APPARATUS AND METHOD FOR PRODUCING HYDROGEN PEROXIDE

The present invention is directed to an apparatus for producing hydrogen peroxide, comprising one or more electrochemical cells, the apparatus further comprising at least one electrically conductive porous gas transport layer disposed next to a cathode gas diffusion layer, the gas transport layer being configured to deliver a flow of oxygen-containing gas towards the cathode gas diffusion layer and being configured to collect current, further including water which is configured to flow through the porous gas transport layer.

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Description
FIELD OF THE INVENTION

The present invention relates to an apparatus and a method for producing hydrogen peroxide. The present invention further relates to a system using the apparatus to produce hydroxyl radicals, and to a method of producing the apparatus. More precisely, the present invention relates to an improved apparatus and method that employs oxygen reduction for producing hydrogen peroxide.

BACKGROUND OF THE INVENTION

Hydrogen peroxide (H2O2) is a versatile chemical, used as an oxidant in industries such as pulp and paper, water treatment and agriculture. The on-site production of hydrogen peroxide from readily available compounds is highly attractive for these industries, as it would enable supply independence and would be more sustainable. Electrolysis cells offer unique advantages in generating chemicals in decentralized facilities with the use of electricity as input energy rather than requiring large chemical production plants. Advantages are, among others, the generation of chemicals where and when they are needed, thereby removing the need for transportation and storage, and facilitating the use of energy produced by sustainable means, such as wind power and solar.

Electrochemical production of hydrogen peroxide has strong advantages over the traditional Anthraquinone process that takes place in centralized chemical facilities to produce hydrogen peroxide. The Anthraquinone process involves a large amount of energy, CO2 emissions and chemical waste. Natural gas is the main source of hydrogen in today's anthraquinone plants. Since production is centralized, hydrogen peroxide needs to be transported to the point of use. For economic reasons, hydrogen peroxide is shipped at concentrations typically between 30 and 70%, which is hazardous and poses safety concerns. Once it reaches the point of use, it often needs to be diluted to concentrations <3%.

These concerns are directly addressed by producing the chemical on-site. Electrochemical production can take place using water and oxygen from the atmosphere to form H2O2 and only electricity is required as energy input, meaning that it can be a CO2 emissions-free process when using CO2-neutral electricity. Furthermore, in many applications, low concentrations (below 3 wt %) are needed which means safety concerns can be avoided altogether if the solutions are produced with low concentrations from the beginning.

The electrochemical production of hydrogen peroxide typically relies on selective oxygen reduction. There have traditionally been two main pathways to produce hydrogen peroxide electrochemically depending on the form of ion conductor used.

The first approach has been to use liquid state ion conductors, usually in the form of an alkaline or neutral salt solution, as described for example in “Direct and Continuous Production of Hydrogen Peroxide with 93% Selectivity Using a Fuel-Cell System”, Angewandte Chemie 2003. This approach has led to high efficiency and concentrations for hydrogen peroxide production, but purity is low since it is hard to separate the salts from the generated hydrogen peroxide.

The second approach has been to use a solid state ion conductor, such as a polymer cation exchange membrane, which results in higher purities, but achievable concentrations and efficiencies are usually lower, as described in “Neutral H2O2 Synthesis by Electrolysis of Water and O2”, Angewandte Chemie 2008.

The art known in the membrane electrode assembly field struggled to achieve sufficiently high throughputs, which has a direct impact on size of the electrodes required and in turn cost. The main reason for that is difficulty in simultaneously achieving the three required conditions for electrochemical hydrogen peroxide production: delivering oxygen uniformly across the cathode electrode, collecting current uniformly from the cathode electrode, and at the same time efficiently extracting hydrogen peroxide from the cathode catalyst layer. Approaches in the art focused in operating in the following environments:

Gas-phase oxygen—which has suitable oxygen transport to the electrodes, leading to high current densities, but suffers from difficulties in extracting hydrogen peroxide from the electrodes, which leads to poor faradaic efficiencies. This means that overall throughputs are low.
Dissolved oxygen in water—water helps extract hydrogen peroxide, which results in high faradaic efficiencies, but on the other hand the low solubility of oxygen in water means current densities are low. Overall throughputs of hydrogen peroxide are low.

To overcome this issue of low throughput, approaches in the literature have focused in designing electrochemical cells that operate in mixed phases of gas and liquid, as the ones disclosed in U.S. Patent Application No. 2014/0131217 A1, and U.S. Pat. No. 5,972,196, and EP Patent No. 3,430,182

These approaches involve applying gas in selected spots of the cathode via bubblers or fluidizing media, while keeping the rest or even the entire cathode immersed in water. Generally, in these designs there are areas of the electrode dedicated to current collection, other areas dedicated to gas delivery, and yet other areas dedicated to hydrogen peroxide extraction. Accordingly, while such mixed phase operation has brought some improvements in the form of higher faradaic efficiencies and throughputs, it still presents challenges in effective and uniform current collection, gas application, product flow, and does not efficiently utilize the full area of the cathode, leading to sub-optimal performance and exacerbating degradation. As such, further improvements that address these and other remaining challenges of production of hydrogen peroxide are still needed.

SUMMARY OF THE INVENTION

The present invention addresses the above discussed challenges exhibited by the production of hydrogen peroxide by providing an improved apparatus for producing hydrogen peroxide, an improved system the formation of hydroxyl radicals, a method of producing hydrogen peroxide using the apparatus of the invention and a method of producing the apparatus of the present invention. At least these and other aspects of the invention are described in detail in the appended claims.

