence, carbon black nanoparticles may be treated in nitric acid to realize surface ether and carboxyl functionalization.

EXAMPLE 1 Preparation and Treatment of Carbon Black Catalysts

To demonstrate, three example compositions of carbon black were prepared by adding 600 mg of commercial carbon black (XC-72, FuelCellStore) into 600 mL of 12.0 M nitric acid. Then, the above solution was refluxed at 85° C. for 1, 3 and 12 h, respectively, to obtain oxidized carbon black with surface oxygen content of 7.33%, 10.19% and 11.62%, respectively. After natural cooling, the slurry was taken out, centrifuged and washed with water and ethanol until the pH was neutral. Finally, the sample was dried at 70° C. in a vacuum oven. The as-received commercial carbon black shows a 2.33% surface oxygen content. Otherwise, a comparative 500 mg sample of commercial carbon black was annealed in a tube furnace at a temperature of 500° C. for 2 h under a mixed hydrogen (5%)/argon atmosphere to obtain the surface oxygen-free carbon black. Following the preparation of the functionalized carbon black examples, appropriate characterization was conducted as detailed below.

No morphological evolution was observed for those carbon black nanoparticles after acid treatment (FIG. 4B). The high-resolution X-ray photoelectron spectroscopy (XPS) spectra of treated carbon black (FIGS. 5A-5B) confirmed that the acid treatment enriched oxygen-containing functional groups, including C—O—C/C—OH and HO—C═O as de-convolved from carbon and oxygen is regions. The carbon is spectrum, shown in FIG. 5A, of the CB-10% catalyst can be de-convoluted into five contributions that are sp2 carbon at 284.6 eV, sp3 carbon at 285.5 eV, C—O at 286.8 eV, —COOH at 288.9 eV and the characteristic shakeup line of carbon in aromatic compounds at 291.2 eV (π-π* transition). The O 1 s peaks, shown in FIG. 5B, could be de-convoluted into three peaks. The components centered at 531.7 and 532.9 eV were attributed to the C—OH/C—O—C and C═O surface functional groups, respectively. The last component with B.E. around 535.5 eV was characteristic of adsorbed water. These results indicate that the acid treatment induced surface oxygen functionalization of carbon black.

Surface characterization was further conducted to tune the surface oxygen on carbon black for optimized ORR performance. Carbon black with different surface oxygen contents and IrO2—C was used as cathode and anode catalyst, respectively. The cathode side was supplied with 50 sccm of humidified O2 gas. The anode was circulated with 0.5 M H2SO4 for water oxidation. The surface oxygen strongly correlates to the H2O2 selectivity and activity (FIG. 6A). The maximal H2O2 selectivity of carbon black quickly ramped up to ˜98% with relatively low surface oxygen coverage (2.11%), whereas that of oxygen-free carbon black was only ˜80% (FIG. 6B). While the H2O2 selectivity was not obviously enhanced by further increasing the surface oxygen from 2.11 to 11.62%, it was found that the ORR catalytic activity was gradually improved (FIG. 6C). This improvement can be ascribed to the increased concentration of active sites for 2e-ORR. After optimization, carbon black with ca. 10% surface oxygen coverage (CB-10%) was selected as the cathode catalyst for efficient 2e-ORR.

A standard three-electrode setup was used to evaluate the intrinsic activity of CB-10%. H2O2 can be reliably detected at 0.56 and 0.82 V vs. reversible hydrogen electrode (RHE) in 1.0 M Na2SO4 and 1.0 M KOH electrolyte, respectively (FIG. 1C). With a wide potential window to deliver high H2O2 selectivity (>90%) in both neutral and alkaline solutions, the catalyst reached a maximal faradaic efficiencies (FEs) of 98 and 99%, respectively (FIG. 1D). More importantly, impressive H2O2 partial currents of 410 and 300 mA/cm2 were achieve while high FEs were still maintained in alkaline and neutral solutions, respectively, which is among the highest O2-to-H2O2 conversion rates achieved so far.

EXAMPLE 2 Preparation and Analysis of Single Atom TM-CNT

In one or more embodiments, as indicated, the cathode may be selected from an oxygen-reducing electrode comprised of a gas diffusion layer coated in a product selective electrocatalyst such as transition metal (TM) single atoms including Fe, Pd, Co, and Mn that may be optionally anchored into carbon nanotube (TM-CNT) vacancies.

In the following example TM-CNT catalysts were prepared by an impregnation and reduction method. In the synthesis of Fe-CNT, a 7.5-mM iron nitrate stock solution was first prepared by dissolving Fe(NO3)3.9H2O (ACS Grade, Alfa Aesar) into Millipore water (18.2 MΩ·cm). A carbon suspension was prepared by mixing 50 mg multi-walled carbon nanotubes (Carbon Nanotubes Plus GCM389, used as received) with 20 mL of Millipore water, and tip sonicated (Branson Digital Sonifier) for 30 min till a homogeneous dispersion. Then 200 μL of Fe2+ solution, given a raw atomic ratio of Fe:C to be ˜0.1 at. %, was dropwise added into CNT solution under vigorous stirring, followed by a quickly frozen in liquid nitrogen. The as-prepared Fe(NO3)3/CNT powder was heated up in a tube furnace to 600° C. at a pressure of 1 Tor and a gas flow of 100 sccm Ar (UHP, Airgas) within 20 min, and kept at same temperature for another 40 min before cooling down to room temperature.

Other Pd-, Co-, and Mn-CNTs were prepared in a similar way to Fe-CNT except for various metal salt precursors, i.e., Pd(NO3)2.2H2O, Co(NO3)2.6H2O, and Mn(NO3)2.4H2O (Puriss or ACS Grade, Sigma-Aldrich), respectively.

N doped Fe-N-CNT was prepared by heating up the above-mentioned Fe(NO3)3/CNT powder under a same temperature program with Fe-CNT but within a mixed gas flow of 50 sccm NH3 (anhydrous, Airgas)+100 sccm Ar.

FIGS. 7A-H show a comparison of the four types of TM-CNT samples, including Fe, Pd, Co, and Mn, which are demonstrated to have similar structures by transmission electron microscopy (TEM) and aberration-corrected high-angle annular dark-field scanning TEM (HAADF-STEM). No nanoparticles or clusters were observed in the bright field TEM images by different scales as shown by FIGS. 7A-D. This suggests a good dispersion of TM atoms. Isolated TM atoms can be resolved by HAADF-STEM due to their high Z-contrast compared to those neighboring light elements such as C or O. While all four isolated metal atoms were observed as the white dots in FIG. 7E-H, Pd-CNT presents the most distinguishable single atoms due to its heaviest atomic mass compared to the other three metal elements. In addition, the oxidation state of coordinated Fe is lower than simply adsorbed Fe on CNT, suggesting the different chemical environment between the adsorption case and coordination case

Among the different potential transition metals carbon nanotube catalysts, Fe-CNT is further demonstrated herein to provide excellent performance towards H2O2 generation in terms of activity and selectivity. Fe-CNT was analyzed as a representative of other M-CNTs

An improved onset potential to reach 0.1 mA cm−2 H2O2 generation current is achieved at only 0.822 V versus reversible hydrogen electrode (vs. RHE) in 0.1 M KOH on rotating ring-disc electrode (RRDE), while a peak H2O2 selectivity of more than 95% is delivered in both alkaline and neutral pH. With the O2 mass transport facilitated by a gas diffusion layer (GDL) electrode, the H2O2 generation rate by Fe-CNT can reach to 43 mA cm−2 with a 95.4% selectivity under only 0.76 V. By switching the neighboring O with N coordination (through doping), the 2e ORR pathway can also be successfully shifted towards 4e of H2O, demonstrating a wide range of reaction tunability in this materials platform.

