BIFUNCTIONAL WATER SPLITTING CATALYSTS AND ASSOCIATED METHODS
A catalyst, including a conductive substrate coated with a metal-phosphorus-derived film, where the metal is Manganese, Iron, Cobalt, Nickel, or Copper. In some embodiments, the conductive substrate includes copper, titanium, glassy carbon, fluorine-doped tin oxide, indium-doped tin oxide, tin, nickel, or stainless steel. Methods for producing the catalysts and for hydrogen evolution reactions and oxygen evolution reactions employing the catalysts are also described herein.
This application claims priority to U.S. Provisional Patent Application No. 62/141,081, filed on Mar. 31, 2015, the entirety of which is incorporated by reference.
TECHNICAL FIELDThe present disclosure relates to catalysts and methods for hydrogen and/or oxygen evolution from water. More specifically, it relates to metal-phosphorus-derived film catalysts and methods and applications of the same.
BACKGROUNDElectrocatalytic water splitting, which consists of H2 evolution reactions (“HER”) and O2 evolution reactions (“OER”) has attracted increasing interest in the last few years because of its critical importance in the context of renewable energy research. Most efforts in this field are devoted to developing HER catalysts under strongly acidic conditions for proton-exchange membrane electrolyzers, whereas OER catalysts operate under strongly basic conditions for alkaline electrolyzers. Transition-metal chalcogenides, pnictides, carbides, borides, and even metal-free materials have been reported for HER catalysis in strongly acidic electrolytes. On the other hand, many innovative noble-metal-free OER catalysts based on the oxides/hydroxides of cobalt, nickel, manganese, iron, and copper have also been reported with mediocre to excellent OER catalytic activities under basic conditions.
Despite these advances, challenges for large-scale water splitting catalysis still exist. For instance, to accomplish overall water splitting, it is necessary to integrate both HER and OER catalysts in the same electrolyte. Unfortunately, the current prevailing approaches often lead to inferior overall performance because of the incompatibility of the two types of catalysts functioning under the same conditions. Therefore, it is highly desirable to develop bifunctional and low-cost electrocatalysts that are simultaneously active for both HER and OER in the same electrolyte. Also, ionic conductivity is usually higher at extreme pH values than under neutral conditions and the overpotential loss of OER is much larger than that of HER, plus most OER catalysts are vulnerable in strongly acidic media.
SUMMARYThe present disclosure in aspects and embodiments addresses these various needs and problems by providing a catalyst, comprising a conductive substrate coated with a metal-phosphorus-derived film, wherein the metal is selected from the group consisting of Manganese, Iron, Cobalt, Nickel, and Copper. In some embodiments, the conductive substrate comprises a material selected from the group consisting of copper, titanium, glassy carbon, fluorine-doped tin oxide, indium-doped tin oxide, tin, nickel, and stainless steel.
Methods for producing the catalysts and for HER and OER are also disclosed herein.
The drawings below are supplied in order to facilitate understanding of the Description and Examples provided herein.
The present disclosure covers apparatuses and associated methods for the production and related applications of metal-phosphorous-derived films as hydrogen evolution catalysts. In the following description, numerous specific details are provided for a thorough understanding of specific preferred embodiments. However, those skilled in the art will recognize that embodiments can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In some cases, well-known structures, materials, or operations are not shown or described in detail in order to avoid obscuring aspects of the preferred embodiments. Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in a variety of alternative embodiments. Thus, the following more detailed description of the embodiments of the present invention, as illustrated in some aspects in the drawings, is not intended to limit the scope of the invention, but is merely representative of the various embodiments of the invention.
In this specification and the claims that follow, singular forms such as “a,” “an,” and “the” include plural forms unless the content clearly dictates otherwise. All ranges disclosed herein include, unless specifically indicated, all endpoints and intermediate values. In addition, “optional” or “optionally” refer, for example, to instances in which subsequently described circumstance may or may not occur, and include instances in which the circumstance occurs and instances in which the circumstance does not occur. The terms “one or more” and “at least one” refer, for example, to instances in which one of the subsequently described circumstances occurs, and to instances in which more than one of the subsequently described circumstances occurs.