More precisely, and as it will be described in more detail in the following, herewith is presented a novel approach for a design of an electrochemical cell, that is tailored to the synthesis of hydrogen peroxide from an electrochemical oxygen reduction reaction. Further, what is described is the use of a porous electrically conductive layer that simultaneously provides uniform oxygen gas flow and electrical conductivity to the cathode of a hydrogen peroxide producing electrochemical cell. Water is set to flow through the cathode gas diffusion layer, which helps in the removal of hydrogen peroxide from the electrode.

As mentioned above, a second approach has been to use a solid state ion conductor, such as a polymer cation exchange membrane, which results in higher purities. Further in this document it will be shown that the present invention, whereby proposing that a polymer cation exchange membrane be used in combination with a cathode and anode electrode that are in intimate contact with the membrane, forming a single mechanical entity that is known as membrane electrode assembly, leads to higher purities for the resulting hydrogen peroxide but at higher achievable concentrations and efficiencies of conversion than what is known from the art.

The design proposed herewith for the electrochemical cell for the production of hydrogen peroxide of the present invention improves current collection and gas delivery, while at the same time facilitating hydrogen peroxide extraction from the cathode through the presence of water or a forced water flow. This optimizes utilization of the available electrode area, which results in higher throughputs, higher faradaic efficiencies and longer electrode lifetime. Other benefits are a low high frequency resistance (HFR), as well as a very homogeneous distribution of current collection over the whole electrode area.

An apparatus according to a first aspect of the present invention comprises at least one and preferred a plurality of neighboring electrochemical cells, each electrochemical cell comprising an electrode assembly comprising at least one cathode gas diffusion layer, at least one cathode catalyst layer, at least one ion exchange membrane, at least one anode catalyst layer, and at least one anode current collector, the at least one cathode catalyst layer, the at least one ion exchange membrane and the at least one anode catalyst layer being disposed neighboring each other within the electrode assembly, being disposed in succession along an horizontal axis of the membrane electrode assembly, the apparatus further comprising at least one gas transport layer disposed neighboring the cathode gas diffusion layer, the gas transport layer being capable of facilitating a flow of oxygen-containing gas towards the cathode gas diffusion layer and being capable of current collection, the cathode gas diffusion layer comprising water.

A system according to another aspect comprises the apparatus in accordance with the present invention according to any of its aspects discussed herein, and a device facilitating the combination of hydrogen peroxide generated by the apparatus and ultra-violet light or ozone to facilitate the formation of hydroxyl radicals.

A method of producing hydrogen peroxide using the apparatus of the present invention, according to yet another aspect of the present invention and a method of producing the apparatus of the present invention are also discussed herewith in detail.

Other aspects of the invention are captured in the dependent claims.

In summary, the present invention proposes at least incorporating an electrically conductive porous gas transport layer that simultaneously collects current from the cathode, and uniformly delivers oxygen gas to the cathode, while at the same time having water present in the cathode gas diffusion layer. This configuration maximizes the electrode surface utilized for hydrogen peroxide generation, and facilitates extraction of the generated hydrogen peroxide, resulting in improved performance compared to the configurations already known from the art.

Such an apparatus enables the generation of hydrogen peroxide at the point of use, using only readily available substances such as oxygen (from the air), and water. This has numerous advantages over purchasing bulk hydrogen peroxide, including supply security, CO2 neutrality and safety.

BRIEF DESCRIPTION OF THE DRAWINGS Reference List

    • 1 electrochemical cell
    • 2 cathode plate
    • 3 gas transport layer
    • 4 electrode assembly
    • 5 anode chamber
    • 6 gas inlet
    • 7 cathode water inlet
    • 8 cathode water, oxygen and peroxide outlet
    • 9 anode water inlet
    • 10 anode water output
    • 11 cathode water inlet
    • 12 cathode water outlet
    • 13 gas diffusion layer
    • 14 catalyst layer
    • 15 membrane
    • 16 catalyst layer
    • 17 anode current collector
    • 18 cathode end plate
    • 19 cathode current collector
    • 20 additional gas diffusion layer
    • 21 anode gasket
    • 22 anode end plate
    • 23 Water pump cathode
    • 24 Gas/oxygen pump
    • 25 Cathode water, oxygen and hydroxide peroxide
    • 26 Water pump anode
    • 27 Anode water and oxygen outlet
    • 28 Power supply
    • 29 Hydrogen peroxide sensor

In the following the present invention will be described as well in connection with the here appended drawings, where:

FIG. 1 is a schematic representation of a portion of the apparatus of the present invention, exhibiting an electrically conductive porous gas transport layer along with components of a membrane-electrode assembly, in accordance with an embodiment of the present invention.

FIG. 2 is a schematic view of a design for an electrochemical cell, in accordance with another embodiment of the present invention.

FIG. 3 is a further schematic view of a configuration for an electrochemical cell design, in accordance with yet another embodiment of the present invention.

FIG. 4 is an exploded view of the electrochemical cell design of FIG. 1.

FIG. 5 is a flow representation of a method for making hydrogen peroxide while employing the apparatus of the present invention.

The figures depict various embodiments of the present disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following discussion that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles described herein.

DETAILED DESCRIPTION OF THE INVENTION

The following description is presented to enable one of ordinary skill in the art to make and use the disclosed subject matter and to incorporate it in the context of particular applications. Various modifications, as well as a variety of uses in different applications will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to a wide range of embodiments. Thus, the present disclosure is not intended to be limited to the embodiments presented, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

In the following detailed description, numerous specific details are set forth in order to provide a more thorough understanding of the present disclosure. However, it will be apparent to one skilled in the art that the present disclosure may be practiced without necessarily being limited to these specific details. In other instances, well-known structures and devices are shown in block diagram form, rather than in detail, in order to avoid obscuring the present disclosure.