Density functional theory (DFT) calculations were conducted and suggest that the catalytically active C and Fe sites in Fe—C—O and Fe—C—N motifs may be responsible for the H2O2 and H2O pathways, respectively. In a variety of Fe—C—O motifs calculated, the incorporation of Fe atoms significantly improves their catalytic activities for H2O2 generation compared to those with only O dopants. As a prototype demonstration of potential applications, this high-performance H2O2 generation catalyst enables an effective water disinfection of >99.9999% bacteria removal at a treating rate of 125 L h−1m−2electrode

Selective Electrocatalyst for HCOOH in CO2 Reduction Reaction

Similarly, other electrocatalyst were explored, in particular towards specific selectivity to HCOOH from CO2 reduction. In one or more embodiments, when the target liquid product is HCOOH a variety of HCOOH-selective electrocatalysts, such as Bi, Co, Pd, In, Pb, Sn, and carbonaceous material, could be coupled into the electrosynthesis cell for a CO2RR system for pure HCOOH solution generation. Among them, Bi-based catalysts are demonstrated herein to have achieved peak faradaic efficiencies (FEs) of over 95% under high current densities (>50 mA/cm2), outperforming most of other non-noble metal catalysts. CO2 reduction to formate was the most energetically favorable among the competing cathodic processes on Bi surface. However, large overpotentials were usually required to drive significant CO2RR currents, which leads to low energy conversion efficiencies. More importantly, conventional Bi-based electrocatalysts generally involve multi-step or complicated synthesis methods, making it difficult for low-cost and largescale productions in the future.

A facile and scalable hydrolysis approach was developed, followed by in-situ electrochemical-reduction to synthesize ultrathin two-dimensional Bi (2D-Bi) catalyst for CO2-to-HCOOH conversion, which thereby presents abundant under-coordinated active Bi sites for significantly improved catalytic performance. Due to the simplicity of the synthesis method, kilogram-scale synthesis of this Bi catalyst has been demonstrated using a 1-liter reactor.

EXAMPLE 3 Synthesis of Two-Dimensional Bi (2D-Bi) Catalyst for CO2-to-HCOOH Conversion

Specifically, commercial bismuth nitrate was firstly hydrolyzed to form layered basic bismuth nitrates—Bi6O6(OH)3(NO3)3.1.5H2O (BOON) which was then topotactically converted into 2D-Bi by in-situ electro-reduction. During the hydrolysis step, cetyltrimethylammonium bromide (CTAB) was used as surface capping agent to obtain ultrathin 2D-Bi. Br− ions have been demonstrated to suppress the stacking of monolayers for Bi-compound during bottom-up synthesis system, and the extra surface repulsion from the hydrophobic long chains of CTA+ ions could further terminate the stacking of layered basic bismuth nitrates.

Scanning electron microscopy (SEM) and aberration-corrected transmission electron microscopy (TEM) images (FIGS. 8A-8B) showed the few-layer-thick BOON nanosheets with good homogeneity. Notably, the nanosheets were almost transparent to the electron beam, indicating their ultrathin feature. The lattice spacing in the high-resolution TEM image was measured to be 0.288 nm (FIG. 8C), corresponding to the (006) planes of tetragonal BOON. In addition, the corresponding fast Fourier transform (FFT) analysis of an individual BOON nanosheets indicated its single-crystalline nature. Scanning transmission electron microscopy-energy dispersive spectroscopy (STEM-EDS) elemental mapping (FIG. 8D) showed a uniform distribution of Bi, O, N, C and Br of the BOON nanosheet, confirming the CTAB capping effect. The BOON nanosheets were then electrochemically reduced to 2D-Bi metal in CO2-saturated 0.5 M KHCO3 solution. The XRD measurement of the reduced material showed obvious diffraction peaks assignable to metallic Bi, consistent with the X-ray photoelectron spectroscopy (XPS) analysis. The XPS and STEM-EDS studies also demonstrated the absence of Br at the Bi surface, suggesting the formation of clean metallic Bi. It is noted that the in-situ formed Bi metal retains the original nanosheet morphology of BOON (FIG. 8E). The lattice spacing in FIG. 8F is 0.238 nm, agrees well with the interplanar spacing in rhombohedral Bi. The thicknesses of individual Bi nanosheet determined by atomic force microscopy (AFM) was only a few nanometers, revealing its 2D nature with maximally exposed surface sites. It is also interesting that the present process results in 2D-Bi with quasi-single-crystal nature, which could benefit in-plane electron transportation. In addition, it was found that ca. 59.8% Bi sites of 2D-Bi were electrochemically active using cyclic voltammetry. This high percentage could ensure high Bi atom efficiency during CO2RR catalysis.

In-operando X-ray absorption spectroscopic (XAS) can help to elucidate the electronic structure change of the Bi catalyst under reaction conditions. FIG. 8G further shows the in-situ Bi L3-edge normalized absorption spectra under different applied potentials, as well as commercial Bi metal as a reference. A negative energy shift of Bi edge was observed from open circuit voltage (OCV) to −0.32 V vs. reversible hydrogen electrode (RHE), suggesting the reduction of Bi oxidation states. With the negative potential further increased to −0.92 V, the Bi L3-edge spectra overlapped with metallic Bi reference, which indicated that the active phase under CO2RR conditions was metallic.

Electrosynthesis Cell for H2O2 Production

EXAMPLE 4 Electrocatalytic Characterization of Carbon Black Catalyst

The excellent 2e-ORR and HOR performances of CB-10% and Pt-C catalysts therefore make good preparations for the direct electrosynthesis of pure H2O2 solutions using the presently described design with solid electrolytes. In one or more embodiments styrene-divinylbenzene copolymer microspheres (FIGS. 9A-9C), consisting of sulfonic acid functional groups for cation (H+) conductions, serves as the SE layer with micron pores in between for water flow and product release. Other types of solid electrolytes including anion (HO2) polymer conductors and cation inorganic conductors were also demonstrated for pure H2O2 generation. It was first confirmed that there are no obvious negative or positive impacts on H2O2 selectivity of CB-10% catalyst when switching from traditional liquid electrolyte to the solid electrolyte in a standard three-electrode setup (FIG. 10), which different from the two-electrode cell, can also calibrate the potentials in RHE scale. FIG. 10 plots the I-V curve of CB-10%//SE//Pt-C cell with O2 and H2 gas streams in the cathode and anode, respectively.

