Cobalt bismuth oxide materials and methods of use thereof

Abstract

Provided herein are mixed metal oxides comprising cobalt and bismuth, electrodes comprising the mixed metal oxides, method of preparing the mixed metal oxides and electrodes, devices comprising the same, and uses thereof.

Description

[0001] Atorney Docket No. 14722-013-228

[0002] COBALT BISMUTH OXIDE MATERIALS AND METHODS OF USE THEREOF

[0003]

[0001] This application claims the benefit of priority to U.S. Serial No. 63 / 693,983, filed September 12, 2024, which is incorporated herein by reference in its entirety.

[0004] 1. FIELD

[0005]

[0002] Provided herein are mixed metal oxides comprising cobalt and bismuth, electrodes comprising the mixed metal oxides, method of preparing the mixed metal oxides and electrodes, devices comprising the same, and uses thereof.

[0006] 2. BACKGROUND

[0007]

[0003] The oxygen evolution reaction (OER) supplies the protons and electrons needed to transform renewable electricity into chemicals and fuels. See, e.g., Chem. Rev. 2024, 124, 15, 9136-9223. However, the OER is kinetically sluggish. The reaction involves the multiple electron transfers and bond making / breaking steps, and generally operates at significant rates only when the applied potential far exceeds the reversible voltage. Historically, non-platinum group metal catalysts for OER operate at overpotentials averaging around 1.1 V. The relationship between overpotential and rate of catalysis is exponential. Additionally, the majority of catalysts that mediate OER tend to operate only in alkaline environments, due in part to challenges with identifying materials that have activity and stability in more corrosive acidic mediums.

[0008]

[0004] Provided herein are mixed metal oxides comprising cobalt and bismuth which are useful in the preparation of electrodes for the oxygen evolution reaction (OER). The electrodes perform in highly acidic environments (e.g. pH about 0), which is favorable for OER.

[0009] 3. SUMMARY

[0010]

[0005] Provided herein are mixed metal oxides comprising cobalt and bismuth. In certain embodiments, the mixed metal oxide comprises cobalt and bismuth in an atomic ratio of x (Co) to y (Bi), wherein x is greater than y, and preferably wherein the mixed metal oxide is stable at low pH (e.g. in a solution having a pH of between about 0 and about 2, a pH of about 0, a pH of about 1, or a pH of about 2). In certain embodiments, x is between about 0.60 and about 0.95, and y is between about 0.05 and about 0.40. In certain embodiments, x is between about 0.85

[0011] NAI-5002876540vl 1 Atorney Docket No. 14722-013-228 and about 0.90, and y is between about 0.10 and about 0.15. Tn certain embodiments, x is between about 0.63 and about 0.68 and y is between about 0.32 and about 0.37.

[0012]

[0006] Also provided herein are electrodes comprising a mixed metal oxide described herein, preferably wherein the electrode (i) is stable at low pH (e.g. in a solution having a pH of between about 0 and about 2, a pH of about 0, a pH of about 1, or a pH of about 2) and / or (ii) has an overpotential for water oxidation and / or oxygen evolution which is between about 300 and about 700 mV in a solution having a pH of 0. In certain embodiments, the electrode is an anode. In certain embodiments, the electrode is capable of oxidizing a fuel to convert chemical energy to electrical energy. In certain embodiments, the electrode is suitable for use as an electrode of an electrolyzer. In certain embodiments, the electrode is capable of oxidizing water at an applied potential. In certain embodiments, the electrode is capable of evolving oxygen at an applied potential. In certain embodiments, the electrode is capable of operating in an acidic solution.

[0013]

[0007] In certain embodiments, provided herein are methods of preparing a mixed metal oxide or an electrode described herein. In one embodiment, the method comprises depositing Co and Bi onto a substrate. In one embodiment, the depositing comprises sputtering Co and Bi onto the substrate. In one embodiment, the depositing comprises gradient physical vapor deposition (PVD) of Co and Bi onto the substrate.

[0014]

[0008] In certain embodiments, provided herein is an electrode prepared according to a method described herein.

[0015]

[0009] Also provided herein is an electrolyzer comprising an anode and a cathode. In one embodiment, the anode comprises a mixed metal oxide described herein. In one embodiment, the anode is an electrode described herein. In one embodiment, the electrolyzer is a water electrolyzer. In one embodiment, the electrolyzer is a hydrogen generator.

[0016]

[0010] Also provided herein is a solar or electrochemical fuels generator comprising an anode capable of oxidizing one or more protic compounds and a cathode capable of reducing CO2 and / or CO to produce a multi-carbon products. In one embodiment, the anode comprises a mixed metal oxide described herein. Tn one embodiment, the anode is an electrode described herein.

[0017] NAI-5002876540vl 2 Attorney Docket No. 14722-013-228

[0018] [Oil] Also provided herein is a solar or electrochemical ammonia generator comprising an anode capable of oxidizing one or more protic compounds and a cathode capable of reducing N2 to produce ammonia. In one embodiment, the anode comprises a mixed metal oxide described herein. In one embodiment, the anode is an electrode described herein.

[0019]

[0012] Also provided herein is a method of water oxidation comprising contacting an electrode or an electrolyzer described herein with an aqueous solution and applying an overpotential.

[0020]

[0013] Also provided herein is a method of oxygen evolution comprising contacting an electrode or an electrolyzer described herein with an aqueous solution and applying an overpotential.

[0021]

[0014] Also provided herein is a method of reducing and / or valorizing CO2 comprising: (a) oxidizing one or more protic compounds at a first electrode to release electrons, wherein the first electrode is an electrode described herein; and (b) reducing CO2 at a second electrode with the electrons released by oxidizing the one or more protic compounds at the first electrode. In one embodiment, step b produces one or more hydrocarbon products.

[0022]

[0015] Also provided herein is a method of reducing and / or valorizing CO comprising: (a) oxidizing one or more protic compounds at a first electrode to release electrons, wherein the first electrode is an electrode described herein; and (b) reducing CO at a second electrode with the electrons released by oxidizing the one or more protic compounds at the first electrode. In one embodiment, step b produces one or more hydrocarbon products.

[0023]

[0016] Also provided herein is a method of reducing N2 comprising: (a) oxidizing one or more protic compounds at a first electrode to release electrons, wherein the first electrode is an electrode described herein; and (b) reducing N2 at a second electrode with the electrons released by oxidizing the one or more protic compounds at the first electrode. In one embodiment, step b produces ammonia (NH3).

[0024]

[0017] Also provided herein is a method of producing NH3 comprising: (a) oxidizing one or more protic compounds at a first electrode to release electrons, wherein the first electrode is an electrode described herein; and (b) reducing N2 at a second electrode with the electrons released by oxidizing the one or more protic compounds at the first electrode.

[0025] NAI-5002876540vl 3 Attorney Docket No. 14722-013-228

[0026]

[0018] Also provided herein is a method of green hydrogen (H2) production comprising: (a) oxidizing one or more protic compounds at a first electrode to release electrons, wherein the first electrode is an electrode described herein; and (b) reducing protons (H+) or proton equivalents at a second electrode with the electrons released by oxidizing the one or more protic compounds at the first electrode.

[0027] 4. DETAILED DESCRIPTION

[0028] 4.1 Definition

[0029]

[0019] Unless specifically defined, any technical and / or scientific term used herein is intended to have the meaning commonly understood by an artisan skilled in the art of the field of invention.

[0030]

[0020] The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and / or the specification can mean “one”, but it is also consistent with the meaning of “one or more”, “at least one” and “one or more than one.”

[0031]

[0021] As used herein, the terms “comprising” and “including” can be used interchangeably. The terms “comprising” and “including” are to be interpreted as specifying the presence of the stated features or components as referred to, but does not preclude the presence or addition of one or more features, or components, or groups thereof. Additionally, the terms “comprising” and “including” are intended to include examples encompassed by the term “consisting of’. Consequently, the term “consisting of’ can be used in place of the terms “comprising” and “including” to provide for more specific embodiments of the invention.