All the features disclosed in this specification, (including any accompanying claims, abstract, and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

As used here, the phrase “electrochemical cell,” refers to, for example, a device that includes at least a positive electrode, a negative electrode, and an electrolyte therebetween which conducts ions (e.g., H+) but electrically insulates the positive and negative electrodes. In some embodiments, the device may include multiple positive electrodes and/or multiple negative electrodes enclosed in one container.

As used here, the phrase “positive electrode,” refers to the electrode from which positive ions, e.g. H+, conduct, flow or move. As used herein, the phrase “negative electrode” refers to the electrode towards which positive ions, e.g., H+, flow or move during discharge of the electrochemical cell.

Alternatively, the application of heat and pressure ensures that the cathode and membrane are physically attached and the anode and the membrane are physically attached.

As used here, the phrase “electrolyte”,” refers to an electrolyte in the form of a cation exchange membrane, for example Nafion, which allows ions, e.g., H+, to migrate there through but which does not allow electrons to conduct therethrough

As used here, the phrase “directly contacts,” refers to the juxtaposition of two materials such that the two materials contact each other sufficiently to conduct either an ionic or electronic current. As used herein, “direct contact” refers to two materials in physical contact with each other and which do not have any third material positioned between the two materials which are in direct contact.

As used herein the term “porous,” refers to a material that includes pores, e.g., nanopores, mesopores, or micropores.

As used herein the term “making,” refers to the process or method of forming or causing to form the object that is made. For example, making an energy storage electrode includes the process, process steps, or method of causing the electrode of an energy storage device to be formed. The end result of the steps constituting the making of the energy storage electrode is the production of a material that is functional as an electrode.

As used herein, the phrase “providing” refers to the provision of, generation or, presentation of, or delivery of that which is provided.

As used herein the term “solvent,” refers to a liquid that is suitable for dissolving or solvating a component or material described herein. For example, a solvent includes a liquid, e.g., toluene, which is suitable for dissolving a component, e.g., the binder, used in the garnet sintering process.

As used herein, the terms “water oxidation reaction” refer to a reaction such as


2H2O→O2+4H++4e−

This reaction takes place at the anode.
Alternative anode reactions include water oxidation to hydrogen peroxide or ozone, hydrogen oxidation or oxidation of alcohols.

As used herein, the terms “oxygen reduction reaction” refer to a reaction such as


2O2+4H++4e−→2H2O2

This reaction takes place at the cathode.
Oxygen sources include air, oxygen generated on site (for example through a pressure swing adsorption system), and oxygen gas cylinders.

Other definitions apart from the ones specified in the section above may be found through this document.

The apparatus of the present invention comprises a plurality of electrochemical cells, each electrochemical cell 1 comprising at least an electrode assembly 4. The electrode assembly 4 may be a membrane electrode assembly. The membrane electrode assembly comprises electrodes at which electrochemical reactions take place. The membrane electrode assembly comprises in its most general configuration of an anode, a cation exchange membrane, and a cathode that are in contact with each other. Distinct from configurations known from the art, in the configuration proposed by the present invention, no porous ionically conductive layer is present between the cation exchange membrane and cathode.

The anode acts as a proton source for the cathode, and while water is the most common electrolyte reactant, other electrolytes (proton sources) such as alcohols (e.g. methanol, ethanol) or molecular hydrogen are envisioned to be used in accordance with the present invention. If alternative proton sources to water are used, the overall cell reaction and half-cell reaction are modified as needed.

Anodes for water oxidation to oxygen are well-known to those versed in the art. These typically consist of iridium oxide nanoparticles deposited directly on a polymer exchange membrane or a current collector, forming the anode catalyst layer 16.

The ion exchange membrane 15 or polymer exchange membrane 15 should be a proton conducting membrane, exemplarily a Nafion™ ion exchange membrane. The thickness of the membrane is between 10 μm to 1500 μm, preferably between 100 and 500 μm.

The anode current collector 17 may comprise a Titanium layer or a Titanium felt, with thickness ranging from 50 μm to 3000 μm. The layer or felt comprises porosity to allow an escape path for the oxygen gas generated at the anode catalyst layer 16. The sintered Titanium layer or Titanium felt can also be coated with other materials, such as Platinum or Gold, to improve electrical contact. Iridium oxide nanoparticles can be combined or replaced with ruthenium oxide, platinum and other metals. Deposition of the nanoparticles occurs via spray coating, tape casting and other suitable methods, and it can take place directly at the polymer exchange membrane 15, forming a catalyst coated membrane (CCM) 15 or at the current collector 17, forming a GDE. Following the deposition step, the polymer exchange membrane 15 and the sintered Titanium layer or Titanium felt 17 can be attached to each other in a manner that the anode catalyst layer 16 is located in between. The attachment can be mediated by the application of ionomer solution, and the application of heat and/or pressure.

It is the cathode that reduces the oxygen into hydrogen peroxide. The oxygen may be sourced from air, an oxygen concentrator or from a cylinder of compressed gas.

Cathodes consist of a cathode catalyst layer 14 and a cathode gas diffusion layer 13, layers 13 and 14 are in contact with each other. The cathode gas diffusion layer 13 is porous and made of an electrically conducting material to enable transport of oxygen, water and hydrogen peroxide to/from the cathode catalyst layer 14. The cathode gas diffusion layer 13 consists of carbon cloth or fibers. Other suitable cathode gas diffusion layers include metallic foams or meshes, for example made of Titanium or other metals, or other electrically conductive foams such as reticulated vitreous carbon (RVC) or graphene oxide. The thickness of the cathode gas diffusion layer is between 0.05 mm to 10 mm, preferably between 0.1 to 5 mm, even more preferably between 0.5 to 2 mm. The cathode gas diffusion layer 14 can be coated on either one or both sides with PTFE or other materials, to modify its properties.