It is noted that, for all of the two-electrode cell measurements in this work, the cell voltages are defined as negative when the device can output electrical energy during the production of H2O2. The positive cell voltages thereby suggest the external energy input to this reactor. The DI water flow rate was fixed at 27 mL/h for this 4 cm2 electrode cell to prevent significant product accumulation particularly under large currents. H2O2 was readily detected starting from a cell voltage of −0.54 V, suggesting an early onset considering the equilibrium voltage of −0.76 V (30). The H2O2 selectivity was maintained above 90% across the whole cell voltages, reaching upto a maximum of 95% (FIG. 11B).

An H2O2 generation current of ˜30 mA/cm2 (0.53 mmol/cm2 h) can be obtained under 0 V (no external energy input), indicating an energy-efficient route compared to traditional anthraquinone or direct synthesis methods. In addition, only 0.61 V cell voltage was required to deliver a significant current density of 200 mA/cm2 with a high H2O2 FE of ˜90%. This large current represents an H2O2 generation rate of 3.37 mmol/cm2 h, or 3660 mol kgcat-1 h-1 considering both cathode and anode catalyst, setting up a new productivity benchmark in both direct synthesis and electrosynthesis of H2O2 (Table 1 and FIGS. 13A-13B). No H2 byproduct (possibly from H2 evolution due to large overpotentials) was detected from the cathode side under such a high current density (FIG. 14A), indicating an exclusive ORR. Other types of solid electrolyte with different material properties, including anion polymer conductors for anion conduction and cation inorganic compound conductors (CsxH3-xPW12O40), can also be employed for pure H2O2 solution generation (FIGS. 15A-15D), which suggests the wide tunability and versatility of the solid electrolyte design. The relatively low H2O2 FEs for cell using anion conducting solid-electrolyte is probably caused by the self-decomposition of H2O2 in the solid electrolyte layer as significant gas bubbles observed, as the anion conducting solid-electrolyte provides a high alkaline environmental for ion-conduction.

Under the fixed DI water flow rate of 27 mL/h, the produced H2O2 concentration from the electrosynthesis cell can reach up to ˜1.7 wt. % with an overall cell current of 800 mA (4 cm2 electrode). By speeding up or slowing down the DI water flow rate while maintaining the H2O2 generation current, a wide range of product concentrations may were obtained which could satisfy different application scenarios (FIG. 11C). Up to 20 wt. % (200,000 ppm) concentrated pure H2O2 solutions can be directly and continuously obtained via electrochemical synthesis.

It was observed that the H2O2 selectivity was inhibited with increased H2O2 concentration (FIG. 16A). This observed decrease (98% at 0.3 wt. % vs. 70% at 6.6 wt. %) was ascribed to the following three reasons: the concentrated H2O2 solution in the solid electrolyte layer 1) may self-decompose into O2 and H2O during the present quantification process; 2) may thermodynamically retard the 2e-ORR while the selectivity of the competing 4e− pathway picks up; and 3) may diffuse across the CEM and become oxidized on the anode side as frequently observed in methanol or formic acid fuel cells.

In addition to the activity and selectivity, long-term stability is another important metric for evaluating catalysis. The electrosynthesis device demonstrated a 100-hour continuous and stable production of ˜1,200 ppm and ˜11,000 pure H2O2 solutions with no degradations in H2O2 activity and selectivity (FIGS. 12A and 12B). XPS characterization of post-catalysis CB-10% catalyst reveals that its surface oxygen was robust and cannot be electrochemically reduced during the operation of ORR (FIG. 14B).

TABLE 1 Performance metrics of different H2O2 generation methods. Max. Productivity Productivity Selectivity Concentration Purity (mol kgcm−1 h−1) (mmol cm−1 h−1) (%) Stability (ppm) Our Method Pure 3660 3.4 90~95 >100 h 200,000 Direct Mixture 60.8~180 N/A 80.7~96   Up to 4 cycles 5,300 Synthesis (8, 9, 34-36) or 4 h Electro- Mixture N/A 0.05~1.2   47~93.5 2~6 h 3,400~60,000 chemical (37-42) Synthesis Pure N/A 0.289 26.5 6 h 80,000 (19)

Possible impurities in collected products, examined by inductively coupled plasma atomic emission spectroscopy (ICP-OES), such as sodium (common impurity ions in water), iron (from device), sulfur (from SE), and platinum (from anode), were at ppm or lower level, demonstrating the ultra-high purity of the generated H2O2 solutions. Table 2 shows the concentration of impurities for generated H2O2 using O2//SE//H2O cell. Note that the reported concentrations are average results acquired from 5 independent tests. Therefore, those electrochemically synthesized pure H2O2 are ready for immediate use out of the cell without any further purification processes, reducing a significant portion of cost compared to other methods, and more importantly simplifying the setup for the deployment of delocalized generation in the future.

Table 2. Shows the concentration of impurities for generated H2O2 using O2//SE//H2O cell.

Sodium Iron Sulfur Platinum 0.872 ppm 0.022 ppm 2.62 ppm Lower than detection limit

Application of Product for Water Purification

EXAMPLE 5 Water Purification

This renewable and simple on-site generation of pure H2O2 solutions opens great opportunities in practical applications ranging from drinking water treatment, disinfection, bleaching and so on. Rainwater is one of the most important drinking water supply for much of the world's population, which however may contain contaminates such as bacteria, or small organic molecules particularly in industrial area, such as Houston. Compared to the traditionally used chlorine compounds which may produce carcinogens in the processed drinking water, H2O2 is safe to both human health and environments when disinfecting bacteria and decomposing organics. Specifically, it is capable of removing total organic carbon (TOC) contaminants in rainwater for drinking.

The generated H2O2 stream (200 mA/cm2, 4 cm2 electrode, 27 mL/h DI water flow) was directly mixed with the rainwater stream with a tunable feeding rate to optimize the purification efficiency. The TOC of the pristine rainwater collected in Houston was detected to be ˜5 ppm, which is above the Texas treated water standard of ˜2 ppm. As shown in FIG. 11D, the TOC was gradually decreased when the rainwater feeding rate was slowed down, demonstrating the efficacy of H2O2 in water treatment. A maximal processing rate of 2180 L/(m2 electrode hr) was achieved in bringing down the TOC level to meet the drinking water standards, making the design appealing for practical rainwater treatment when scaled-up.