[0032]

[0022] The term “consisting of’ means that a subject-matter has at least 90%, 95%, 97%, 98% or 99% of the stated features or components of which it consists. In another embodiment the term “consisting of’ excludes from the scope of any succeeding recitation any other features or components, excepting those that are not essential to the technical effect to be achieved.

[0033]

[0023] As used herein, the terms “or” is to be interpreted as an inclusive “or” meaning any one or any combination. Therefore, “A, B or C” means any of the following: “A; B; C; A and B; A and C; B and C; A, B and C”. An exception to this definition will occur only when a combination of elements, functions, steps or acts are in some way inherently mutually exclusive.

[0034] NAI-5002876540vl 4 Attorney Docket No. 14722-013-228

[0035]

[0024] As used herein, the term “between” includes the endpoint numbers on both limits of the range. For example, the range described by “between 3 and 5” is inclusive of the numbers “3” and “5”.

[0036]

[0025] As used herein, and unless otherwise indicated, the terms “about” and “approximately” are used to specify that the values given are approximate. For example, the term “about,” where it is used in connection with activation or reaction temperatures, denotes that temperature deviations within 30%, 25%, 20%, 15%, 10%, or 5% are encompassed by the temperature indicated. Similarly, the term “about,” where it is used in connection with activation or reaction time, denotes that time period deviations within 30%, 25%, 20%, 15%, 10%, or 5% are encompassed by the time period indicated.

[0037]

[0026] As used herein, and unless otherwise specified, the terms “about” and “approximately,” when used in connection with a numeric value or a range of values which is provided to characterize a particular mixed metal oxide or electrode (e.g., a ratio, an atomic molar density, a thickness, or an overpotential) indicate that the value or range of values may deviate to an extent deemed reasonable to one of ordinary skill in the art while still describing the particular mixed metal oxide or electrode. For example, in particular embodiments, the terms “about” and “approximately,” when used in this context, indicate that the numeric value or range of values may vary within 25%, 20%, 15%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1.5%, 1%, 0.5%, or 0.25% of the recited value or range of values. As used herein, a tilde (i.e., “~”) preceding a numerical value or range of values indicates “about” or “approximately.”

[0038]

[0027] Techniques for characterizing mixed metal oxide or electrode include, but are not limited to, thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray powder diffractometry (XRPD), X-ray spectroscopy, EPR spectroscopy, electrochemistry (e.g. cyclic voltammetry) magnetometry, optical microscopy, scanning electron microscopy (SEM), electron crystallography and quantitative analysis, Energy Dispersive Spectroscopy (EDS), Inductively coupled plasma mass spectrometry (ICP-MS), and elemental analysis. Techniques useful for analyzing powder diffraction data include profile refinement, such as Rietveld refinement, which may be used, e.g., to analyze diffraction peaks associated with a single phase in a sample comprising more than one solid phase. Other methods useful for analyzing powder

[0039] NAI-5002876540vl 5 Atorney Docket No. 14722-013-228 diffraction data include unit cell indexing, which allows one of skill in the art to determine unit cell parameters from a sample comprising crystalline powder.

[0040]

[0028] Mixed metal oxides or electrodes may exhibit distinct physical characterization data that are unique to a particular mixed metal oxide or electrode. These characterization data may be obtained by various techniques known to those skilled in the art, including for example differential scanning calorimetry, thermal gravimetric analysis, electrochemistry (e.g. cyclic voltammetry), energy dispersive spectroscopy (EDS), and inductively coupled plasma mass spectrometry (ICP-MS). The data provided by these techniques may be used to identify a mixed metal oxide or electrode. One skilled in the art can determine whether a mixed metal oxide or electrode is one of the mixed metal oxides or electrodes provided herein by performing one of these characterization techniques and determining whether the resulting data “matches” the reference data provided herein, which is identified as being characteristic of a particular mixed metal oxide or electrode. Characterization data that “matches” those of a reference mixed metal oxide or electrode is understood by those skilled in the art to correspond to the same mixed metal oxide or electrode as the reference mixed metal oxide or electrode. In analyzing whether data “match,” a person of ordinary skill in the art understands that particular characterization data points may vary to a reasonable extent while still describing a given mixed metal oxide or electrode, due to, for example, experimental error and routine sample-to-sample analysis variation.

[0041]

[0029] As used herein, and unless otherwise specified, the “Oxygen Evolution Assay” comprises electrolysis of water in a three-electrode set up, wherein the working electrode comprises a mixed metal oxide described herein, the counter electrode is a coiled Pt wire in about 0.1 M H2SO4 electrolyte solution, and the reference electrode is a leakfree silver-silver chloride reference electrode in about 1 M H2SO4, and wherein the electrolyte solution is an about 1 M H2SO4 solution, and wherein the working electrode and the counter electrode are separated by a bipolar membrane to minimize potential cross-contamination, and wherein electrolysis is conducted at a continuous applied geometric current density of lOmA / cm2.

[0042]

[0030] The disclosure can be understood more fully by reference to the following detailed description and illustrative examples, which are intended to exemplify non-limiting embodiments.

[0043] NAI-5002876540vl 6 Atorney Docket No. 14722-013-228

[0044] 4.2 Electrode Materials

[0045]

[0031] In some embodiments, provided herein are mixed metal oxides comprising cobalt and bismuth. In some embodiments, provided herein are electrodes comprising a mixed metal oxide described herein.

[0046] Mixed Metal Oxides

[0047]

[0032] In some embodiments, provided herein is a mixed metal oxide comprising cobalt and bismuth in an atomic ratio of x (Co) to y (Bi), wherein x is greater than y. In one embodiment, x is between about 0.60 and about 0.95, and y is between about 0.05 and about 0.40. In one embodiment, x is between about 0.80 and about 0.95. In one embodiment, x is between about 0.85 and about 0.90. In one embodiment, x is about 0.85, about 0.86, about 0.87, about 0.88, about 0.89, or about 0.90. In one embodiment, y is between about 0.05 and 0.20. In one embodiment, y is between about 0.10 and about 0.15. In one embodiment, y is about 0.10, about 0.11, about 0.12, about 0.13, about 0.14, or about 0.15. In one embodiment, x is between about 0.80 and about 0.95 and y is between about 0.05 and 0.20. In one embodiment, x is between about 0.85 and about 0.90 and y is between about 0.10 and about 0.15. In one embodiment, x is between about 0.60 and about 0.70. In one embodiment, x is between about 0.63 and about 0.68. In one embodiment, x is about 0.63, about 0.64, about 0.65, about 0.66, about 0.67, or about 0.68. In one embodiment, y is between about 0.30 and about 0.40. In one embodiment, y is between about 0.32 and about 0.37. In one embodiment, y is about 0.32, about 0.33, about 0.34, about 0.35, about 0.36, or about 0.37. In one embodiment, x is between about 0.60 and about 0.70 and y is between about 0.30 and about 0.40. In one embodiment, x is between about 0.63 and about 0.68 and y is between about 0.32 and about 0.37. In certain embodiments, the mixed metal oxide comprises oxygen in an atomic ratio of oxygen (O) to cobalt and bismuth (Co + Bi) which is between about 1 and about 1.5. In certain embodiments, the mixed metal oxide consist of, or consists essentially of, cobalt, bismuth, and oxygen. In certain embodiments, the atomic ratio of a mixed metal oxide described herein has been determined by Energy Dispersive Spectroscopy (EDS).