The present disclosure covers methods, compositions, reagents, and kits for metal-phosphorus-derived films as competent hydrogen evolution catalysts or oxygen evolution catalysts.
Aspects of the present disclosure may be further described in Jian, N., You, B, Sheng, M, and Sun, Y., Bifunctionality and Mechanism of Electrodepoited Nickel-Phosphorus Films for Efficient Overall Water Splitting, 8 ChemCatChem 1-6-112 (Dec. 4, 2015) and in Jian, N., You, B, Sheng, M, and Sun, Y., Electrodeposited Cobalt-Phosphorus-Derived Films as Competent Bifunctional Catalysts for Overall Water Splitting, 54 Angew, Chem. Int. Ed. 6251-6254 (Apr. 20, 2015). The entirety of these papers are incorporated herein by reference.
In embodiments, the catalysts include a conductive substrate coated with a metal-phosphorus-derived film.
Conductive Substrates:
Any suitable conductive material capable of being coated with a metal-phosphorus-derived film may be employed in the catalyst. Exemplary conductive substrates include: copper, titanium, glassy carbon, fluorine-doped tin oxide, indium-doped tin oxide, nickel, tin, and stainless steel. Metal foils, such as copper foil may be employed in embodiments where the conductive substrate is a metal.
Metal-Phosphorus-Derived Film:
The metal-phosphorus-derived films may use any suitable metal source. Exemplary metals that may be employed in the metal-phosphorus-derived films include: manganese, iron, cobalt, nickel, and copper. In some embodiments, combinations of more than one metal may be used to produce the metal-phosphorus-derived film.
The metal-phosphorus-derived films may be configured to have a suitable concentration of phosphorus. Exemplary phosphorus/metal ratios include from about 1/20 to about 1/1. In embodiments, phosphorus may be present in the metal-phosphorus-derived films in concentrations, by atomic percentage, of greater than 0 to about 50%, from about 5% to about 50%, from about 5% to about 20%, and about 10%. The ratio of phosphorus to metal may be adjusted depending on the metal being used. For example, in some embodiments employing cobalt as the metal, phosphorous may be present, by atomic percentage, in concentrations of about 5% to about 15%, from about 7% to about 12%, or about 10%. In embodiments employing nickel as the metal, phosphorous may be present, by atomic percentage, in concentrations of about 25% to about 35%, from about 27% to about 32%, or about 30%.
Any suitable metal source may be employed. In embodiments, affordable metal sources are preferred. Metal chlorides, nitrates, and sulfates salts may be used. For cobalt-phosphorus-derived films, exemplary cobalt sources include cobalt chloride, cobalt sulfate, and cobalt nitrate. For nickel-phosphorus-derived films, exemplary nickel sources include nickel chloride, nickel sulfate, and nickel nitrate. For manganese, iron, and copper-phosphorous-derived films, exemplary metal sources include metal-chlorides, sulfates, and nitrates.
Any suitable phosphorus source may be used. In embodiments, exemplary phosphorus sources include NaH2PO2.
Production Methods:
Catalysts described in this application may be produced by electrodeposition of the metal-phosphorus-derived film on the conductive substrate. Potentiodynamic deposition methods may be employed to produce catalysts. For example, a NiP film may be readily prepared by potentiodynamic deposition from NiCl2 and NaH2PO2 in the presence of glycine. In such an embodiment, glycine plays an important role in controlling the deposition potential and rate of the Ni—P film.
Exemplary films may reach current densities of 10 mAcm−2 with overpotentials of −93 to −94 mV for HER and 344 to 345 mC for OER with very small Tefel slopes of 42 to 43 and 47 to 49 mV dec−1, for HER and OER respectively.
Electrolysis Solutions:
Any suitable electrolysis solution may be used for the production of hydrogen or oxygen. Suitable electrolysis solutions include aqueous solutions comprising a conductive electrolyte. In some embodiments, an alkaline electrolyte or combination thereof, such as KOH or NaOH, may be used in about 1.0 M concentrations. In some embodiments, the electrolysis solution has a pH of from about 7 to about 14, or about 14.
EXAMPLESThe following examples are illustrative only and are not intended to limit the disclosure in any way.