The cathode catalyst layer 14 contains the catalyst where the electrochemical reaction takes place, and it is placed between the cathode gas diffusion layer 13 and the ion polymer exchange membrane 15. A catalyst ink may be deposited onto the cathode gas diffusion layer 13, forming a gas diffusion electrode. The catalyst ink contains ionomer and a catalyst, mixed with a solvent. Typical ionomers include Nafion dispersion. Solvents include alcohols and/or water. Cathode catalysts should be selective towards oxygen reduction to hydrogen peroxide, and include Pt—Hg, Pd—Hg, Cu—Hg, Ag—Hg, Ag, Au, carbon, graphene, nitrogen doped carbon, sulphur doped carbon, cobalt porphyrins and phthalocyanines, transition metal sulfides and nitrides and any combinations thereof. Catalyst materials are in a nanoparticle form in order to increase surface area and facilitate deposition procedures.

In an alternative embodiment, catalyst ink is sprayed directly on the polymer exchange membrane, forming a catalyst coated membrane, with the gas diffusion layer added afterwards. It is also possible to combine both a catalyst coated membrane and a gas diffusion electrode.

In the electrochemical cell 1 comprising the electrode assembly 4, the cathode is placed with its catalyst layer 14 facing the ion polymer exchange membrane 15. In a possible embodiment it is the application of heat and pressure that ensures that the cathode and membrane are physically attached. The same is valid for the application of heat and pressure for ensuring the attachment between the anode and the membrane. Typical values for temperature and pressure are 80-130 C, and 20-2000 kg/cm2, which are usually maintained from 2 to 20 minutes. Alternatively, a binder material may be used to ensure the attachment of these layers.

The anode current collector 17 may also be pressed or bound with a binder on the opposite side of the membrane 15 in a single-step pressing. The result is a single mechanical entity containing cathode and anode electrodes, as well as a polymer exchange membrane. The entity is the membrane-electrode assembly (MEA) or the electrode assembly 4.

The electrode assembly 4 is mechanically assembled in an electrochemical cell 1, which provides the right environment in terms of current collection, gas and water delivery and peroxide extraction. The components of the electrode assembly 4 and a gas transport layer 3 that is also comprised by the apparatus of the present invention as assembled are shown in the figures and discussed in more detail in connection with the figures. The gas transport layer 3 must be both electrically conductive, and porous.

The electrochemical cell 1 in accordance with an embodiment of the present invention comprises a configuration as follows: an electrically conductive porous gas transport layer 13, placed in direct contact with the cathode side of the membrane-electrode assembly 4, and serves the dual purpose of both providing a uniform flow of oxygen-containing gas throughout its surface, as well as serving as a current collector. The electrically conductive porous gas transport layer 13 could be made by either one of aluminum, titanium, graphite, other metals or post-transition metals. In order to provide a uniform gas flow, the porosity of the electrically conductive porous gas transport layer 13 should be adapted to overall gas flow and gas pressure. Preferred pressure drop across the electrically conductive porous gas transport layer is of at least 1 mbar, and preferably above 20 mbar, and even more preferably above 30 mbar. Thickness of the electrically conductive porous gas transport layer is between 0.5 and 10 mm, preferably between 1 and 5 mm and even more preferably between 1 and 3 mm. Pore size of the electrically conductive porous gas transport layer is between 0.1 and 100 um, preferably between 0.13 and 10 um, and even more preferably between 0.2 and 5 um. The electrically conductive porous gas transport layer should cover at least 10% of the cathode surface, preferably at least 70% and even more preferably at least 95%.

Oxygen-containing gas flows to the cathode side of the electrode assembly 4 through the porous gas transport layer 3, going through the cathode gas diffusion layer 13 in the through-plane direction and reaches the cathode catalyst layer 14. Water flows through the cathode gas diffusion layer 13 in its in-plane direction. In this manner, the cathode has simultaneous access to oxygen containing gas, water, and electricity. The hydrogen peroxide generated at the cathode is dissolved in the flowing water, and is pushed out of the cathode catalyst layer 14. As a result, hydrogen peroxide decomposition is minimized and faradaic efficiency and throughput are improved. The electrically conductive porous gas transport layer 3 provides important advantages on cell assembly and repeatability over previous designs that relied on gas dispersers, where a single gas disperser that is not assembled properly or is outside of the required tolerance could lead to cell failure. In addition, another advantage is that the electrically conductive porous gas transport layer serves the dual purpose of collecting current from the cathode electrode, as well as delivering the oxygen gas reactant to the cathode electrode, while gas dispersers would typically only disperse the gas and additional components would be required for current collection.

In accordance with another embodiment of the present invention, at least one additional gas diffusion layer 20 is inserted between the cathode gas diffusion layer 13 and the electrically conductive porous gas transport layer 3, to facilitate water or gas transport, or favor hydrophilicity or hydrophobicity. The first and last of the inserted gas diffusion layers are in contact with the electrically conductive porous gas transport layer 3 and the cathode, respectively. Preferably, the gas diffusion layer 13 adjacent to the electrically conductive porous gas transport layer 3 is of hydrophobic nature. The gas diffusion layers could also be patterned with Teflon or other substances to have select preferential areas of hydrophobicity. These preferred hydrophobicity areas could be in-plane, or through-plane or both of the gas diffusion layer. In addition, any inserted gas diffusion layers could cover an area of at least 10% of the cathode, preferably at least 70% and even more preferably at least 95%.