[0048]

[0033] In certain embodiments, a mixed metal oxide described herein has an atomic molar density which is between about 0.002 mol / cm2and about 0.2 mol / cm2. In one embodiment, the atomic molar density is between about 0.005 mol / cm2and about 0.1 mol / cm2. In one

[0049] NAI-5002876540vl 7 Atorney Docket No. 14722-013-228 embodiment, the atomic molar density is between about 0.008 mol / cm2and about 0.08 mol / cm2. In one embodiment, the atomic molar density is the atomic molar density of Co, Bi, or O, or combinations thereof, in the mixed metal oxide.

[0050]

[0034] In certain embodiments, a mixed metal oxide described herein is stable at low pH. In one embodiment, the mixed metal oxide is stable in a solution having a pH which is between about -1 and about 2. In one embodiment, the mixed metal oxide is stable in a solution having a pH which is between about 0 and about 2. In one embodiment, the mixed metal oxide is stable in a solution having a pH which is about -1, about 0, about 1, or about 2. In one embodiment, the mixed metal oxide is stable in a solution having a pH which is between about -1 and about 1. In one embodiment, the mixed metal oxide is stable in a solution having a pH which is about 0. In one embodiment, the mixed metal oxide is stable as a layer of an electrode for at least 30 minutes in a solution having a pH between about -1 and about 1, as determined by Oxygen Evolution Assay. In one embodiment, the mixed metal oxide is stable as a layer of an electrode for at least 30 minutes in a solution having a pH of about 0, as determined by Oxygen Evolution Assay. In one embodiment, the mixed metal oxide is stable as a layer of an electrode for at least 4 hours in a solution having a pH between about -1 and about 1, as determined by Oxygen Evolution Assay. In one embodiment, the mixed metal oxide is stable as a layer of an electrode for at least 4 hours in a solution having a pH of about 0, as determined by Oxygen Evolution Assay. In one embodiment, the mixed metal oxide is stable as a layer of an electrode for at least 30 minutes in a solution of about 1 M H2SO4, as determined by Oxygen Evolution Assay. In one embodiment, the mixed metal oxide is stable as a layer of an electrode for at least 4 hours in a solution of about 1 M H2SO4, as determined by Oxygen Evolution Assay. In one embodiment, the mixed metal oxide is stable as a layer of an electrode for at least 30 minutes at a continuous applied geometric current density of about 10 mA / cm2, as determined by Oxygen Evolution Assay. In one embodiment, the mixed metal oxide is stable as a layer of an electrode for at least 4 hours at a continuous applied geometric current density of about 10 mA / cm2, as determined by Oxygen Evolution Assay. In one embodiment, the mixed metal oxide is stable as a layer of an electrode for at least 30 minutes in a solution having a pH between about -1 and about 1, and at a continuous applied geometric current density of about 10 mA / cm2, as determined by Oxygen Evolution Assay. In one embodiment, the mixed metal oxide is stable as a layer of an electrode for at least 30 minutes in a solution having a pH of about 0, and at a continuous applied

[0051] NAI-5002876540vl 8 Atorney Docket No. 14722-013-228 geometric current density of about 10 mA / cm2, as determined by Oxygen Evolution Assay. In one embodiment, the mixed metal oxide is stable as a layer of an electrode for at least 4 hours in a solution having a pH between about -1 and about 1, and at a continuous applied geometric current density of about 10 mA / cm2, as determined by Oxygen Evolution Assay. In one embodiment, the mixed metal oxide is stable as a layer of an electrode for at least 4 hours in a solution having a pH of about 0, and at a continuous applied geometric current density of about 10 mA / cm2, as determined by Oxygen Evolution Assay. In one embodiment, the mixed metal oxide is stable as a layer of an electrode for at least 30 minutes in a solution of about 1 M H2SO4 at a continuous applied geometric current density of about 10 mA / cm2, as determined by Oxygen Evolution Assay. In one embodiment, the mixed metal oxide is stable as a layer of an electrode for at least 4 hours in a solution of about 1 M H2SO4 at a continuous applied geometric current density of about 10 mA / cm2, as determined by Oxygen Evolution Assay. In certain embodiments, the mixed metal oxide is stable as a layer of an electrode which maintains a continuous applied geometric current density of at least 10 mA / cm2for at least 30 minutes at an overpotential for evolution of oxygen of between about 300 and about 700 mV in a solution having a pH between about -1 and about 1. In certain embodiments, the mixed metal oxide is stable as a layer of an electrode which maintains a continuous applied geometric current density of at least 10 mA / cm2for at least 30 minutes at an overpotential for evolution of oxygen of between about 300 and about 700 mV in a solution having a pH of about 0. In one embodiment, the mixed metal oxide is stable as a layer of an electrode which maintains a continuous applied geometric current density of at least 10 mA / cm2for at least 4 hours at an overpotential for evolution of oxygen of between about 300 and about 700 mV in a solution having a pH between about -1 and about 1. In one embodiment, the mixed metal oxide is stable as a layer of an electrode which maintains a continuous applied geometric current density of at least 10 mA / cm2for at least 4 hours at an overpotential for evolution of oxygen of between about 300 and about 700 mV in a solution having a pH of about 0. In one embodiment, the mixed metal oxide is stable as a layer of an electrode which maintains a continuous applied geometric current density of at least 10 mA / cm2for at least 30 minutes at an overpotential for evolution of oxygen of between about 300 and about 700 mV in a solution of about 1 M H2SO4. In one embodiment, the mixed metal oxide is stable as a layer of an electrode which maintains a continuous applied

[0052] NAI-5002876540vl 9 Atorney Docket No. 14722-013-228 geometric current density of at least 10 mA / cm2for at least 4 hours at an overpotential for evolution of oxygen of between about 300 and about 700 mV in a solution of about 1 M H2SO4.

[0053]

[0035] In certain embodiments, a mixed metal oxide described herein is substantially pure. In certain embodiments, a mixed metal oxide described herein is substantially chemically pure. In certain embodiments, a mixed metal oxide described herein is substantially physically pure.

[0054] Electrodes

[0055]

[0036] In certain embodiments, provided herein is an electrode comprising a mixed metal oxide described herein. In one embodiment, the electrode is an anode.

[0056]

[0037] In one embodiment, the electrode is capable of oxidizing a fuel to convert chemical energy to electrical energy. In one embodiment, the fuel is H2, NH3, or a hydrocarbon.

[0057]

[0038] In one embodiment, the electrode is suitable for use as an electrode of an electrolyzer. In one embodiment, the electrode is an electrode of an electrolyzer. In one embodiment, the electrode is capable of oxidizing one or more protic compounds at an applied potential. In one embodiment, the electrode is capable of oxidizing water at an applied potential. In one embodiment, the electrode is capable of evolving oxygen at an applied potential.

[0058]

[0039] In one embodiment, the electrode is capable of operating in an acidic solution. In one embodiment, the electrode is capable of operating in an acidic aqueous solution. In one embodiment, the acidic aqueous solution has a pH of between about -1 and about 2. In one embodiment, the acidic aqueous solution has a pH of between about 0 and about 2. In one embodiment, the acidic aqueous solution is an about 0.1 to 10 M solution of an acid. In embodiment, the acid is hydrochloric acid, hydrobromic acid, nitric acid, phosphoric acid, or sulfuric acid In one embodiment, the acidic aqueous solution is an about 1 M solution of sulfuric acid (H2SO4).

[0059]

[0040] In certain embodiments, an electrode described herein further comprises an electroactive substrate.

[0060]

[0041] In one embodiment, the electroactive substrate is a carbon-based substrate. In one embodiment, the electroactive substrate is a silicon-based substrate. In one embodiment, the silicon-based substrate is a silicon wafer. In one embodiment, the silicon-based substrate has a thickness which is between about 0.1 and about 10 mm. In one embodiment, the thickness of the

[0061] NAI-5002876540vl 10 Atorney Docket No. 14722-013-228 silicon-based substrate is between about 0.5 and about 1 mm. In one embodiment, the thickness of the silicon-based substrate is between about 0.7 and about 0.8 mm.