Example 1 Cobalt-Phosphorous-Derived FilmsAs described in detail below, cobalt-phosphorous-derived (“Co—P”) films were deposited onto a copper foil substrate using a facile potentiodynamic electrodeposition with cobalt and phosphorous reagents. The as-prepared Co—P films can be directly utilized as electrocatalysts for both HER and OER in strong alkaline electrolyte, which can achieve a current density of 10 mA/cm2 with overpotentials of −94 mV for HER and 345 mV for OER with very small Tafel slopes, 45 and 47 mV/dec, respectively. When the Co—P films were deposited on an anode and cathode for overall water splitting, the superior activity and stability of the catalytic films can even compete versus the integrated Pt and IrO2 catalyst couple.
Materials
Cobalt sulfate, sodium acetate, sodium hypophosphite monohydrate, potassium hydroxide were purchased from commercial vendors and used as received. Pt—C (20% Pt on Vulcan XC-72) and iridium (IV) oxide were purchased from Premeteck Co. and Alfa Aesa, respectively, and used as received. Nafion 117 solution (5% in a mixture of lower aliphatic alcohols and water) was purchased from Sigma-Aldrich. Copper foils (3M™ copper conductive tapes, single adhesive surface) were purchased from Ted Pella, Inc. Water was deionized (18Ω) with a Barnstead E-Pure system.
Electrochemical Methods
Electrochemical experiments were performed on Gamry Interface 1000 potentiostats. Aqueous Ag/AgCl reference electrodes (saturated KCl) were purchased from CH Instruments. The reference electrode in aqueous media was calibrated with ferrocenecarboxylic acid whose Fe3+/2+ couple is 0.284 V vs SCE. All potentials reported in this paper were converted from vs Ag/AgCl to vs RHE by adding a value of 0.197+0.059×pH to vs RHE. iR (current times internal resistance) compensation was applied in polarization and controlled potential electrolysis experiments to account for the voltage drop between the reference and working electrodes using the Gamary Framework™ Data Acquisition Software 6.11.
Preparation of Co—P Films
Prior to electrodeposition, copper foils were rinsed with water and ethanol thoroughly to remove residual organic species. For linear sweep voltammetry experiments, a circular copper foil with a 3 mm diameter was prepared and pasted on the rotating disk glassy carbon electrode, then the assembled electrode was exposed to the deposition solution (50 mM CoSO4, 0.5 M NaH2PO2, and 0.1 M NaOAc in water). A platinum wire was used as the counter electrode and a Ag/AgCl (sat. KCl) electrode as the reference electrode. Nitrogen was bubbled through the electrolyte solution for at least 20 min prior to deposition and maintained during the entire deposition process. The potential of consecutive linear scans was cycled 15 times between −0.3 and −1.0 V vs Ag/AgCl at a scan rate of 5 mV/s under stirring and a rotation rate of 500 rpm. After deposition, the assembled electrode was removed from the deposition bath and rinsed with copious water gently. The prepared Co—P film can be directly used to collect its polarization curves or stored under vacuum at room temperature for future use. For samples prepared for controlled potential electrolysis, a copper foil was directly used the working electrode with a geometric area of 0.3 cm2 exposed to the electrolyte. The deposition potential window and cycle number are the same as aforementioned. Typical potentiodynamic depositions of Co—P films are shown in
Preparation of Pt—C and IrO2-Loaded Electrodes
12 mg Pt—C or IrO2 were dispersed in a 2 mL mixture solution containing 800 μL water, 120 μL 5% Nafion solution, and 1.08 mL ethanol, followed by sonication for 30 min to obtain a homogeneous catalyst ink. 2 μL catalyst ink was loaded on the surface of a glassy carbon electrode (surface area: 0.07065 cm2) for 6 times. Consequently, the overall loading amount is 1 mg/cm2.