A cathode plate is placed on the side of the electrically conductive porous gas transport layer 3 opposite of the electrode assembly 4. Its role is to provide mechanical support and electrical contact to the electrically conductive porous gas transport layer 3 and the membrane electrode assembly 4. The cathode plate is made of an electrically conductive material, such as aluminum, titanium, stainless steel or graphite. A combination of injection molded plastic and conductive material is also suitable for the cathode plate. The cathode plate may have a dedicated gas inlet, and gas is directed to an internal cavity from which is homogeneously delivered to the electrically conductive porous gas transport layer 3. Similarly, the cathode plate also contains liquid inlets and outlets. Water enters in the inlet, and water together with generated hydrogen peroxide and any excess gas comes out of the outlet. Water entering through the inlet could contain dissolved air or oxygen, or nanobubbles, which act as additional reactant for the cathode reaction. Importantly, and differently from other references known in the art, water should flow in-plane through the cathode gas diffusion layer 13 to facilitate hydrogen peroxide removal from the cathode.

In some embodiments of the present invention, the cathode plate and electrically conductive porous gas transport layer 3 have inlets and outlets in the through-plane direction constituting internal manifolds.

In order to facilitate current collection from the electrically conductive porous gas transport layer, the cathode plate gas cavity could have electrically conductive pillars, a coarse porous material or a mesh, that are in direct contact with the electrically conductive porous gas transport layer 3.

In accordance with another embodiment of the present invention, gas and liquid inlets and outlets can be incorporated in respective gaskets without affecting the nature of the invention. Suitable gasket materials include PTFE, EPDM and other polymer-based substances, as well as ABS, PA and other plastics.

In a further embodiment of the present invention, the electrically conductive porous gas transport layer could be physically attached to the cathode housing, by means for example of soldering or welding. In some other embodiments, the electrically conductive porous gas transport layer 3 and the cathode housing are simply pressed against each other during assembly. An O-ring, gasket or sealant products can be used between the two in order to prevent gas leakage.

An anode chamber, collecting electrical current from the electrode assembly, and contains the inputs and outputs to the anode side of the electrode assembly may also be part of the apparatus of the present invention. The anode chamber contains an anode input and an anode output. The anode input serves to introduce water inside the anode chamber, and the output directs excess water not consumed by the anode and oxygen gas generated during the electrochemical reaction outside of the housing. The anode chamber may be in electrical contact with the anode side of the electrode assembly 4. This can be facilitated by pillars or other structures that allow water flow through, while at the same time being in direct contact with the anode. In other embodiments, porous metals or mesh structures could also be used as a separate component.

The components of the cell are put together, and kept in place through bolts, clamps, or other tools.

In accordance with yet other embodiments of the present invention, the cathode and anode plates may be treated as a single piece, a bipolar plate.

Once the electrochemical cell is assembled, the required reactants and power are delivered to the electrochemical cell.

Following assembly of the electrochemical cell 1 into the housing, oxygen-containing gas is introduced at the cathode with a flow between 0.01 to 100 mL/min/cm2 of electrode area, to obtain a pressure between 0.01 and 10 bar. The source of oxygen-containing gas may be one of ambient air, a pressurized oxygen bottle or an oxygen concentrator. Water is introduced to the anode with a water flow between 0.01 to 50 ml/min/cm2 of electrode area. Preferably the water used is deionized, with a conductivity under 20 μS/cm, and even more preferably with a conductivity under 1 μS/cm. This flow can be continuous or pulsating so as to only refill the anode compartment periodically. Water is also introduced at the cathode chamber in a suitable flow, typically between 0.01 to 50 ml/min/cm2 of electrode area. Voltage is applied between the cathode and anode electrodes, between 0.6 and 10 V per cell, preferably between 1.2 and 5 V and even more preferably between 1.2 and 3.5 V. Current from the cell ranges between 20 mA/cm2 to 1500 mA/cm2. This results in hydrogen peroxide being generated at the cathode. The generated concentration is between 200 mg/L to 200000 mg/L, preferably between 1000 to 30000 mg/L. The output concentration can be varied depending on the applied current and the water flow in the cathode chamber. It is also possible to combine one or more cells in series, in parallel or a combination of both to generate higher throughputs.

The generated hydrogen peroxide solution can be stored in a reservoir for subsequent use or be directly injected in a pipe. Examples of suitable uses are within wastewater treatment, irrigation water treatment or cooling tower water treatment, or any other applications where hydrogen peroxide is used as an oxidant, biocide and/or oxygen source. Generated hydrogen peroxide can also be combined with UV light, Fenton-like agents (such as iron ions) or ozone to create OH radicals, which have a higher oxidation potential and are the basis for advanced oxidation processes. It can also be combined with acetic acid on-site to generate peracetic acid. Several of the electrochemical cells in this configuration can be arranged in parallel or series, which would enable a higher overall throughput. A particularly attractive arrangement is a series connection between cell in a compact fashion, also called a stack or stacking.

Therefore to summarize at least some of the aspects of the present invention discussed above, the present invention is directed, according to one of its embodiments, to an apparatus for producing hydrogen peroxide, comprising a plurality of neighboring electrochemical cells 1. Each electrochemical cell 1 comprises an electrode assembly 4 comprising at least one cathode gas diffusion layer 13, at least one cathode catalyst layer 14, at least one ion exchange membrane 15, at least one anode catalyst layer 16, and at least one anode current collector 17. The at least one cathode catalyst layer 14, the at least one ion exchange membrane 15 and the at least one anode catalyst layer 16 are disposed neighboring each other within the electrode assembly 4, being disposed in succession along an horizontal axis of the membrane electrode assembly 4. The electrochemical cell 1 also comprises at least one electrically conductive gas transport layer 3 disposed neighboring the cathode gas diffusion layer 13, the gas transport layer 3 being capable of facilitating a flow of oxygen-containing gas towards the cathode gas diffusion layer 13 and being capable of current collection. In accordance with one embodiment of the present invention, the cathode gas diffusion layer 13 contains water, which is preferably flowing.