[0062]

[0042] In one embodiment, the electroactive substrate comprises a layer of SiCh. In one embodiment, the layer of SiCh has a thickness which is greater than 100 nm. In one embodiment, the thickness of the SiCh layer is between about 100 nm and about 1 mm. In one embodiment, the thickness of the SiCh layer is between about 100 nm and about 800 nm. In one embodiment, the thickness of the SiCh layer is between about 100 nm and about 500 nm.

[0063]

[0043] In one embodiment, the electroactive substrate comprises a layer of titanium (Ti). In one embodiment, the layer of Ti has a thickness which is between about 1 nm and about 25 nm. In one embodiment, the thickness of the Ti layer is between about 5 nm and about 15 nm.

[0064]

[0044] In one embodiment, the electroactive substrate comprises a layer of platinum (Pt). In one embodiment, the layer of Pt has a thickness which is between about 10 nm and about 100 nm. In one embodiment, the thickness of the layer of Pt is between about 40 and about 60 nm.

[0065]

[0045] In one embodiment, the electrode comprises a layer of the mixed metal oxide having a thickness which is between about 10 nm and about 100 nm. In one embodiment, the thickness of the layer of the mixed metal oxide is between about 40 nm and about 80 nm.

[0066]

[0046] In one embodiment, the electrode comprises, in order from top to bottom, a layer of the mixed metal oxide and the electroactive substrate. In one embodiment, the electrode does not comprise tin (Sn). In one embodiment, the electrode comprises, in order from top to bottom, a layer of the mixed metal oxide, a layer of Pt, a layer of Ti, a layer of SiCh, and a silicon wafer. In one embodiment, (a) the layer of the mixed metal oxide has a thickness which is between about 10 nm and about 100 nm; and / or (b) the layer of Pt has a thickness which is between about 10 nm and about 100 nm; and / or (c) the layer of Ti has a thickness which is between about 1 nm and about 25 nm; and / or (d) the layer of SiCh has a thickness which is greater than 100 nm; and / or (e) the silicon wafer has a thickness which is between about 0.1 and about 10 mm. In one embodiment, (a) the thickness of the layer of the mixed metal oxide is between about 40 nm and about 80 nm; and / or (b) the thickness of the layer of Pt is between about 40 and about 60 nm; and / or (c) the thickness of the Ti layer is between about 5 nm and about 15 nm; and / or (d) the thickness of the SiCh layer is between about 100 nm and about 1 mm; and / or (e) the thickness of the silicon-based substrate is between about 0.5 and about 1 mm. In one embodiment, (a) the

[0067] NAI-5002876540vl 11 Atorney Docket No. 14722-013-228 thickness of the layer of the mixed metal oxide is between about 40 nm and about 80 nm; and / or (b) the thickness of the layer of Pt is between about 40 and about 60 nm; and / or (c) the thickness of the Ti layer is between about 5 nm and about 15 nm; and / or (d) the thickness of the SiCh layer is between about 100 nm and about 1 mm; and / or (e) the thickness of the silicon-based substrate is between about 0.7 and about 0.8 mm.

[0068]

[0047] In certain embodiments, the electrode has been prepared by a method described herein. In one embodiment, the electrode has been prepared by depositing Co and Bi onto the electroactive substrate. In one embodiment, the depositing comprises sputtering Co and Bi onto the electroactive substrate. In one embodiment, the depositing comprises gradient physical vapor deposition (PVD) of Co and Bi onto the electroactive substrate. In one embodiment, the electrode has not been annealed via heat treatment after the depositing of Co and Bi onto the electroactive substrate. In one embodiment, the electrode has been annealed via heat treatment after the depositing of Co and Bi onto the electroactive substrate. In one embodiment, the electrode has been annealed at a temperature which is between about 500 and about 600 °C, for a period which is between about 1 and about 5 hours, in a box furnace in air, after the depositing of Co and Bi onto the electroactive substrate. In one embodiment, the electrode has been annealed at a temperature of about 500 °C, for a period which is between about 1 and about 5 hours, in a box furnace in air, after the depositing of Co and Bi onto the electroactive substrate. In one embodiment, the electrode has been annealed at a temperature of about 600 °C, for a period which is between about 1 and about 5 hours, in a box furnace in air, after the depositing of Co and Bi onto the electroactive substrate.

[0069]

[0048] In certain embodiments, the electrode is stable at low pH. In one embodiment, the electrode is stable in a solution having a pH which is between about -1 and about 2. In one embodiment, the electrode is stable in a solution having a pH which is between about 0 and about 2. In one embodiment, the electrode is stable in a solution having a pH which is about -1, about 0, about 1, or about 2. In one embodiment, the electrode is stable in a solution having a pH which is about 0. In certain embodiments, the electrode is stable for at least 30 minutes in a solution having a pH between about -1 and about 1, as determined by Oxygen Evolution Assay. In certain embodiments, the electrode is stable for at least 30 minutes in a solution having a pH of about 0, as determined by Oxygen Evolution Assay. In one embodiment, the electrode is stable for at least 4 hours in a solution having a pH between about -1 and about 1, as determined

[0070] NAI-5002876540vl 12 Atorney Docket No. 14722-013-228 by Oxygen Evolution Assay. Tn one embodiment, the electrode is stable for at least 4 hours in a solution having a pH of about 0, as determined by Oxygen Evolution Assay. In one embodiment, the electrode is stable for at least 30 minutes in a solution of about 1 M H2SO4, as determined by Oxygen Evolution Assay. In one embodiment, the electrode is stable for at least 4 hours in a solution of about 1 M H2SO4, as determined by Oxygen Evolution Assay. In one embodiment, the electrode is stable for at least 30 minutes at a continuous applied geometric current density of about 10 mA / cm2, as determined by Oxygen Evolution Assay. In one embodiment, the electrode is stable for at least 4 hours at a continuous applied geometric current density of about 10 mA / cm2, as determined by Oxygen Evolution Assay. In one embodiment, the electrode is stable for at least 30 minutes in a solution having a pH between about -1 and about 1, and at a continuous applied geometric current density of about 10 mA / cm2, as determined by Oxygen Evolution Assay. In one embodiment, the electrode is stable for at least 30 minutes in a solution having a pH of about 0, and at a continuous applied geometric current density of about 10 mA / cm2, as determined by Oxygen Evolution Assay. In one embodiment, the electrode is stable for at least 4 hours in a solution having a pH between about -1 and about 1, and at a continuous applied geometric current density of about 10 mA / cm2, as determined by Oxygen Evolution Assay. In one embodiment, the electrode is stable for at least 4 hours in a solution having a pH of about 0, and at a continuous applied geometric current density of about 10 mA / cm2, as determined by Oxygen Evolution Assay. In one embodiment, the electrode is stable for at least 30 minutes in a solution of about 1 M H2SO4 at a continuous applied geometric current density of about 10 mA / cm2, as determined by Oxygen Evolution Assay. In one embodiment, the electrode is stable for at least 4 hours in a solution of about 1 M H2SO4 at a continuous applied geometric current density of about 10 mA / cm2, as determined by Oxygen Evolution Assay.