EXAMPLE 6 Anode Water Oxidation Coupling with ORR

It was also demonstrated that the oxidation reaction on the anode side, to be coupled with the cathode 2e-ORR, could be flexibly changed for applications where H2 is not available. Water oxidation to O2 with protons released can be more easily accessed than HOR. Sulfuric acid (0.5 M H2SO4) was added in water to reduce the ionic resistance on the anode side, where H2SO4 was not consumed during catalysis and continuously circulated. FIG. 18A exhibits the I-V curve of O2//SE//H2O cell, with the corresponding H2O2 FEs and production rates shown in FIG. 18B. Further analysis provided that the H2O2 selectivity under the same current densities is very close to that of O2//SE//H2 design (FIG. 11B), ruling out any impacts on the cathode 2e-ORR catalysis when the anode reaction was changed. Similarly, high H2O2 productivity of 3.3 mmol cm-2 h-1 (3565 mol kgcat-1 h-1) can be achieved at a cell voltage of 2.08 V, representing an electricity-to-chemical energy conversion efficiency of 22.6% to deliver this practical production rate. The ultra-high purity of synthesized H2O2 was confirmed using ICP-OES with negligible amount of impurities. A 100-hour continuous generation of pure H2O2 solutions suggested the high stability of O2//SE//H2O cell (FIG. 17). To further simplify the design instead of using pure O2, air was directly pumped into the cathode side as the O2 source for 2e-ORR (FIG. 18A). While higher cell voltages were required to drive the reaction due to dramatically decreased O2 concentration/activity, the Air//SE//H2O cell still presented high H2O2 selectivity of over 90%. A maximal H2O2 partial current of ˜123 mA/cm2 was reached at 2.36 V, corresponding to an impressive H2O2 productivity of 2.3 mmol cm-2 h-1 (2490 mol kgcat-1 h-1).

Scalability and Stability

Example 7 Scalability

To validate the scalability of the porous solid electrolyte design for large-scale synthesis of pure H2O2 solutions, the electrode area was extended from 4 cm2 used for performance evaluation to ˜80 cm2 in one unit modular cell (FIGS. 19A to D), which can be further stacked in the future for scaled up capacities. A maximal cell current of over 20 A was achieved, with a high H2O2 selectivity of ˜80% and production rate of ˜0.3 mol/h. Under a fixed cell current of 8 A, the scaled-up device is also capable of producing highly concentrated pure H2O2 solutions up to 20 wt. % under a DI flow rate of 5.4 mL h-1 (FIG. 19D and FIG. 16B).

As demonstrated above, an electrosynthesis cell according to one or more embodiments of the present disclosure may produce highly pure, concentrated H2O2 with high current efficiency (95˜95%). Pure oxygen or oxygen in air can be directly reduction into H2O2 at the cathode using an oxidized carbon material. Additionally, water may be oxidized into oxygen at the anode using IrO2/C catalyst. Then, the anode O2 can be feed back to the cathode to produce H2O2 in order to enhance the overall electricality-to-H2O2 efficiency of the device.

High current efficiency towards H2O2 (˜90%) even at very high current density (>200 mA/cm2) can be obtained by the present electrosynthesis cell and corresponding process. A pure ˜1.6 wt % H2O2 can be continuously produced under a constant DI flow-rate of 27 mL min−1.

A 70-hour continuous and stable production of ˜0.13 wt % pure H2O2 solution was demonstrated using the carbon catalyst in this solid electrolyte ORR cell. The current density was fixed at 15 mA/cm2 (60 mA cell current) and the DI flow rate of 27 mL h−1, resulting in a total of 1.89 L˜0.13 wt % pure H2O2 product. Over this 80-hour course, the cell voltage showed negligible change, and the H2O2 selectivity was maintained above 99%.

It was also shown that the 4 cm2 device can be easily scaled up to a 100 cm2 unit module for ultra-concentrate pure H2O2 production. A maximal 20 A current can be achieved using the unit module with high H2O2 selectivity (>90%) By simply tuning the flow-rate of the DI water, concentrated H2O2 can be obtained. Specifically, it was shown that commercial-level 3-20 wt % pure H2O2 can be continuously produced using the presently disclosed electrosynthesis cell and process.

Based on the design of porous solid electrolyte layer as well as the good performance of 2e-ORR catalysts, this demonstrated approach for direct electrosynthesis of pure H2O2 solutions, with high production rates, selectivity, and energy efficiencies can applied to a wide variety of electrochemical synthesis techniques of liquid products which are in most cases generated and mixed in liquid electrolytes. The current process and electrolytic cell can be extended beyond H2O2 generation to other applications in electrocatalysis, such as CO2 reduction to pure liquid fuel solutions and N2 reduction to pure ammonia solutions. Future improvements on the intrinsic activity of 2e-ORR catalysts under neutral pH environments will further boost the device energy efficiencies. Earth-abundant catalysts, with similarly high performances in HOR, may also be employed as alternative materials to Pt for large-scale renewable H2O2 generation.

With different solid electrolyte properties, the present design for a three-compartment electrolytic cell device can be further extended to other electrocatalytic synthesis of pure products beyond H2O2, such as CO2 reduction, N2 reduction and so on.

Production of Pure Liquid Fuels Via CO2RR

EXAMPLE 8 Performance of the 2D-Bi Catalyst

The excellent CO2RR performance of the 2D-Bi catalyst as well as its easy scalability provide good preparations for the demonstration of producing pure HCOOH solution in the presently proposed CO2 reduction cell with solid electrolytes. IrO2—C on the anode side was selected as very stable and active OER catalyst in acidic solutions, which can help to release H+ from water to compensate for the negative charges of generated HCOO.

FIG. 20A plots the CO2RR activity of 2D-Bi//solid-electrolyte//IrO2—C cell with different types of solid ion-conductors. In the case of H+ conductor, the overall current density can reach to over 100 mA/cm2 at a cell voltage of 3.27 V, while the HCOO conductor delivers a relatively lower current of 50 mA/cm2 at ca. 3.47 V. No other liquid products were observed except HCOOH by 1H and 13C NMR. In the cell with H+ conducting solid electrolyte, a peak HCOOH FE of 93.1% with a partial current of 32.1 mA/cm2 was achieved under 3.08 V (FIG. 20B), corresponding to 0.112 M pure HCOOH solution under a DI flow-rate of 12 mL h-1 (with electrode geometric area of 4 cm2). The pH of this produced HCOOH solution was measured to be ca. 2.3˜2.4, which agrees well with the theoretical pH value of 0.112 M pure HCOOH solution (pH=2.36). Furthermore, negligible amounts of impurity ions including potassium, sodium, iron, bismuth, sulfur (all lower than 100 ppm) and iridium (lower than 10 ppb) were detected by inductively coupled plasma atomic emission spectroscopy (ICP-OES). The pH and ICPOES results demonstrate the ultra-high purity of the produced HCOOH solution by the electrosynthesis device. Under this maximal HCOOH selectivity, an impressive energy conversion efficiency of 42.3% from electricity to pure HCOOH was delivered.