The cathode catalyst layer 14 comprised by the apparatus of the present invention comprises one or a plurality of catalysts, and the anode catalyst layer 16 comprised by the apparatus of the present invention comprises as well one or a plurality of catalysts.

In accordance with an embodiment of the present invention, in the membrane electrode assembly 4 a first side of the ion exchange membrane 15 is bound against a second side of the cathode catalyst layer 14 and the anode catalyst layer 16 is bound against a second, opposing side of the ion exchange membrane 15.

In accordance with an embodiment of the present invention, at least one gas transport layer 3 is an electrically conductive porous gas transport layer 3 that is in direct contact with a first side of cathode gas diffusion layer 13.

In accordance with an embodiment of the present invention, the configuration of the apparatus permits water comprised in the cathode gas diffusion layer 13 to flow in an in-plane direction in the cathode gas diffusion layer 13.

In accordance with an embodiment of the present invention, within the at least one anode catalyst layer 16 occurs a water oxidation reaction occurs, and within the at least one cathode catalyst layer 14 an oxygen reduction reaction occurs.

The surface of the gas diffusion layer 13 (or additional gas diffusion layer 20) adjacent to gas transport layer 3 is covered at least in proportion of 10% with the gas transport layer 3, preferably at least 70% and even more preferably at least 95%.

In accordance with an embodiment of the present invention, a porosity of the electrically conductive porous gas transport layer 3 is between about 0.1 micrometers and 100 micrometers.

In accordance with an embodiment of the present invention, a pressure drop induced by the electrically conductive porous gas transport layer 3 between a gas cavity from which the oxygen-containing gas is sourced and the cathode gas diffusion layer 13 is of at least 1 mbar, preferably at least 20 mbar and even more preferably 100 mbar.

In accordance with an embodiment of the present invention, the electrically conductive porous gas transport layer 3 comprises one of porous transition metals, post-transition metals, carbon comprising materials or a combination thereof.

In accordance with an embodiment of the present invention, the current density at the membrane electrode assembly 4 is between about 30 mA/cm2 and 900 mA/cm2.

In accordance with an embodiment of the present invention, a voltage applied between the at least one cathode catalyst layer 14 and the at least one anode catalyst layer 16 is between about 1.2 and about 3.5 V.

Although a plurality of features characteristic for the various embodiments of the present invention have already been discussed in detail above, in the following these and others will be discussed in connection with embodiments of the present invention illustrated in the appended drawings.

FIG. 1 is a schematic representation a portion of the apparatus of the present invention, exhibiting an electrically conductive porous gas transport layer, along with components of a membrane-electrode assembly, in accordance with an embodiment of the present invention.

The apparatus of FIG. 1 comprises the electrically conductive porous gas transport with the membrane-electrode assembly, while with numeral 3 is indicated the electrically conductive porous gas transport layer, with numeral 13 is indicated the cathode gas diffusion layer, with numeral 14 is indicated the cathode catalyst layer, with numeral 15 is indicated the polymer exchange membrane, with numeral 16 is indicated the anode catalyst layer and with numeral 17 is indicated the anode current collector.

The electrically conductive porous gas transport layer delivers gas to the cathode gas diffusion layer, while at the same time serving as the cathode current collector. The cathode gas diffusion layer has a water flow in the in-plane direction, as indicated by the arrow, and gas bubbles from the electrically conductive porous gas transport layer navigate through the water to reach the cathode catalyst layer. The cathode catalyst layer reduces oxygen to hydrogen peroxide, which rapidly exits the catalyst layer and dissolves in the water flowing through the cathode gas diffusion layer. The anode catalyst layer oxidizes water into protons, which cross the polymer exchange membrane to reach the cathode catalyst layer. The anode current collector provides electrical signal to the anode catalyst layer.

FIG. 2 is a schematic view of a design for an electrochemical cell, in accordance with another embodiment of the present invention.

The apparatus of FIG. 2 comprises an electrochemical cell, while with numeral 1 is indicated the electrochemical cell, with numeral 2 is indicated the cathode plate, with numeral 3 is indicated the electrically conductive porous gas transport layer, with numeral 4 is indicated the membrane electrode assembly, with numeral 5 is indicated the anode chamber, with numeral 6 is indicated the gas inlet, with numeral 7 is indicated the cathode water inlet, with numeral 8 is indicated the cathode water, oxygen and peroxide outlet, with numeral 9 is indicated the anode input and with numeral 10 is indicated the anode output.

Oxygen-containing gas is introduced through the gas inlet, and goes through the electrically conductive porous gas transport layer to be dispersed homogeneously over the cathode side of the membrane electrode assembly. Water is inserted through the cathode water inlet, and flows in the in-plane direction of the cathode gas diffusion layer. Excess gas, water and hydrogen peroxide exit through the cathode outlet. Water is also inserted through the anode input to enter the anode chamber, where it is oxidized to oxygen, and excess water exits through the anode output. A voltage difference is applied between the anode and cathode sides of the membrane electrode assembly.

FIG. 3 is a further schematic view of a configuration for an electrochemical cell design, in accordance with yet another embodiment of the present invention.

The apparatus of FIG. 3 comprises an electrochemical cell, while with numeral 1 is indicated the electrochemical cell, with numeral 2 is indicated the cathode plate, with numeral 3 is indicated the electrically conductive porous gas transport layer, with numeral 4 is indicated the membrane electrode assembly, with numeral 5 is indicated the anode chamber, with numeral 6 is indicated the gas inlet, with numeral 9 is indicated the anode water inlet and with numeral 10 is indicated the anode water outlet. In distinction from the configuration represented in FIGS. 1 and 2, the configuration represented in FIG. 3 the cathode water inlet 11 and the cathode outlet 12 are placed through the electrically conductive porous gas transport layer, as indicated by the dotted lines. Oxygen-containing gas is introduced through the gas inlet, and is directed through dedicated openings towards the electrically conductive porous gas transport layer to be dispersed homogeneously over the cathode side of the membrane electrode assembly. Water is inserted through the cathode water inlet, passes through dedicated paths through the cathode plate and the electrically conductive porous gas transport layer and flows in the in-plane direction of the cathode gas diffusion layer. Excess gas, water and hydrogen peroxide exit through the cathode outlet. Water is also inserted through the anode input to enter the anode chamber, where it is oxidized to oxygen, and excess water exits through the anode output. A voltage difference is applied between the anode and cathode sides of the membrane electrode assembly.