[0071]

[0049] In certain embodiments, the electrode maintains a continuous applied geometric current density of at least 10 mA / cm2for at least 30 minutes at an overpotential for evolution of oxygen of between about 300 and about 700 mV in a solution having a pH between about -1 and about 1. In certain embodiments, the electrode maintains a continuous applied geometric current density of at least 10 mA / cm2for at least 30 minutes at an overpotential for evolution of oxygen of between about 300 and about 700 mV in a solution having a pH of 0. In one embodiment, the electrode maintains a continuous applied geometric current density of at least 10 mA / cm2for at

[0072] NAI-5002876540vl 13 Atorney Docket No. 14722-013-228 least 4 hours at an overpotential for evolution of oxygen of between about 300 and about 700 mV in a solution having a pH between about -1 and about 1. In one embodiment, the electrode maintains a continuous applied geometric current density of at least 10 mA / cm2for at least 4 hours at an overpotential for evolution of oxygen of between about 300 and about 700 mV in a solution having a pH of 0. In one embodiment, the electrode maintains a continuous applied geometric current density of at least 10 mA / cm2for at least 30 minutes at an overpotential for evolution of oxygen of between about 300 and about 700 mV in a solution of about 1 M H2SO4. In one embodiment, the electrode maintains a continuous applied geometric current density of at least 10 mA / cm2for at least 4 hours at an overpotential for evolution of oxygen of between about 300 and about 700 mV in a solution of about 1 M H2SO4.

[0073]

[0050] In certain embodiments, the electrode has an overpotential for water oxidation and / or oxygen evolution of less than 700 mV. In one embodiment, the electrode has an overpotential for water oxidation and / or oxygen evolution of less than 600 mV. In one embodiment, the electrode has an overpotential for water oxidation and / or oxygen evolution of less than 500 mV. In one embodiment, the electrode has an overpotential for water oxidation and / or oxygen evolution of less than 400 mV. In one embodiment, the electrode has an overpotential for water oxidation and / or oxygen evolution of between about 300 and about 700 mV. In one embodiment, the electrode has an overpotential for water oxidation and / or oxygen evolution of between about 400 and about 700 mV. In one embodiment, the electrode has an overpotential for water oxidation and / or oxygen evolution of between about 450 and about 650 mV. In one embodiment, the overpotential is for water oxidation and / or oxygen evolution conducted in a solution having low pH. In one embodiment, the overpotential is for water oxidation and / or oxygen evolution conducted in a solution having a pH of between about -1 and about 2. In one embodiment, the overpotential is for water oxidation and / or oxygen evolution conducted in a solution having a pH of between about 0 and about 2. In one embodiment, the overpotential is for water oxidation and / or oxygen evolution conducted in a solution having a pH of about -1, about 0, about 1, or about 2. In one embodiment, the overpotential is for water oxidation and / or oxygen evolution conducted in a solution having a pH of about -1, about 0, about 1, or about 2.

[0074] 4.3 Methods of Production

[0075] NAI-5002876540vl 14 Attorney Docket No. 14722-013-228

[0076]

[0051] In certain embodiments, provided herein are methods of preparing a mixed metal oxide or an electrode described herein. In certain embodiments, a mixed metal oxide or an electrode described herein is prepared by a method selected from the group consisting of sol-gel synthesis, hydrothermal or solvothermal synthesis, co-precipitation (e.g. from a solution of metal salts upon addition of a base), solid-state synthesis (e.g. mixing solid metal salt precursors and heating at high temperatures to form the desired mixed oxide), chemical vapor deposition (e.g. atomic vapor deposition), and physical vapor deposition. Other methods for preparing mixed metal oxide materials and / or electrodes are known in the art, and can also be used for preparing a mixed metal oxide or an electrode described herein.

[0077]

[0052] In one embodiment, the method comprises depositing Co and Bi onto a substrate. In one embodiment, the depositing comprises sputtering Co and Bi onto the substrate. In one embodiment, the depositing comprises physical vapor deposition (PVD) of Co and Bi onto the substrate. In one embodiment, the depositing comprises gradient physical vapor deposition (PVD) of Co and Bi onto the substrate. In one embodiment, the depositing comprises chemical vapor deposition (CVD) of Co and Bi onto the substrate. In one embodiment, the depositing comprises atomic vapor deposition (AVD) of Co and Bi onto the substrate.

[0078]

[0053] In one embodiment, the method does not comprise annealing the mixed metal oxide via heat treatment after the depositing step. In one embodiment, the method comprises annealing the mixed metal oxide via heat treatment after the depositing step. In one embodiment, annealing is conducted at a temperature which is between about 500 and about 600 °C, for a period which is between about 1 and about 5 hours, in a box furnace in air. In one embodiment, annealing is conducted at a temperature of about 500 °C, for a period which is between about 1 and about 5 hours, in a box furnace in air. In one embodiment, annealing is conducted at a temperature of about 600 °C, for a period which is between about 1 and about 5 hours, in a box furnace in air.

[0079]

[0054] In one embodiment, the method results in a layer of the mixed metal oxide having a thickness which is between about 10 nm and about 100 nm. In one embodiment, the method results in a layer of the mixed metal oxide having a thickness which is between about 40 nm and about 80 nm.

[0080] NAI-5002876540vl 15 Atorney Docket No. 14722-013-228

[0081]

[0055] In one embodiment, the substrate is an electroactive substrate. In one embodiment, the substrate comprises a layer of silicon. In one embodiment, the layer of silicon is a silicon wafer. In one embodiment, the layer of silicon has a thickness which is between about 0.1 and about 10 mm. In one embodiment, the thickness of the layer of silicon is between about 0.5 and about 1 mm. In one embodiment, the thickness of the layer of silicon is between about 0.7 and about 0.8 mm. In one embodiment, the substrate comprises a layer of SiCh. In one embodiment, the layer of SiCh has a thickness which is greater than 100 nm. In one embodiment, the thickness of the SiCh layer is between about 100 nm and about 1 mm. In one embodiment, the thickness of the SiCh layer is between about 100 nm and about 800 nm. In one embodiment, the thickness of the SiCh layer is between about 100 nm and about 500 nm. In one embodiment, the substrate comprises a layer of titanium (Ti). In one embodiment, the layer of Ti has a thickness which is between about 1 nm and about 25 nm. In one embodiment, the thickness of the Ti layer is between about 5 nm and about 15 nm. In one embodiment, the substrate comprises a layer of platinum (Pt). In one embodiment, the layer of Pt has a thickness which is between about 10 nm and about 100 nm. In one embodiment, the thickness of the layer of Pt is between about 40 and about 60 nm.

[0082]

[0056] In one embodiment, the substrate comprises, in order from top to bottom, a layer of Pt, a layer of Ti, a layer of SiCh, and a silicon wafer. In one embodiment, (a) the layer of Pt has a thickness which is between about 10 nm and about 100 nm; and / or (b) the layer of Ti has a thickness which is between about 1 nm and about 25 nm; and / or (c) the layer of SiCh has a thickness which is greater than 100 nm; and / or (d) the silicon wafer has a thickness which is between about 0.1 and about 10 mm. In one embodiment, (a) the thickness of the layer of Pt is between about 40 and about 60 nm; and / or (b) the thickness of the Ti layer is between about 5 nm and about 15 nm; and / or (c) the thickness of the SiCh layer is between about 100 nm and about 1 mm; and / or (d) the thickness of the silicon-based substrate is between about 0.5 and about 1 mm. In one embodiment, (a) the thickness of the layer of Pt is between about 40 and about 60 nm; and / or (b) the thickness of the Ti layer is between about 5 nm and about 15 nm; and / or (c) the thickness of the SiCh layer is between about 100 nm and about 1 mm; and / or (d) the thickness of the silicon-based substrate is between about 0.7 and about 0.8 mm.

[0083]

[0057] In one embodiment, the method results in the layer of the mixed metal oxide being deposited on top of the substrate.

[0084] NAI-5002876540vl 16 Attorney Docket No. 14722-013-228

[0085] 4.4 Devices

[0086]

[0058] In certain embodiments, a mixed metal oxide or electrode described herein can be employed in an electrolyzer, a solar or electrochemical fuels generator, a reversible fuel cell, and / or a reversible air battery. In other embodiments, a mixed metal oxide or electrode described herein can be employed in an electrochemical sensor or an electrochemical capacitor (e.g. a supercapacitor).