In addition, a similar peak HCOOH FE of 90.1% with a HCOOH partial current of 28 mA/cm2 was obtained at 3.21 V using a HCOO conductor (FIG. 20C), demonstrating the generality of the solid-state electrolyte concept for pure HCOOH solution production. Importantly, it was shown that the concentration of pure HCOOH solution can be easily controlled by tuning the flow-rate of DI stream (FIG. 20D). By slowing down the DI flow, higher HCOOH concentration of 6.73 M (˜29 wt %) was achieved in CO2-to-HCOOH conversion with a FE of 30%. The decreased HCOOH FEs with increased HCOOH concentrations might be due to two reasons: the concentrated HCOOH solution in the solid electrolyte channel 1) may thermodynamically lower the CO2-to-HCOOH conversion rate; and 2) can crossover the Nafion film and get oxidized by anode which has been typically observed in direct formate fuel cells 49. It was found that if the Nafion 1110 (254 μm) CEM was used instead of Nafion 117 (183 μm), then a higher HCOOH FE can be achieved. Specifically, an HCOOH FE of 40.3% was obtained at 100 mA/cm2 under 0.6 mL h-1 DI rate for Nafion 117, while 51.1% HCOOH FE is achieved for Nafion 1110 under the same condition. It is also worthwhile to note that the improvement of HCOOH FE is still limited even when a thicker CEM (254 vs. 183 μm) was employed to block the HCOOH crossover. Thus, the concentrated HCOOH solution in the solid electrolyte layer may also thermodynamically lower the CO2-to-HCOOH conversion rate.

A 100-hour continuous and stable production of ˜0.11 M pure HCOOH solution was demonstrated using the 2D-Bi catalyst in this solid electrolyte CO2RR cell (FIG. 21). The current density was fixed at 30 mA/cm2 (120 mA cell current) and the DI flow rate of 16.2 mL h-1, resulting in a total of 1.6 L 0.1 M pure HCOOH product. Over this 100-hour course the cell voltage showed negligible change, and the HCOOH selectivity was maintained above 80%. The water contact angle test unveils the superhydrophobicity of 100-hour aged cathode GDL, demonstrating that no water-flooding occurred. SEM characterization of post-stability catalyst reveals that no Bi particulate agglomerates were observed, further highlighting the advantages of the electrosynthesis cell configuration for long-term stability compared with that in an H-cell. Moreover, higher concentration HCOOH solutions (e.g. >1.0 M) can be stably and continuously obtained. Analysis of the HCOOH in the generated concentrate HCOOH solution (150 mA cell current, 2 mL/h DI flow for 20 hours) leads to an average HCOOH FE of ca. 80.9%, translating to ˜1.13 M HCOOH. In addition, besides the polymer solid electrolyte, it was further shown that an inorganic solid proton conductor, like insoluble CsxH3-xPW12O40, can also be employed for pure HCOOH generation, significantly expanding the application range of solid electrolyte design.

EXAMPLE 9 Extension to Other Products

In accordance with one or more embodiments of the present disclosure, other types of electrolyte-free CO2RR liquid products can be obtained using this porous solid electrolyte cell design.

To demonstrate its wide applicability for other pure liquid fuel productions beyond HCOOH, a Cu catalyst was selected, which can generate multiple C2+ oxygenate fuels. Based on the Cu catalyst derived from commercial Cu2O nanoparticles, it was found that electrolyte-free dense C2+ oxygenate fuels, including ethanol, acetic acid, and n-propanol can be efficiently collected (FIG. 20E). At 3.45 V, the electrolyte-free oxygenates solution was obtained containing 4.6 mM ethanol, 3.4 mM n-propanol and 1.3 mM acetic acid.

The GC and NMR results present an overall ca. 100% FE, indicating that all the generated liquid fuels have been successfully collected by the DI stream. The above discussion confirms that the solid electrolyte cell design can be easily extended to produce other pure liquid fuels such as pure ethanol solutions once highly selective and exclusive CO2RR catalyst is developed.

Experiment 10: Electrocatalytic Hydrogenation to Pure Vapor

Here the electrocatalytic CO2 hydrogenation to pure HCOOH vapor under ambient conditions is demonstrated based on the solid state electrolyte design, which excludes the OER process without any liquid streams involved.

As illustrated in FIG. 22A, hydrogen was electrochemically oxidized into proton at the anode, which is catalyzed by commercial Pt/C, whereas the CO2 gets reduced into formate at cathode using the 2D-Bi. The electroreduced HCOO ions will recombination with the generated protons, which across from the hydrogen oxidation reaction (HOR) side, to form pure HCOOH. Then, the formed HCOOH vapor at the solid electrolyte surface will be brought out by the continuous humified N2 flow. Of note, no liquid stream was required for entire cell, leading to an all vapor phase operation. This solid electrolyte electrochemical cell can offer a 100% atom utilization without byproduct for HCOOH production using CO2 and H2 as feedstocks (CO2+H2→HCOOH). FIG. 22B displays the current-voltage profile of the direct electrocatalytic CO2 hydrogenation cell for HCOOH vapor generation. A peak HCOOH FE of 83.3% was obtained at only 1.1 V.

An HCOOH partial current of 163 mA cm−2 (HCOOH FE of 73.3%) can be achieved at low cell voltage of mere 1.33 V. It is important to mention that the formed HCOOH can be detected at as low as 0.45 V, translating to a small cell overpotential of only 0.26 V.

Given the wide variety of solid electrolytes, as well as different liquid fuels from CO2RR or many other electrocatalytic reactions, we demonstrate a general approach using solid electrolyte design in generating pure liquid product solutions or vapors in electrocatalysis.

Electrocatalytic Characterization of TM-CNT Catalyst

EXAMPLE 11 Electrocatalytic Characterization of Single Atom TM-CNT Catalyst

The ORR performances of TM-CNT as prepared in Example 2 were further evaluated in 0.1 M KOH by casting a thin catalyst layer onto rotation ring disk electrode (RRDE), with the collection efficiency pre-calibrated by the redox reaction of [Fe(CN6)]4/[Fe(CN6)]3.

The potential of the reference electrode was double confirmed by purging pure H2 gas onto a physically and electrochemically polished polycrystalline Pt wire or Pt rotation disc electrode at a reasonable rotation speed. The ORR peak of Fe-CNT was observed in the cyclic voltammetry in O2-saturated electrolyte, in contrast with the double layer current when O2 was switched to N2. FIG. 23A shows the polarization curves of M-CNTs for their performance screening at a constant catalyst loading of 0.1 mg cm−2, together with the H2O2 generation current detected by the Pt ring electrode. Note that the possible H2O2 decomposition on metal oxides compared to the generation should be negligible. The corresponding H2O2 selectivity and electron transfer numbers were plotted in FIG. 23B as a function of potential.