Physical Methods
Scanning electron microscopy images and elemental mapping analysis were collected on a FEI QUANTA FEG 650 (FEI, USA) by FenAnn Shen at the Microscopy Core Facility of USU. Cobalt and phosphorous analysis were obtained on a Thermo Electron iCAP inductively coupled plasma spectrophotometer at the Analytical Laboratory of USU. X-ray photoelectron spectroscopy analyses were done using a Kratos Axis Ultra instrument (Chestnut Ridge, N.Y.) at Surface Analysis and Nanoscale Imaging group at the University of Utah, sponsored by the College of Engineering, Health Sciences Center, Office of the Vice President for Research, and the Utah Science Technology and Research (USTAR) Initiative of the State of Utah. The samples were affixed on a stainless steel Kratos sample bar, loaded into the instrument's load lock chamber, and evacuated to 5×10−8 torr before it was transferred into the sample analysis chamber under ultrahigh vacuum conditions (˜10−10 torr). X-ray photoelectron spectra were taken using the monochromatic Al Kα source (1486.7 eV) at a 300×700 μm spot size. Low resolution survey and high resolution region scans at the binding energy of interest were taken for each sample. To minimize charging, samples were flooded with low-energy electrons and ions from the instrument's built-in charge neutralizer. The samples were also sputter cleaned inside the analysis chamber with 1 keV Ar+ ions for 30 seconds to remove adventitious contaminants and surface oxides. Data were analyzed using CASA XPS software, and energy corrections on high resolution scans were done by referencing the C1s peak of adventitious carbon to 284.5 eV. This work also made use of the Surface Analysis and Nanoscale Imaging group at the University of Utah. The generated hydrogen volume during electrolysis was quantified with a SRI gas chromatography system 8610C equipped with a Molecular Sieve 13× packed column, a HayesSep D packed column, and a thermal conductivity detector. The oven temperature was maintained at 60° C. and argon was used as the carrier gas.
Results
Cobalt-phosphorous-derived (“Co—P”) films were deposited onto a copper foil substrate using a facile potentiodynamic electrodeposition with cobalt and phosphorous reagents.
We first evaluated the HER activity of a Co—P film in strong alkaline solution (See
Remarkably, the Co—P film was able to produce a catalytic current density of 1000 mA/cm2 within an overpotential of −227 mV. The linear fitting of its Tafel plot (
To probe the morphology and composition of the Co—P film after HER electrocatalysis, the SEM and XPS results of a post-HER Co—P film were collected. As shown in
We next assessed the catalytic activity of the Co—P film for OER in the same electrolyte (See
Linear fitting of its Tafel plot resulted in a Tafel slope of 47 mV/dec (
The SEM image of the post-OER Co—P film (
Based on the results aforementioned, we anticipated that the Co—P film could act as a bifunctional electrocatalyst for overall water splitting. Hence, a two-electrode configuration was employed, with Co—P and on Cu substrates were used as both the anode and the cathode (i.e., Co—P/Co—P). The performance of the Co—P/Co—P configurations were compared to the performance of IrO2/Pt—C, Pt—C/Pt—C, and IrO2/IrO2 configurations (see
The rapid catalytic current density exceeded 100 mA/cm2 at 1.744 V. When Pt—C or IrO2 was used for both electrodes (Pt—C/Pt—C or IrO2/IrO2 couple), much diminished catalytic current densities were obtained with large Tafel slopes of 166 and 290 mV/dec, respectively. Since Pt is well-known for HER and IrO2 for OER, the integration of Pt—C on cathode and IrO2 on anode was expected to produce an excellent catalytic system. Indeed, the IrO2/Pt—C couple was able to catalyze water splitting with an onset around 1.47 V (
In conclusion, we have reported electrodeposited Co—P films can act as bifunctional catalysts for overall water splitting. The catalytic activity of the Co—P films can rival the state-of-the-art catalysts, requiring η=−94 mV for HER and η=345 mV for OER to reach 10 mA/cm2 with Tafel slopes of 45 and 47 mV/dec, respectively. It can be directly utilized as catalysts for both anode and cathode with superior efficiency, strong robustness, and 100% Faradaic yield. The understanding of real-time composition and structural evolution of the film during electrolysis requires in situ spectroscopic study, which is under current investigation.
Example 2 Nickel-Phosphorous-Derived FilmsAs described in detail below, nickel-phosphorous-derived (“Ni—P”) films were deposited onto a copper foil substrate using a facile potentiodynamic electrodeposition with cobalt and phosphorous reagents. The as-prepared Ni—P films can be directly utilized as electrocatalysts for both HER and OER in strong alkaline electrolyte, (1.0 M KOH).