[0087]

[0059] In certain embodiments, provided herein is an electrolyzer comprising an anode and a cathode. In one embodiment, the anode comprises a mixed metal oxide described herein. In one embodiment, the anode is an electrode described herein. In one embodiment, the cathode comprises a suitable reduction catalyst known in the art, including but are not limited to Cu, Ni, Pt, NiMo, and NiCo.

[0088]

[0060] In one embodiment, the electrolyzer further comprises a reservoir. In one embodiment, the anode and the cathode are positioned in or adjacent to the reservoir. In one embodiment, a medium is positioned in the reservoir such that the anode and the cathode are in contact with the medium. In one embodiment, the medium comprises an aqueous solution. In one embodiment, the medium comprises an acidic aqueous solution. In one embodiment, the acidic aqueous solution has a pH of between about -1 and about 2. In one embodiment, the acidic aqueous solution has a pH of between about 0 and about 2. In one embodiment, the medium comprises an acid. In one embodiment, the medium is acidic. In one embodiment, the medium has a pH of between about -1 and about 2. In one embodiment, the medium has a pH of between about 0 and about 2. In one embodiment, the acidic aqueous solution is an about 0.1 to 10 M solution of an acid. In embodiment, the acid is hydrochloric acid, hydrobromic acid, nitric acid, phosphoric acid, or sulfuric acid. In one embodiment, the acidic aqueous solution is an about 1 M solution of sulfuric acid (H2SO4).

[0089]

[0061] In another embodiment, the electrolyzer comprises a first reservoir and a second reservoir. In one embodiment, the first reservoir and the second reservoir are separated by a membrane. In one embodiment, the membrane is a membrane known in the art to be suitable for use in electrochemical systems having two or more cells. In one embodiment, the anode is positioned in or adjacent to the first reservoir. In one embodiment, the cathode is positioned in or adjacent to the second reservoir. In one embodiment, a medium is independently positioned

[0090] NAI-5002876540vl 17 Attorney Docket No. 14722-013-228 in the first reservoir and the second reservoir such that the anode and the cathode are each in contact with a medium. In one embodiment, the medium positioned in the first reservoir and the second reservoir are the same medium. In one embodiment, the medium positioned in the first reservoir and the second reservoir are different media. In one embodiment, the anode is positioned in or adjacent to the first reservoir and is in contact with an acidic medium. In one embodiment, the acidic medium comprises an acidic aqueous solution. In one embodiment, the acidic medium comprises an acid. In one embodiment, the acidic aqueous solution has a pH of between about -1 and about 2. In one embodiment, the acidic aqueous solution has a pH of between about 0 and about 2. In one embodiment, the medium has a pH of between about -1 and about 2. In one embodiment, the medium has a pH of between about 0 and about 2. In one embodiment, the acidic aqueous solution is an about 0.1 to 10 M solution of an acid. In embodiment, the acid is hydrochloric acid, hydrobromic acid, nitric acid, phosphoric acid, or sulfuric acid. In one embodiment, the acidic aqueous solution is an about 1 M solution of sulfuric acid (H2SO4).

[0091]

[0062] In one embodiment, the cathode and anode of the electrolyzer are connected to a voltage source capable of applying an overpotential. In one embodiment, the voltage source can be any voltage source known in the art, for example a photovoltaic voltage source, a battery, or another electronic device.

[0092]

[0063] In one embodiment, the electrolyzer is a water electrolyzer. In one embodiment, the electrolyzer is a hydrogen generator.

[0093]

[0064] In certain embodiments, provided herein is a solar or electrochemical fuels generator comprising an anode capable of oxidizing one or more protic compounds and a cathode capable of reducing CO2 and / or CO to produce a multi-carbon products. In one embodiment, the anode comprises a mixed metal oxide described herein. In one embodiment, the anode is an electrode described herein. In one embodiment, the cathode comprises a suitable reduction catalyst known in the art, including but are not limited to Cu, Ni, Pt, NiMo, and NiCo. In one embodiment, the one or more protic compounds is or comprises water.

[0094]

[0065] In one embodiment, the solar or electrochemical fuels generator further comprises a first reservoir and a second reservoir. In one embodiment, the first reservoir and the second reservoir are separated by a membrane. In one embodiment, the membrane is a membrane

[0095] NAI-5002876540vl 18 Attorney Docket No. 14722-013-228 known in the art to be suitable for use in electrochemical systems having two or more cells. In one embodiment, the anode is positioned in or adjacent to the first reservoir. In one embodiment, the cathode is positioned in or adjacent to the second reservoir. In one embodiment, a medium is independently positioned in the first reservoir and the second reservoir such that the anode and the cathode are each in contact with a medium. In one embodiment, the medium positioned in the first reservoir and the second reservoir are the same medium. In one embodiment, the medium positioned in the first reservoir and the second reservoir are different media. In one embodiment, the anode is positioned in or adjacent to the first reservoir and is in contact with an acidic medium. In one embodiment, the acidic medium comprises an acidic aqueous solution. In one embodiment, the acidic medium comprises an acid. In one embodiment the acidic aqueous solution has a pH of between about -1 and about 2. In one embodiment the acidic aqueous solution has a pH of between about 0 and about 2. In one embodiment the medium has a pH of between about -1 and about 2. In one embodiment the medium has a pH of between about 0 and about 2. In one embodiment, the acidic aqueous solution is an about 0.1 to 10 M solution of an acid. In embodiment, the acid is hydrochloric acid, hydrobromic acid, nitric acid, phosphoric acid, or sulfuric acid. In one embodiment, the acidic aqueous solution is an about 1 M solution of sulfuric acid (H2SO4).

[0096]

[0066] In one embodiment, the cathode and anode of the solar or electrochemical fuels generator are connected to a voltage source capable of applying an overpotential. In one embodiment, the voltage source can be any voltage source known in the art, for example a photovoltaic voltage source, a battery, or another electronic device.

[0097]

[0067] In certain embodiments, provided herein is a solar or electrochemical ammonia generator comprising an anode capable of oxidizing one or more protic compounds and a cathode capable of reducing N2 to produce ammonia. In one embodiment, the anode comprises a mixed metal oxide described herein. In one embodiment, the anode is an electrode described herein. In one embodiment, the cathode comprises a suitable reduction catalyst known in the art, including but are not limited to Cu, Ni, Pt, NiMo, and NiCo. In one embodiment, the one or more protic compounds is or comprises water.

[0098]

[0068] In one embodiment, the solar or electrochemical ammonia generator further comprises a first reservoir and a second reservoir. In one embodiment, the first reservoir and the

[0099] NAI-5002876540vl 19 Atorney Docket No. 14722-013-228 second reservoir are separated by a membrane. In one embodiment, the membrane is a membrane known in the art to be suitable for use in electrochemical systems having two or more cells. In one embodiment, the anode is positioned in or adjacent to the first reservoir. In one embodiment, the cathode is positioned in or adjacent to the second reservoir. In one embodiment, a medium is independently positioned in the first reservoir and the second reservoir such that the anode and the cathode are each in contact with a medium. In one embodiment, the medium positioned in the first reservoir and the second reservoir are the same medium. In one embodiment, the medium positioned in the first reservoir and the second reservoir are different media. In one embodiment, the anode is positioned in or adjacent to the first reservoir and is in contact with an acidic medium. In one embodiment, the acidic medium comprises an acidic aqueous solution. In one embodiment, the acidic medium comprises an acid. In one embodiment the acidic aqueous solution has a pH of between about -1 and about 2. In one embodiment the acidic aqueous solution has a pH of between about 0 and about 2. In one embodiment the medium has a pH of between about -1 and about 2. In one embodiment the medium has a pH of between about 0 and about 2. In one embodiment, the acidic aqueous solution is an about 0.1 to 10 M solution of an acid. In embodiment, the acid is hydrochloric acid, hydrobromic acid, nitric acid, phosphoric acid, or sulfuric acid. In one embodiment, the acidic aqueous solution is an about 1 M solution of sulfuric acid (H2SO4).