FIG. 4 is an exploded view of the electrochemical cell design of FIG. 1.

The apparatus of FIG. 4 comprises an electrochemical cell, while with numeral 1 is indicated the electrochemical cell, with numeral 2 is indicated the cathode plate, with numeral 3 is indicated the electrically conductive porous gas transport layer, with numeral 4 is indicated the membrane electrode assembly, with numeral 5 is indicated the anode chamber, with numeral 18 is indicated the cathode end plate, with numeral 19 is indicated the cathode current collector, with numeral 20 is indicated one or more additional cathode gas diffusion layers, with numeral 21 is indicated the anode gasket and with numeral 22 is indicated the anode end plate. It has been found, that one or even more additional cathode gas diffusion layers significantly improves the performance of the cell.

FIG. 5 is a flow diagram of the method comprised in the present application, while with numeral 1 is indicated the electrochemical cell, with numeral 23 the cathode pump, controlling the water flow to the cathode, with numeral 24 the gas pump, oxygen concentrator or air compressor delivering gas to the electrochemical cell, with numeral 25 the cathode outlet containing water, gas and hydrogen peroxide, with numeral 26 the anode pump, with numeral 27 the anode outlet, with numeral 28 the power supply and with numeral 29 the hydrogen peroxide sensor. The hydrogen peroxide sensor measures concentration at the outlet, which is used to automatically regulate the flow delivered by the cathode pump 23 and the current at the power supply in keeping a constant concentration.

In the following an example embodiment for the method of making the apparatus of the present invention will be discussed.

The anode of the electrochemical cell 1 is prepared by depositing Iridium oxide nanoparticles on a cation polymer exchange membrane. The thickness of the polymer exchange membrane is 135 μm, but thicker or thinner membranes may also be used without affecting the resulting abilities of the electrochemical cell. Preferably, the membrane is between 5 and 500 μm in thickness and more preferably between 20 and 200 μm. A current collector is placed on the anode side of the membrane in direct contact with the iridium oxide nanoparticles. The material of the current collector is selected to withstand oxidizing conditions and is preferably Titanium and/or its oxides, tantalum and/or its oxides, gold, carbon, stainless steel or platinum, among others. The current collector material may also be an electrically conducting material, coated with platinum, iridium and its oxides, titanium and its oxides or tantalum and its oxides. The purpose of this coating is to obtain suitable electrical contact to the anode catalyst, which could be facilitated by the application of pressure and/or temperature during the cell fabrication process. In this example, a Titanium felt was used as an anode current collector.

The cathodes were obtained by coating a gas diffusion layer with a suitable catalyst material. Gas diffusion layers could be hydrophilic or hydrophobic and contain coatings of PTFE or other substances in order to control the hydrophobicity. Coating was done by dispersing suitable catalyst nanoparticles in ethanol, water and ionomer to form a catalyst ink, which can then be sprayed or deposited by other means onto the gas diffusion layer. Suitable cathode catalysts should be selective towards oxygen reduction to hydrogen peroxide, and include Pt—Hg, Pd—Hg, Cu—Hg, Ag—Hg, Ag, Au, carbon, graphene, nitrogen doped carbon, Sulphur doped carbon, Cobalt porphyrins and phthalocyanines, transition metal sulfides and nitrides and any combinations thereof.

The anode current collector, and the membrane together with the anode catalyst layer coated on one side of the membrane and the cathode placed on the other side, were assembled and heat pressed for 5 minutes at 130 degrees Celsius, under a pressure of 200 kg/cm2. This resulted in a membrane electrode assembly, which is a single mechanical entity.

Following this assembly step, the membrane electrode assembly was placed in a suitable cell housing, as shown in FIG. 2. The cell housing consists of an anode chamber, where the anode side of the cell is placed, an electrically conductive porous gas transport layer, where the cathode side of the cell is placed, and a cathode housing that provides mechanical support for the electrically conductive porous gas transport layer. During assembly it was established to be very important that the electrically conductive porous gas transport layer is flat, and that it homogeneously contacts the cathode gas diffusion layer. This is very important as any deviations would facilitate water escaping from the desired path in-plane of the cathode gas diffusion layer, and taking a path outside of it as it offers less resistance and pressure drop. This would result in a lower efficiency in the removal of hydrogen peroxide from the cathode catalyst layer, and overall lower performance of the electrochemical cell.

In the following a method for making hydrogen peroxide will be discussed, while employing the apparatus of the present invention.

An apparatus in accordance with the present invention produces hydrogen peroxide based on the following half-cell reactions:


2H2O→O2+4H++4e−  Anode:


2O2+4H++4e−→2H2O2  Cathode:

While producing hydrogen peroxide, it is also important to minimize hydrogen peroxide decomposition, which can take place chemically:


2H2O2→2H2O+O2

Or electrochemically:


H2O2+2H++2e−→2H2O

Other proton sources could be used at the anode without affecting the nature of the invention; these include ethanol, methanol, hydrogen and others, which will be apparent to those versed in the art.