Materials
Nickel chloride hexahydrate (NiCl2.6H2O), glycine, sodium hypophosphite monohydrate (NaH2PO2—H2O), sodium acetate (NaOAc), and potassium hydroxide (KOH) were all purchased from commercial vendors and used directly without any further purification. Nafion 117 solution (5% in a mixture of lower aliphatic alcohols and water) was purchased from Sigma-Aldrich. Copper foils (3M™ copper conductive tapes, single adhesive surface) were purchased from Ted Pella, Inc. Water was deionized (18 MQ) using a Barnstead E-Pure system.
Preparation of Catalyst Films (Ni—P and NiOx)
Prior to electrodeposition, copper foils were rinsed with water and ethanol thoroughly to remove residual organic species. For linear sweep voltammetry experiments, a circular copper foil with a 3 mm diameter was prepared and pasted on the rotating disk glassy carbon electrode, and then the assembled electrode was exposed to the optimized deposition solution (50 mM NiCl2, 1 M NaH2PO2, 0.16 M glycine, and 0.1 M NaOAc in water). A platinum wire was used as the counter electrode and a Ag/AgCl (sat. KCl) electrode as the reference electrode. Nitrogen was bubbled through the electrolyte solution for at least 20 min prior to deposition and maintained during the entire deposition process. The potential of consecutive linear scans was cycled between 0.1 and −1.1 V vs Ag/AgCl at a scan rate of 5 mV/s and a rotation rate of 500 rpm (
The HER and OER polarization curves of Ni—P films prepared via potentiodynamic deposition cycles of 5, 10, 15, and 20 are compared in
The control NiOx catalyst films were prepared according to a reported method (J. Phy. Chem. C 2014, 118, 4578-4584, the complete disclosure of which is herein incorporated by reference in its entirety). Briefly, a copper foil with an exposed area of 0.3 cm2 was used as the working electrode with platinum wire and Ag/AgCl (sat. KCl) as the counter and reference electrodes, respectively. 10 mL 0.1 M NaBi with 1.0 mM Ni(NO3)2 was used as the electrolyte. Prior to electrodeposition, the copper foil was rinsed with acetone and deionized water thoroughly. Electrolysis was carried out at −1.2 V vs Ag/AgCl for three hours under deaerated condition.
Preparation of Pt—C and IrO2-Loaded Electrodes
12 mg Pt—C or IrO2 was dispersed in a 2 mL mixture solution containing 800 μL water, 120 μL 5% Nafion solution, and 1.08 mL ethanol, followed by sonication for 30 min to obtain a homogeneous catalyst ink. 3 μL catalyst ink was loaded on the surface of a glassy carbon electrode (surface area: 0.07065 cm2) for 6 times. Consequently, the overall loading amount is 1.53 mg/cm2.
Catalyst Characterization
Powder X-ray diffractions were recorded on a Rigaku MiniflexII Desktop X-ray diffractometer. Scanning electron microscopy (SEM) images were collected on a FEI QUANTA FEG 650 (FEI, USA). Elemental analysis of nickel and sulfur was obtained on a Thermo Electron iCAP inductively coupled plasma spectrophotometer. Fourier transform infrared (FTIR) spectroscopy was conducted on an IR100 Spectrometer (Thermo Nicolet). The Raman spectra were recorded with a confocal Raman microspectrometer (Renishaw, U.K.) under a 785 nm diode laser excitation. The detection of the Raman signal was carried out with a Peltier cooled charge-coupled device (CCD) camera. The software package WIRE 3.0 (Renishaw) was employed for spectral acquisition and analysis. X-ray photoelectron spectroscopy analyses were conducted on a Kratos Axis Ultra instrument (Chestnut Ridge, N.Y.). The samples were affixed on a stainless steel Kratos sample bar, loaded into the instrument's load lock chamber, and evacuated to 5×10−8 torr before it was transferred into the sample analysis chamber under ultrahigh vacuum conditions (˜10−10 torr). X-ray photoelectron spectra were taken using the monochromatic Al Kα source (1486.7 eV) at a 300×700 μm spot size. High resolution region scans at the binding energies of interest were taken for each sample. To minimize charging, samples were flooded with low-energy electrons and ions from the instrument's built-in charge neutralizer. The samples were first sputter cleaned inside the analysis chamber with 1 keV Ar+ ions for 30 seconds to remove adventitious contaminants and surface oxides. Data were analyzed using CasaXPS software, and energy corrections on high resolution scans were calibrated by referencing the C1s peak of adventitious carbon to 284.5 eV.