[0100]

[0069] In one embodiment, the cathode and anode of the solar or electrochemical ammonia generator are connected to a voltage source capable of applying an overpotential. In one embodiment, the voltage source can be any voltage source known in the art, for example a photovoltaic voltage source, a battery, or another electronic device.

[0101]

[0070] In certain embodiments, provided herein is an electrochemical sensor comprising at least two electrodes and an electrolyte. In certain embodiments, one of the at least two electrodes comprises a mixed metal oxide described herein. In one embodiment, one of the at least two electrodes is an electrode described herein. In certain embodiments, one or more of the at least two electrodes are in contact with an an ion-permeable membrane. In certain embodiments, the electrolyte is impregnated into one or more of the at least two electrodes and / or the ion-permeable membrane.

[0102] NAI-5002876540vl 20 Attorney Docket No. 14722-013-228

[0103]

[0071] In certain embodiments, provided herein is an electrochemical capacitor comprising an anode, a cathode, and an electrolyte. In certain embodiments, the anode comprises a mixed metal oxide described herein. In one embodiment, the anode is an electrode described herein. In certain embodiments, the anode and the cathode are separated by an ion-permeable membrane. In certain embodiments, the electrolyte is impregnated into the pair of electrodes and / or the ion- permeable membrane.

[0104] 4.5 Methods of Use

[0105]

[0072] In certain embodiments, provided herein is a method of water oxidation comprising contacting an electrode or an electrolyzer described herein with an aqueous solution and applying an overpotential.

[0106]

[0073] In certain embodiments, provided herein is a method of oxygen evolution comprising contacting an electrode or an electrolyzer described herein with an aqueous solution and applying an overpotential.

[0107]

[0074] In one embodiment, the aqueous solution is acidic. In one embodiment, the aqueous solution has a pH of between about -1 and about 2. In one embodiment, the aqueous solution has a pH of between about 0 and about 2. In one embodiment, the aqueous solution is an about 0.1 to 10 M solution of an acid. In embodiment, the acid is hydrochloric acid, hydrobromic acid, nitric acid, phosphoric acid, or sulfuric acid. In one embodiment, the aqueous solution is an about 1 M H2SO4 solution.

[0108]

[0075] In one embodiment, the overpotential is less than 700 mV. In one embodiment, the overpotential is less than 600 mV. In one embodiment, the overpotential is less than 500 mV. In one embodiment, the overpotential is less than 400 mV. In one embodiment, the overpotential is between about 300 and about 700 mV. In one embodiment, the overpotential is between about 400 and about 700 mV. In one embodiment, the overpotential is between about 450 and about 650 mV.

[0109]

[0076] In one embodiment, continuously applying the overpotential results in water oxidation and / or oxygen evolution over a period of at least 30 minutes. In one embodiment, continuously applying the overpotential results in water oxidation and / or oxygen evolution over a period of at least 4 hours. In one embodiment, continuously applying the overpotential

[0110] NAI-5002876540vl 21 Atorney Docket No. 14722-013-228 maintains an geometric current density of at least 10 mA / cm2over a period of at least 30 minutes. In one embodiment, continuously applying the overpotential maintains an geometric current density of at least 10 mA / cm2over a period of at least 4 hours.

[0111]

[0077] In certain embodiments, also provided herein is a method of reducing and / or valorizing CO2 comprising: (a) oxidizing one or more protic compounds at a first electrode to release electrons, wherein the first electrode is an electrode described herein; and (b) reducing CO2 at a second electrode with the electrons released by oxidizing the one or more protic compounds at the first electrode. In one embodiment, the second electrode comprises a suitable reduction catalyst known in the art, including but are not limited to Cu, Ni, Pt, NiMo, and NiCo. In one embodiment, step b produces one or more hydrocarbon products.

[0112]

[0078] In certain embodiments, also provided herein is a method of reducing and / or valorizing CO comprising: (a) oxidizing one or more protic compounds at a first electrode to release electrons, wherein the first electrode is an electrode described herein; and (b) reducing CO at a second electrode with the electrons released by oxidizing the one or more protic compounds at the first electrode. In one embodiment, the second electrode comprises a suitable reduction catalyst known in the art, including but are not limited to Cu, Ni, Pt, NiMo, and NiCo. In one embodiment, step b produces one or more hydrocarbon products.

[0113]

[0079] In certain embodiments, also provided herein is a method of reducing N2 comprising: (a) oxidizing one or more protic compounds at a first electrode to release electrons, wherein the first electrode is an electrode described herein; and (b) reducing N2 at a second electrode with the electrons released by oxidizing the one or more protic compounds at the first electrode. In one embodiment, step b produces ammonia (NH3). In one embodiment, the second electrode comprises a suitable reduction catalyst known in the art, including but are not limited to Cu, Ni, Pt, NiMo, and NiCo.

[0114]

[0080] In certain embodiments, also provided herein is a method of producing NH3 comprising: (a) oxidizing one or more protic compounds at a first electrode to release electrons, wherein the first electrode is an electrode described herein; and (b) reducing N2 at a second electrode with the electrons released by oxidizing the one or more protic compounds at the first electrode. In one embodiment, the second electrode comprises a suitable reduction catalyst known in the art, including but are not limited to Cu, Ni, Pt, NiMo, and NiCo.

[0115] NAI-5002876540vl 22 Attorney Docket No. 14722-013-228

[0116]

[0081] In certain embodiments, also provided herein is a method of green hydrogen (H2) production comprising: (a) oxidizing one or more protic compounds at a first electrode to release electrons, wherein the first electrode is an electrode described herein; and (b) reducing protons (H+) or proton equivalents at a second electrode with the electrons released by oxidizing the one or more protic compounds at the first electrode. In one embodiment, the second electrode comprises a suitable reduction catalyst known in the art, including but are not limited to Cu, Ni, Pt, NiMo, and NiCo.

[0117]

[0082] In one embodiment, the one or more protic compounds is or comprises an amine. In one embodiment, the one or more protic compounds is or comprises an alcohol. In one embodiment, the one or more protic compounds is or comprises water.

[0118]

[0083] In one embodiment, oxidizing the one or more protic compounds at the first electrode in step a occurs in an acidic aqueous solution. In one embodiment, the aqueous solution has a pH which is between about 0 and about 2. In one embodiment, the aqueous solution has a pH which is between about -1 and about 2.

[0119]

[0084] In one embodiment, oxidizing the one or more protic compounds at the first electrode in step a occurs at an overpotential of less than 700 mV. In one embodiment, oxidizing the one or more protic compounds at the first electrode in step a occurs at an overpotential of less than 600 mV. In one embodiment, oxidizing the one or more protic compounds at the first electrode in step a occurs at an overpotential of less than 500 mV. In one embodiment, oxidizing the one or more protic compounds at the first electrode in step a occurs at an overpotential of less than 400 mV. In one embodiment, oxidizing the one or more protic compounds at the first electrode in step a occurs at an overpotential which is between about 300 and about 700 mV. In one embodiment, oxidizing the one or more protic compounds at the first electrode in step a occurs at an overpotential which is between about 400 and about 700 mV. In one embodiment, oxidizing the one or more protic compounds at the first electrode in step a occurs at an overpotential which is between about 450 and about 650 mV.

[0120]

[0085] In certain embodiments, also provided herein is a method of electrochemical synthesis comprising: (a) oxidizing a first reactant at a first electrode to release electrons, wherein the first electrode is an electrode described herein; and (b) reducing a second reactant at a second electrode with the electrons released by oxidizing the first reactant at the first electrode.