Exemplarily, the cathode side of the cell is fed with a gas flow of 22 ml/min/cm2, normalized to electrode area, with a preferred range of 0.01 to 100 mL/min/cm2. The pressure at the cathode is set between 0.01 and 10 bar. The anode was fed a water flow at 0.3 ml/min/cm2, normalized to electrode area and can be varied in the range of 0.01 to 50 ml/min/cm2. Water was also fed in between the cathode electrode and the ion exchange membrane in a suitable flow to produce a hydrogen peroxide concentration of 1000 to 3000 mg/L, and preferably the concentration can be set between 200 mg/L to 50000 mg/L, even more preferably between 5000 to 30000 mg/L. The current density was set to 100 mA/cm2 but can preferably be set in the range of 10 to 500 mA/cm2. The potential corresponding to the 100 mA/cm2 was measured to 1.9 V.

The embodiments and examples described above are intended to be merely illustrative and non-limiting. Those skilled in the art will recognize or will be able to ascertain, using no more than routine experimentation, numerous equivalents of specific compounds, materials, devices, and procedures. All such equivalents are considered to be within the scope and are encompassed by the appended claims.

The language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the disclosure be limited not by this detailed description, but rather by any claims that issue on an application based hereon. Accordingly, the disclosure of the embodiments is intended to be illustrative, but not limiting, of the scope of the disclosure, which is set forth in the following claims.

Claims

1. An apparatus for producing hydrogen peroxide, comprising one or more neighboring electrochemical cells (1),

each electrochemical cell (1) comprising:
a membrane electrode assembly (4) comprising at least one cathode gas diffusion layer (13), at least one cathode catalyst layer (14), at least one ion exchange membrane (15), at least one anode catalyst layer (16), at least one anode current collector (17) and a cathode water inlet connected to a cathode pump (23) for the delivery of water,
wherein in said membrane electrode assembly (4) a first side of the ion exchange membrane (15) being bound against a second side of said cathode catalyst layer (14) and said anode catalyst layer (16) being bound against an opposing second side of the ion exchange membrane (15), and
at least one electrically conductive porous gas transport layer (3) having a hydrophobic surface, being flat and homogenously contacting the cathode gas diffusion laver (13) on a first side, said gas transport layer (3) being configured to deliver a flow of oxygen-containing gas in a through plane direction towards the cathode gas diffusion layer (13) said gas diffusion layer having a pore size larger than the electrically conductive porous gas transport layer to facilitate water flow through it and the gas transport laver further being configured to collect current and the cathode gas diffusion layer further comprising water which is configured to flow through the porous gas transport layer 3 in an in plane direction; and
wherein said gas diffusion layer (13) is suitable to transport oxygen, water and hydrogen peroxide to/from the cathode catalyst layer (14).

2. The apparatus of claim 1, comprising at least one additional gas diffusion layer (20) situated between the gas transport layer (3) and the cathode gas diffusion layer (13).

3. The apparatus of claim 1,

wherein within said at least one anode catalyst layer (16) a water oxidation reaction is configured to occur, and
wherein within said at least one cathode catalyst layer (14) an oxygen reduction reaction is configured to occur.

4. The apparatus of claim 2,

wherein a surface of the gas diffusion layer 13 (or additional gas diffusion layer 20) adjacent to the gas transport layer 3 is covered at least in proportion of 10% with the gas transport layer 3, preferably at least 70% and even more preferably at least 95%.

5. The apparatus of claim 1,

wherein a porosity of said electrically conductive porous gas transport layer (3) is between about 0.1 micrometers and 100 micrometers and a thickness between 0.5 and 10 mm.

6. The apparatus of claim 1,

wherein a pressure drop induced by the electrically conductive porous gas transport layer (3) between a gas cavity from which said oxygen-containing gas is sourced and said cathode gas diffusion layer (13) is of at least 1 mbar.

7. The apparatus of claim 1,

wherein said electrically conductive porous gas transport layer (3) comprises one of: porous transition metals, post-transition metals, carbon comprising materials or a combination thereof.

8. The apparatus of claim 1,

wherein current density at the membrane electrode assembly (4) is between about 30 mA/cm2 and 900 mA/cm2.

9. The apparatus of claim 1,

wherein a voltage applied between the at least one cathode catalyst layer (14) and the at least one anode catalyst layer (16) is between about 1.2V and about 3.5V.

10. A system, comprising:

an apparatus in accordance with claim 1, and
a device facilitating the combination of hydrogen peroxide generated by said apparatus and ultra-violet light or ozone to facilitate the formation of hydroxyl radicals.

11. (canceled)

12. A method of producing hydrogen peroxide, using the apparatus of claim 1

said gas transport layer (3) delivering a flow of oxygen-containing gas in a through plane direction toward the cathode gas diffusion layer (13) and collecting current wherein water is flowing through the porous gas transport layer (3) in an in-plane direction, and
wherein hydrogen peroxide is generated at the cathode catalyst layer (14) and is dissolved in the flowing water, and wherein the hydrogen peroxide is pushed out of the cathode catalyst layer (14).

13. A method according to claim 12, whereby the hydrogen peroxide concentration is measured and is used to automatically regulate the flow of water delivered by a cathode pump 23 and the current at the power supply in keeping a constant concentration.

Patent History
Publication number: 20240060195
Type: Application
Filed: Aug 17, 2022
Publication Date: Feb 22, 2024
Inventors: Rajath Sathyadev Rajmohan (Rødovre), Rasmus Frydendal (Brønshøj), Arnau Verdaguer Casadevall (København NV), Ziv Gottesfeld (Tel Aviv)
Application Number: 17/889,599
Classifications
International Classification: C25B 1/30 (20060101); C25B 13/00 (20060101); C25B 11/032 (20060101); C25B 9/19 (20060101); C25B 11/091 (20060101); C25B 11/063 (20060101);