Electrochemical Measurements
Electrochemical experiments were performed on a Gamry Interface 1000 potentiostat workstation with a three-electrode cell system. The as-prepared Ni—P (d=3 mm, S=0.07065 cm2) was used as the working electrode, a Ag/AgCl (sat. KCl) electrode (CH Instruments) as the reference electrode, and a platinum wire as the counter electrode. All potentials reported in the paper were converted to vs RHE (reversible hydrogen electrode) by adding a value of 0.197+0.059×pH to vs RHE. iR (current times internal resistance) correction was applied for linear sweep voltammetry and controlled potential electrolysis experiments to account for the voltage drop between the reference and working electrodes using Gamry Framework™ Data Acquisition Software 6.11. The linear sweep voltammetry experiments were conducted in N2 saturated 1.0 M KOH electrolyte at a scan rate of 2 mV/s and a rotating speed of 2000 rpm. Electric impedance spectroscopy measurements in deaerated 1.0 M KOH were carried out in the same configuration at multiple potentials from 105 to 0.1 Hz with an AC potential amplitude of 30 mV.
Results
The Ni—P film can be readily prepared via potentiodynamic deposition from NiCl2 and NaH2PO2 in the presence of glycine (
The scanning electron microscopy (SEM) image of an as-prepared Ni—P film is shown in
The electrocatalytic activity of Ni—P was first evaluated for H2 evolution in a strongly alkaline electrolyte (1.0 M KOH), as shown in
Even more remarkably, the Ni—P film was able to produce a catalytic current density of 500 mA/cm2 within an overpotential of −219 mV. The derived Tafel plot (
We next collected the SEM and XPS results of a post-HER Ni—P sample to determine possible morphology and composition change after a 2-h HER electrocatalysis at −110 mV vs RHE when stable catalytic current was achieved (
The OER electrocatalytic performance of Ni—P was next assessed in the same electrolyte, 1.0 M KOH.
The quick surpass of Ni—P over IrO2 in OER activity was well rationalized by their different Tafel slopes. As shown in
The SEM image of a Ni—P film after a 2-h OER electrolysis at η=350 mV in 1.0 M KOH is shown in
Given the aforementioned results, we concluded that the Ni—P film was partially oxidized to nickel oxides/hydroxides during OER (most likely on the film surface), while the bulk composition of the post-OER film still retained as the original Ni—P. It should be noted that core-shell structure has been reported for Ni2P nanowires as OER electrocatalysts, wherein the shell was mainly composed of nickel oxides/hydroxides while the core remained as Ni2P. Elemental analysis of the post-OER film resulted in the remaining amounts of nickel and phosphorous as 1.24 and 0.29 mg/cm2 with a Ni/P atomic ratio of 2.25. It is interesting to note that the control sample NiOx which might also possess a metallic nickel core and a nickel oxide shell was unable to compete with our Ni—P in terms of both HER and OER activities, which undoubtedly prove the beneficial role that phosphorous plays in water splitting electrocatalysis.
Since the polarization-derived Tafel slopes aforementioned might overlook the impact of electron transport in the catalyst material on HER and OER performance, we further carried out detailed electrochemical impedance spectroscopy (EIS) studies to probe the intrinsic kinetics of our Ni—P films. The EIS data for both HER and OER electrocatalysis can be simulated by a semi-empirical electrical equivalent circuit model shown in
The OER mechanism of the transformed Ni—P film was furthered studied by an investigation conducted in KOH of various concentrations. The polarization curves were collected in 1.0-5.0 M KOH (
the close match of
results in the unity of
(See Y. Surendranath, M. W. Kanan, D. G. Nocera, J. Am. Chem. Soc. 2010, 132, 16501-16509.) In other words, the OER reaction rate catalyzed by the Ni—P film is first order in the activity of hydroxide anion; therefore the limiting step is likely one hydroxide transfer, similar to the reported mechanism of “CoPi”. Id.