Among the prepared different TMs, Fe-CNT presents the strongest H2O2 generation performance evaluated by RRDE, with a maximal H2O2 selectivity of more than 95%, and a high potential of 0.822 V vs. RHE to deliver a 0.1 mA cm−2 H2O2 onset current, as showin in FIG. 23B. This early onset is superior to the so-far reported H2O2 catalysts such as Pd—Hg, Au—Pd, Pt single atoms, and highly oxidized CNTs, representing a facile ORR kinetics with negligible overpotential for O2-to-H2O2 conversion.

By switching the metal dopants from Fe to Pd, Co, and Mn, the H2O2 selectivity was changed to 90.3, 74.8, and 39.8%, respectively, suggesting a wide range tuning of electron transfer numbers from 2.09 to 3.20. FIGS. 24A-B show the effects of Fe atom loading at respective amounts of 0, 0.05, 0.1, and 0.2 at % on H2O2 activity and selectivity. Compared to bare CNT, the performance was gradually increased with the increase of Fe atom loading, but dramatically dropped once Fe clusters was formed demonstrating the critical role of atomically dispersed Fe.

Fe-CNT maintains its high H2O2 selectivity and activity when applied onto a GDL (FIG. 25A) electrode with facilitated O2 mass diffusion for large current densities in electrolyzer, where the colorimetric quantification of H2O2 was employed instead. In 1 M KOH, the catalyst delivered a steady-state H2O2 partial current of 43 mA cm−2 at 0.76 V with a Faradaic efficiency of 95.4%, corresponding to a H2O2 production rate of ˜1.6 mol g−1h−1 or 8 mol m−2h−1 (FIG. 25B).

The catalytic activity of Fe-CNT in both RRDE test and bulk electrolysis presents significant improvements compared to conventional catalysts. The performance stability of Fe-CNT single atom catalyst was also demonstrated on RRDE in FIG. 23C, with a stable H2O2 selectivity of above 90% over the 8-h continuous operation. Post-catalysis XAS analysis of Fe K-edge XANES overlaps well with that of pristine Fe-CNT, suggesting that the electronic structure and coordination of Fe single atoms remains unchanged as demonstrated in FIG. 26A. The corresponding Fourier transformed EXAFS spectrum (FIG. 26B) of post-catalysis Fe-CNT reveals that Fe atoms still maintain an atomic dispersion. The reaction pathway can also be tuned by maintaining the metal center while switching its neighboring metalloid coordination, which combined with the corresponding changes in catalytic performances, could further reveal the possible active coordination motifs for H2O2 generation. The H2O2 selectivity of Fe-CNT was decreased to a maximum of 60% when the catalyst was annealed in forming gas with Fe—C—O coordination reduced (Red. Fe-CNT); the 4e ORR pathway was preferred when O was replaced with N to form Fe—C—N coordination, with the electron transfer number boosted from 2.09 of Fe-CNT to 3.71 of Fe-N-CNT, and even to 3.90 when the mass loading was increased to a typical fuel cell test condition.

EXAMPLE 12 Water Disinfection by FT-CNT Catalyst

In the following Example, Fe-CNT catalyst were employed in a prototype Example to test the catalyst's disinfection effectiveness. Neutral pH was used instead of alkaline solutions to mimic the practical applications, therefore the ORR selectivity of Fe-CNT was first evaluated in 0.1 M PBS electrolyte using RRDE as shown in FIGS. 27A and 27B. H2O2 generation started at ˜0.53 V and maintained a high selectivity above 90% from 0.5 to 0.3 V. The practical electrolysis was performed in an H-cell where Fe-CNT catalyst was casted onto a GDL electrode (0.5 mg cm−2 catalyst loading), with the catalytic performance plotted in FIG. 27C. The potential to deliver a 20 mA cm−2 constant current for H2O2 generation remained unchanged over the course of electrolysis (FIG. 27D). Around 1613 ppm H2O2 was generated within 210 min electrolysis as determined by the colorimetric quantification method, representing an average Faradaic Efficiency of 90.8%.

With those performance metrics obtained, electrolyte with Escherichia coli (E. coli) was then used as a model system at a bacteria concentration of ˜107 colony forming units (c.f.u.) mL−1. The disinfection process was monitored by picking up several droplets during the 20 mA cm−2 chronopotentiometric measurement, followed by serially dilution and spread plating onto LB agar for overnight culture. The calculated killing rate is plotted in FIG. 28. Fe-CNT demonstrates a rapid disinfection efficiency for E. coli, delivering a 43% bacteria inactivation in 5 min and more than 99.9999% in 120 min (equals to a 125 L h−1m2electrode processing rate) with no recovery observed.

These results highlight that the TM single atom coordination motifs can effectively tune the ORR pathways and product selectivity. Among different catalysts examined, Fe—C—O coordination was identified as highly active and selective motif for O2 reduction to H2O2.

Anode Catalyst

EXAMPLE 13 Electrocatalytic Synthesis with NiFe-LDH Anode Catalyst

As discussed, the generation of protons by water oxidation on the anode side is provided in order to produce pure formic acid using the above proposed solid electrocatalytic cell. However, the electrocatalytic water oxidation in acidic solution is challenging. Alternative embodiments of the present application may include a four-component electrosynthesis cell where the SE is separated by a bipolar membrane. In such embodiments, the anode may be prepared by coating a GDL electrode with a nickel iron layered double hydroxide (NiFe-LDH) as the OER catalyst and KOH electrolyte to decrease the catalyst cost and anode overpotential.

As illustrated in FIG. 29A, AEM and CEM were also used to separate catalyst coated GDLs and the porous SSE-50 solid ion conductors. A bipolar membrane was employed to separate the cathode and anode compartments, which dissociates water in into H+ and OH during CO2 reduction.

The generated H+ ions from bipolar membrane can neutralize the negatively charged HCOO in the left solid electrolyte layer to produce pure HCOOH. At the same time, more concentrated KOH can be obtained in the right solid electrolyte layer via ionic recombination of OH and K+. The experimentally measured current-voltage profile and the corresponding HCOOH FE of this four-chamber cell is presented in FIG. 29B. A peak HCOOH partial current of ca. 150 mA cm−2 could be achieved under 3.36 V. More importantly, we successfully collected the pure KOH solution of concentration up to 0.66 M under a DI flow-rate of 16.2 mL h−1 (FIG. 29C), demonstrating the feasibility of our strategy.

Impressively, the cell performance showed no obvious changes during the course of stability test. In future applications, the brine streams can be used as anolyte to drive the chlorine evolution at the anode side to replace the OER. Then, three kinds of valuable pure products (HCOOH, NaOH and Cl2) can be simultaneously generated. Implementation of NaOH, Cl2 and HCOOH production from brine stream and CO2 using our solid electrolyte concept can offer environmentally sound, economic strategies for sustainable desalination and carbon-cycling.