From the above results, it is natural to anticipate that the Ni—P film can be employed as a bifunctional electrocatalyst for overall water splitting. Indeed, when the as-prepared Ni—P films were used as electrocatalysts for both anode and cathode (a Ni—P/Ni—P catalyst couple), a catalytic current was observed when the applied potential was larger than 1.55V (
In summary, potentiodynamically deposited Ni—P films have been demonstrated to act as competent and bifunctional electrocatalysts for overall water splitting. The Ni—P film is unique because of the following reasons: (i) it is prepared via facile electrodeposition with low-cost regents under an ambient condition and can be directly employed as an electrocatalyst for both HER and OER without any post treatment; (ii) the catalytic activity of the Ni—P film can rival the state-of-the-art catalysts (i.e., Pt and IrO2), requiring an η=−93 mV for HER and η=344 mV for OER to reach a current density of 10 mA/cm2 with corresponding small Tafel slopes of 43 and 49 mV/dec, respectively; (iii) it can be utilized as catalysts for both anode and cathode of overall water splitting catalysis under strongly alkaline condition with superior efficiency and strong robustness. Various characterization and analytical techniques were applied to study the morphology and composition of the Ni—P film prior to and post electrocatalysis. It was concluded that the major component of the film is metallic nickel and nickel phosphide for the as-prepared and post-HER samples, whereas it was partially oxidized to nickel oxides/hydroxides/phosphates on the surface during OER. Kinetic analysis of its OER catalysis implied the limiting step is the transfer of one hydroxide group. Different from many reported hybrid systems, no conductive supports of high surface area, such as graphenes, carbon nanotubes, and nickel foams, were involved in the current system. The introduction of catalyst supports of high conductivity and large surface area will undoutedly further boost the catalytic performance of the Ni—P film, which is under our current pursuit.
In the following part of the present specification, numbered examples are listed which are directed to and which define advantageous embodiments. Said examples and embodiments belong to the present disclosure and description. The embodiments, examples, and features as listed, can separately or in groups, be combined in any manner to form embodiments belonging to the present disclosure.
Numbered Examples1. A catalyst, comprising a conductive substrate coated with a metal-phosphorus-derived film, wherein the metal is selected from the group consisting of Manganese, Iron, Cobalt, Nickel, and Copper.
2. The catalyst of example 1, wherein the conductive substrate comprises a material selected from the group consisting of copper, titanium, glassy carbon, fluorine-doped tin oxide, indium-doped tin oxide, tin, nickel, and stainless steel.
3. The catalyst of examples 1-2, wherein the metal-phosphorus-derived film is electrodeposited.
4. The catalyst of examples 1-3, wherein the metal-phosphorus-derived film comprises a cobalt-phosphorous-derived film.
5. The catalyst of examples 1-4, wherein the conductive substrate comprises a material selected from the group consisting of copper foil, nickel, and stainless steel.
6. The catalyst of examples 1-5, wherein the metal-phosphorus-derived film has a phosphorus concentration of greater than 0 to about 50%.
7. The catalyst of examples 1-5, wherein the metal-phosphorus-derived film has a phosphorus concentration of from about 5% to about 50%.
8. The catalyst of examples 1-5, wherein the metal-phosphorus-derived film has a phosphorus concentration of from about 5% to about 20%.
9. The catalyst of examples 1-5, wherein the metal-phosphorus-derived film has a phosphorus concentration of about 10%.
10. A method of producing hydrogen gas or oxygen gas, the method comprising:
providing a electrolysis solution, the electrolysis solution comprising water and an electrolyte;
inserting the catalyst of claim 1 into the electrolysis solution;
running an electric current through the catalyst.
11. The method of example 10, further comprising identifying and quantifying the hydrogen gas or oxygen gas.
12. The method of examples 10-11, further comprising collecting the hydrogen gas.
13. The method of examples 10-12, further comprising collecting the oxygen gas.
14. The method of examples 10-13, wherein the catalyst comprises a cobalt-phosphorous-derived film on a conductive substrate.