Catalyst Including Non-Metal Dopants

EXAMPLE 14 Carbon Catalyst Comprising Non-Metal Dopants

In the following Example, the trade-off between high activity and high selectivity in carbon materials is tested by introducing non-metal dopants, and to see demonstrate how the induced electronic structural changes can enhance the catalysts' 2e ORR activity under large currents while maintaining high selectivity towards H2O2. In this Example, a series of nonmetal dopants, including but not limited to boron, nitrogen, phosphorous and sulfur, were anchored on carbon black substrates, and the result catalysts were compared together with H2-annealed pristine carbon black (Pure C) as the control sample. Samples were prepared in accordance with methods described above.

Among all the materials, boron-doped carbon (B-C) showed the best intrinsic activity while maintaining high selectivity in both alkaline and neutral conditions from rotation ring-disk electrode (RRDE), as show in FIGS. 30C-D, with a positive onset of 0.79V and 0.42V (vs. RHE) in 0.1M KOH and 0.1M Na2SO4, respectively (FIGS. 30A-B).

FIGS. 31A-B show I-V curve data plots for Pure C, B-C and O-C in 1M KOH and 1M Na2SO4, respectively. FIGS. 31C-D further show FE and H2O2 partial currents measured in 1M KOH and 1M Na2SO4. Note that all the I-V curves and faradaic efficiency were taken average of 2˜3 independent tests for each of the samples. For the large current performance in a three-electrode flow cell, B-C showed improved kinetics compared to oxidized carbon (O—C), while maintaining comparably high selectivity in contrast to Pure C, in both alkaline and neutral electrolytes.

Furthermore, as demonstrated in FIGS. 32A-C, the B-C sample is shown to efficiently generate pure H2O2 production using the three-compartment solid-electrolyte cell configuration demonstrated above. The boron doped sample can achieve a high faradaic efficiency (FE) of over 87% within a broad potential window until the current density reaches as high as 400 mA cm−2, as shown in FIG. 32A. A high production rate of 7.36 mmol cm−2h−1 was achieved at 500 mA cm−2 (FIG. 32B) and the cell is capable of operating for 30 hours without performance decay (FIG. 32C).

CEM-CEM Three Component Cell

EXAMPLE 15 Dual CEM in Three Component Electrosynthesis Cell

In the following Example, the cathode anion exchange membrane (AEM) as described above was replaced with a CEM for pure H2O2 solution generation, as shown in FIG. 33.

All other parts, except ORR catalysts, were used, unchanged, compared with the previous design. Similarly, independent water and O2 streams were respectively delivered to water oxidation and 2e-ORR catalysts coating gas diffusion layer (GDL) electrodes.

The anode and cathode were sandwiched with CEM layers to avoid flooding by direct contact with liquid water. In the center, a thin porous solid electrolyte layer facilitated ionic conduction of H+ crossing from the anode to cathode with small ohmic losses and a flowing DI water stream was confined to this middle layer that could then dissolve the pure H2O2 product with no introduction of ionic impurities. By tuning the H2O2 generation rate or the DI water flow rate, a wide range of H2O2 concentrations could be directly obtained with no need for further energy-consuming downstream purification.

Similar to above, the O2 from air will be used in the electrochemical reduction into H2O2 at the cathode (Cathode: O2+2e+2H+→H2O2). And the water will be electrochemically oxidized into O2, while simultaneously releasing protons (Anode: H2O−4e−→O2+4H+). The protons, as the electrical carriers, will move across the CEMs and the porous solid-electrolyte layer to compensate the charge. Since the locally generated H2O2 molecules at the CEM and cathode catalyst interface have a relatively high concentration, they will then chemically and/or electro-osmotically diffuse into the middle solid electrolyte layer, and be further carried out by the water flow as pure H2O2 solution streams.

The CEM provides an extremely acidic environment for ORR. The catalyst tested included metal and non-metal doped carbon catalysts to demonstrate this concept. For example, a nitrogen doped carbon supported nickel single atom (Ni—N—C) was used as the catalyst for 2e-ORR in this CEM//solid electrolyte//CEM device. As shown in FIG. 34, the Ni—N—C single atom catalyst can deliver a stable H2O2 Faradic efficiency (FE) of ca. 30% under 20 mA cm−2 at least for 150 hours. The concentration of generated H2O2 stream was ˜560 ppm under 20 mA cm−2 current density. The stable operation of this new all CEM based reactor demonstrates the feasibility of the three-compartment design for pure H2O2 generation. Additionally, other types of carbon catalysts, including but not limited to surface functionalized carbon, such as B-doped carbon, showed good selectivity in generating pure H2O2 solutions (FIG. 35).

While the disclosure has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the disclosure as disclosed herein. Accordingly, the scope of the disclosure should be limited only by the attached claims.

Claims

1. A porous solid electrolyte electrosynthesis cell for direct synthesis of high purity liquid products wherein the electrosynthesis cell comprises:

a cathode compartment including a cathode electrode comprising a gas diffusion layer loaded with a selective reduction reaction electrocatalyst for specific reduction reactions wherein the reduction reactions comprise oxygen reduction reactions, CO2 reduction reactions, CO reduction reactions, N2 reduction reactions, nitrate reduction reactions and nitrite reduction reactions;
an anode compartment including an anode electrode comprising a gas diffusion layer loaded with a catalyst for oxidation reactions;
a solid electrolyte compartment comprising a porous solid electrolyte;
a cation exchange membrane; and
an anion exchange membrane;
wherein the solid electrolyte compartment is separated from the cathode and the anode by the anion exchange membrane and the cation exchange membrane.

2. The porous solid electrolyte electrosynthesis cell of claim 1, wherein the selective reduction reaction electrocatalyst of the cathode is one or more selected from the group of carbon, transition metals, single atom catalysts of transition metals anchored into carbon nanotubes (CNT), an oxide, or chalcogenides thereof.

3. The porous solid electrolyte electrosynthesis cell of claim 2, wherein the selective reduction reaction electrocatalyst of the cathode is one or more selected from the group of oxidized carbon black, Bi, Co, Pd, In, Pb, Sn, and Cu, transition metals, single atom catalysts of transition metals anchored into carbon nanotubes (CNT), an oxide, or chalcogenides thereof.

4. The porous solid electrolyte electrosynthesis cell of claim 1, wherein the selective reduction reaction electrocatalyst of the cathode is a single atom catalysts of transition metals anchored into carbon nanotubes (CNT), and wherein the transition metal is selected from the group consisting of Fe, Pd, Co, and Mn.

5. The porous solid electrolyte electrosynthesis cell of claim 1, wherein the specific oxidation reactions include hydrogen oxidation reactions, water oxidation reactions or other oxidation reactions.

6. The porous solid electrolyte electrosynthesis cell of claim 1, wherein the oxidation reaction catalyst loaded on the anode is as least one or more selected from carbon, Ru, Ir, Pt, Ni, Fe, Ce or a mixture and/or oxide, chalcogenides thereof.

7. The porous solid electrolyte electrosynthesis cell of claim 1, wherein the oxidation reaction catalyst and the selective reduction reaction electrocatalyst loaded on the gas diffusion layers are in close contact with the cation and anion exchange membranes.

8. The porous solid electrolyte electrosynthesis cell of claim 1, wherein the anion exchange membrane is a copolymer of polystyrene and polystyrene methyl imidazolium chloride.

9. The porous solid electrolyte electrosynthesis cell of claim 1, wherein the cation exchange membrane is a perfluorosulfonic acid membrane.

10. The porous solid electrolyte electrosynthesis cell of claim 1, wherein the porous solid electrolyte is selected from an inorganic ceramic solid electrolyte, a polymer/ceramic hybrid solid electrolyte, solidified gel electrolytes, or ion conducting polymers.

11. The porous solid electrolyte electrosynthesis cell of claim 1, wherein the porous solid electrolyte is selected from a group of ion conducting polymers including polymers or copolymers of styrene, acrylic acid, or aromatic polymers.

12. The porous solid electrolyte electrosynthesis cell of claim 1, wherein the porous solid electrolyte is a porous styrene divinylbenzene copolymer consisting of sulfonic acid functional groups for cation conduction, or quaternary amino functional groups for anion conduction.

13. A process for producing high purity and concentrated liquid products through electrocatalytic reaction in an electrosynthesis cell comprising:

a cathode compartment including a cathode electrode comprising a gas diffusion layer loaded with a selective electrocatalyst for selective reduction reactions;
an anode compartment including an anode electrode comprising a gas diffusion layer loaded with a catalyst for oxidation reactions;
a solid electrolyte compartment comprising a porous solid electrolyte, an inlet, and an outlet;
a cation exchange membrane; and
an anion exchange membrane;
wherein a hydrogen gas or water solutions are supplied to the anode to be electrochemically oxidized on the oxidation reaction catalysts;
an oxygen, CO2, CO, or N2 containing gas is supplied to the cathode to be selectively reduced by the selective reduction reaction catalyst;
wherein the solid electrolyte compartment is separated from the cathode and the anode by the anion exchange membrane and the cation exchange membrane and deionized water or N2 gas is supplied to an inlet of the solid electrolyte compartment to flow through the porous solid electrolyte to bring out the generated liquid product.

14. The process of claim 13, where the anode reaction gas or fluid is selected from H2, H2O, or other related reactants.

15. The process of claim 13, where the cathode reaction gas or fluid is selected from O2, CO2, CO, N2, nitrate, nitrite, or other related reactants.

16. The process of claim 13, wherein the selective reduction reaction electrocatalyst of the cathode is one or more selected from the group of carbon, transition metals, single atom catalysts of transition metals anchored into carbon nanotubes (CNT), or an oxide thereof.

17. The process of claim 16, wherein the selective reduction reaction electrocatalyst of the cathode is one or more selected from the group of oxidized carbon black, Bi, Co, Pd, In, Pb, Sn, Cu, transition metals, single atom catalysts of transition metals anchored into carbon nanotubes (CNT), an oxide, or chalcogenides thereof.

18. The process of claim 13, wherein an electric current is passed through the electrosynthesis cell to electrochemically oxidize the hydrogen containing gas or fluid, water solutions, or other reactants.

19. The process of claim 13, wherein an electric current is passed through the electrosynthesis cell to electrochemically reduce the oxygen, CO2, CO, N2, nitrate, nitrite, or other reactant containing gas or fluid.

20. The process of claim 13, wherein the oxidation reaction catalyst loaded on the anode is as least one or more selected from carbon, Ru, Ir, Pt, Ni, Fe, Ce or a mixture and/or oxide or chalcogenides thereof.

21. The process of claim 13, wherein the oxidation reaction catalyst and the reduction reaction electrocatalysts loaded on the gas diffusion layers are in close contact with the cation and anion exchange membranes.

22. The process of claim 13, wherein the porous solid electrolyte is a porous styrene divinylbenzene copolymer consisting of sulfonic acid functional groups for cation conduction, or quaternary amino functional groups for anion conduction.

23. A porous solid electrolyte electrosynthesis cell for direct synthesis of high purity liquid products wherein the porous solid electrolyte electrosynthesis cell comprises:

a cathode compartment including a cathode electrode comprising a gas diffusion layer loaded with a selective reduction reaction electrocatalyst for specific reduction reactions wherein the reduction reactions comprise oxygen reduction reactions, CO2 reduction reactions, CO reduction reactions, N2 reduction reactions, nitrate reduction reactions and nitrite reduction reactions;
an anode compartment including an anode electrode comprising a gas diffusion layer loaded with a catalyst for oxidation reactions;
a solid electrolyte compartment comprising a porous solid electrolyte;
a first cation exchange membrane; and
a second cation exchange membrane;
wherein the solid electrolyte compartment is separated from the each of the cathode and the anode by the first and second cation exchange membranes.

24. The porous solid electrolyte electrosynthesis cell of claim 23, wherein the selective reduction reaction electrocatalyst of the cathode is one or more selected from the group of carbon, transition metals, single atom catalysts of transition metals anchored into carbon nanotubes (CNT), an oxide, or chalcogenides thereof.

25. The porous solid electrolyte electrosynthesis cell of claim 24, wherein the selective reduction reaction electrocatalyst of the cathode is one or more selected from the group of oxidized carbon black, Bi, Co, Pd, In, Pb, Sn, and Cu, transition metals, single atom catalysts of transition metals anchored into carbon nanotubes (CNT), an oxide, or chalcogenides thereof.

26. The porous solid electrolyte electrosynthesis cell of claim 23, wherein the selective reduction reaction electrocatalyst of the cathode is a single atom catalysts of transition metals anchored into carbon nanotubes (CNT), and wherein the transition metal is selected from the group consisting of Fe, Pd, Co, and Mn.

27. The porous solid electrolyte electrosynthesis cell of claim 23, wherein the specific oxidation reactions include hydrogen oxidation reactions, water oxidation reactions or other oxidation reactions.

28. The porous solid electrolyte electrosynthesis cell of claim 23, wherein the oxidation reaction catalyst loaded on the anode is as least one or more selected from carbon, Ru, Jr, Pt, Ni, Fe, Ce or a mixture and/or oxide, chalcogenides thereof.

29. The porous solid electrolyte electrosynthesis cell of claim 23, wherein the oxidation reaction catalyst and the selective reduction reaction electrocatalyst loaded on the gas diffusion layers are in close contact with the first and second cation exchange membranes.

30. The porous solid electrolyte electrosynthesis cell of claim 23, wherein at least one of the first or second cation exchange membranes are a perfluorosulfonic acid membrane.

Patent History
Publication number: 20220259746
Type: Application
Filed: Jul 15, 2020
Publication Date: Aug 18, 2022
Applicant: William Marsh Rice University (Houston, TX)
Inventors: Haotian Wang (Houston, TX), Chuan Xia (Houston, TX)
Application Number: 17/597,633
Classifications
International Classification: C25B 9/19 (20060101); C25B 1/30 (20060101); C25B 1/27 (20060101); C25B 13/05 (20060101);