15. The method of examples 10-14, wherein the conductive substrate comprises copper foil.
16. The method of examples 10-15, wherein the electrolysis solution comprises an alkaline electrolyte.
17. The method of examples 10-16, wherein the electrolysis solutions is selected from the group consisting of KOH and NaOH.
18. A method of producing a catalyst, the method comprising:
providing a working electrode and a counter electrode, the working electrode and counter electrode each comprising a conductive substrate;
electrodepositing on the working electrode a metal-phosphorus-derived film, wherein the metal is selected from the group consisting of Manganese, Iron, Cobalt, Nickel, and Copper.
19. The method of example 18, wherein electrodepositing comprises:
-
- submersing the working electrode and the counter electrode in a deposition solution comprising a metal source that comprises Manganese, Iron, Cobalt, Nickel, or Copper and a phosphorus source, and
- cycling a current through the working electrode and counter electrode.
20. The method of examples 18-19, wherein:
the metal source comprises CoSO4 and
the phosphorus source comprises NaH2PO2.
21. The method of examples 18-20, wherein the current is cycled between a potential of −0.3 and −1.0 V vs Ag/AgCl.
It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also, various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art, and are also intended to be encompassed by the following claims.
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Claims
1. A catalyst, comprising a conductive substrate coated with a metal-phosphorus-derived film, wherein the metal is selected from the group consisting of Manganese, Iron, Cobalt, Nickel, and Copper.
2. The catalyst of claim 1, wherein the conductive substrate comprises a material selected from the group consisting of copper, titanium, glassy carbon, fluorine-doped tin oxide, indium-doped tin oxide, tin, nickel, and stainless steel.
3. The catalyst of claim 1, wherein the metal-phosphorus-derived film is electrodeposited.
4. The catalyst of claim 1, wherein the metal-phosphorus-derived film comprises a cobalt-phosphorous-derived film.
5. The catalyst of claim 1, wherein the conductive substrate comprises a material selected from the group consisting of copper foil, nickel, and stainless steel.
6. The catalyst of claim 1, wherein the metal-phosphorus-derived film has a phosphorus concentration of greater than 0 to about 50%.
7. The catalyst of claim 1, wherein the metal-phosphorus-derived film has a phosphorus concentration of from about 5% to about 50%.
8. The catalyst of claim 1, wherein the metal-phosphorus-derived film has a phosphorus concentration of from about 5% to about 20%.
9. The catalyst of claim 1, wherein the metal-phosphorus-derived film has a phosphorus concentration of about 10%.
10. A method of producing hydrogen gas or oxygen gas, the method comprising:
- providing a electrolysis solution, the electrolysis solution comprising water and an electrolyte;
- inserting the catalyst of claim 1 into the electrolysis solution;
- running an electric current through the catalyst.
11. The method of claim 10, further comprising identifying and quantifying the hydrogen gas or oxygen gas.
12. The method of claim 10, further comprising collecting the hydrogen gas.
13. The method of claim 10, further comprising collecting the oxygen gas.
14. The method of claim 10, wherein the catalyst comprises a cobalt-phosphorous-derived film on a conductive substrate.
15. The method of claim 10, wherein the conductive substrate comprises copper foil.
16. The method of claim 10, wherein the electrolysis solution comprises an alkaline electrolyte.
17. The method of claim 10, wherein the electrolysis solutions is selected from the group consisting of KOH and NaOH.
18. A method of producing a catalyst, the method comprising:
- providing a working electrode and a counter electrode, the working electrode and counter electrode each comprising a conductive substrate;
- electrodepositing on the working electrode a metal-phosphorus-derived film, wherein the metal is selected from the group consisting of Manganese, Iron, Cobalt, Nickel, and Copper.
19. The method of claim 18, wherein electrodepositing comprises:
- submersing the working electrode and the counter electrode in a deposition solution comprising a metal source that comprises Manganese, Iron, Cobalt, Nickel, or Copper and a phosphorus source, and
- cycling a current through the working electrode and counter electrode.
20. The method of claim 19, wherein:
- the metal source comprises CoSO4 and
- the phosphorus source comprises NaH2PO2.