[0121] NAI-5002876540vl 23 Attorney Docket No. 14722-013-228

[0122] In one embodiment, the second electrode comprises a suitable reduction catalyst known in the art, including but are not limited to Cu, Ni, Pt, NiMo, and NiCo. In certain embodiments, the first reactant is an organic compound. In certain embodiments, the organic compound is an alkane, an alkene, or an alkyne. In other embodiments, the organic compound is an alcohol or an aldehyde. In certain embodiments, the second reactant is a proton (H+) or proton equivalent. In other embodiments, the second reactant is an unsaturated organic compound, for example, an alkene, an alkyne, an aldehyde, a ketone, an ester, an amide, or a carboxylic acid.

[0123]

[0086] In certain embodiments, also provided herein is a method of electrochemical sensing comprising (i) exposing an analyte to an electrochemical sensor described herein, and (ii) oxidizing or reducing the analyte in the electrochemical sensor. In certain embodiments, the electrochemical sensor comprises an mixed metal oxide or an electrode described herein.

[0124] 5. EXAMPLES

[0125]

[0087] As used herein, the symbols and conventions used in these processes, schemes and examples, regardless of whether a particular abbreviation is specifically defined, are consistent with those used in the contemporary scientific literature, for example, the Journal of the American Chemical Society. Specifically, but without limitation, the following abbreviations may be used in the examples and throughout the specification: g (grams); mg (milligrams); mL (milliliters); pL (microliters); M (molar); mM (millimolar); pM (micromolar); eq. (equivalent); mmol (millimoles); V (volt); A (ampere); mA (milliampere); h, hr or hrs (hour or hours); min (minutes); and MS (mass spectrometry).

[0126]

[0088] For all of the following examples, unless otherwise specified, standard work-up and purification methods known to those skilled in the art can be utilized. Unless otherwise specified, all temperatures are expressed in °C (degrees Centigrade). All reactions and manipulations were conducted at room temperature unless otherwise noted. Synthetic methodologies illustrated herein are intended to exemplify the applicable chemistry through the use of specific examples and are not indicative of the scope of the disclosure.

[0127] Example 1: Synthesis of Cobalt Bismuth Oxide Electrodes

[0128]

[0089] Synthesis of cobalt bismuth oxide electrodes was performed using gradient physical vapor deposition (PVD) to produce thin films of cobalt bismuth oxide on platinized silicon wafer

[0129] NAI-5002876540vl 24 Atorney Docket No. 14722-013-228 substrates. Optionally, as a second step the prepared thin fdms were annealed via heat treatment in a box furnace in air at temperatures of up to 600 °C for up to 5 hours.

[0130] Example 2: Characterization of Cobalt Bismuth Oxide Electrodes

[0131]

[0090] Elemental composition of cobalt bismuth oxide electrodes prepared as described in Example 1 was assessed via SEM / EDS (Scanning Electron Microscopy / Energy Dispersive Spectroscopy) in a PhenomXL G2 SEM manufactured by Nanoscience Instruments. EDS measurements were performed with an accelerating voltage of lOkV, and quantified using the analysis software provided by the manufacturer. The assessed cobalt content of the prepared films ranged from 15% to 91% of total metals on an atomic percentage basis. The mixed metal oxides have an atomic molar density on the order of 0.02 mol / cm2.

[0132]

[0091] The thickness of the cobalt bismuth oxide electrodes was assessed via XRF (X-ray fluorescence), using a P series XRF instrument manufactured by Bowman XRF. Measurements were performed for three minutes with a spot size of 0.6mm, and quantified using the analysis software provided by the manufacturer to calculate film thickness and composition. The thickness of the cobalt bismuth oxide catalyst films as assessed by XRF ranged from 45 to 75 nm.

[0133] Example 3: Oxygen Evolution in Acidic Medium

[0134]

[0092] Standard oxygen evolution tests were performed in flowing IM H2SO4 electrolyte with a continuous applied geometric current density of 10mA / cm2. During the oxygen evolution tests, the electrode potential of the catalyst was assessed using a leakfree silver-silver chloride reference electrode immersed in the same electrolyte solution.

[0135]

[0093] Depending on composition and annealing conditions, cobalt bismuth oxide electrodes catalyzed oxygen evolution with applied overpotentials ranging from 0.47 to 0.65 V. Results for certain exemplary cobalt bismuth oxide electrodes are shown below.

[0136] NAI-5002876540vl 25 Attorney Docket No. 14722-013-228

[0137]

[0094] The results demonstrate that cobalt bismuth oxide electrodes can successfully produce O2 with a stable overpotential which is lower than the Pt benchmark over a period of at least four hours of continuous operation at a geometric current density 10mA / cm2in a flowing IM H2SO4 electrolyte.

[0138]

[0095] The embodiments described above are intended to be merely exemplary, and 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, and procedures. All such equivalents are considered to be within the scope of the claimed subject matter and are encompassed by the appended claims.

[0139]

[0096] All of the patents, patent applications and publications referred to herein are incorporated herein in their entireties. Citation or identification of any reference in this application is not an admission that such reference is available as prior art to the claimed subject matter.

[0140] NAI-5002876540vl 26

Claims

Atorney Docket No. 14722-013-228CLAIMSWhat is claimed:

1. A mixed metal oxide comprising cobalt and bismuth in an atomic ratio of x (Co) to y (Bi), wherein x is greater than y.

2. The mixed metal oxide of claim 1, wherein x is between about 0.60 and about 0.95, and y is between about 0.05 and about 0.40.

3. The mixed metal oxide of claim 2, wherein x is between about 0.80 and about 0.95.

4. The mixed metal oxide of claim 3, wherein x is between about 0.85 and about 0.90.

5. The mixed metal oxide of claim 4, wherein x is about 0.85, about 0.86, about 0.87, about 0.88, about 0.89, or about 0.90.

6. The mixed metal oxide of any one of claims 2 to 5, wherein y is between about 0.05 and 0.20.

7. The mixed metal oxide of claim 6, wherein y is between about 0.10 and about 0.15.

8. The mixed metal oxide of claim 7, wherein y is about 0.10, about 0.11, about 0.12, about 0.13, about 0.14, or about 0.15.

9. The mixed metal oxide of claim 2, wherein x is between about 0.60 and about 0.70.

10. The mixed metal oxide of claim 9, wherein x is between about 0.63 and about 0.68.NAI-5002876540vl 27Atorney Docket No. 14722-013-22811 . The mixed metal oxide of claim 10, wherein x is about 0.63, about 0.64, about 0.65, about 0.66, about 0.67, or about 0.68.

12. The mixed metal oxide of any one of claims 2 and 9 to 11, wherein y is between about 0.30 and about 0.40.

13. The mixed metal oxide of claim 12, wherein y is between about 0.32 and about 0.37.

14. The mixed metal oxide of claim 13, wherein y is about 0.32, about 0.33, about 0.34, about 0.35, about 0.36, or about 0.37.

15. The mixed metal oxide of any one of claims 1 to 14, comprising oxygen in an atomic ratio of oxygen (O) to cobalt and bismuth (Co + Bi) which is between about 1 and about 1.5.

16. The mixed metal oxide of any one of claims 1 to 15, wherein the atomic ratio has been determined by Energy Dispersive Spectroscopy (EDS).

17. The mixed metal oxide of any one of claims 1 to 16, having an atomic molar density which is between about 0.002 mol / cm2and about 0.2 mol / cm2, optionally wherein the atomic molar density is the atomic molar density of Co, Bi, or O, or combinations thereof, in the mixed metal oxide.

18. The mixed metal oxide of claim 17, wherein the atomic molar density is between about 0.005 mol / cm2and about 0.1 mol / cm2.

19. The mixed metal oxide of claim 18, wherein the atomic molar density is between about 0.008 mol / cm2and about 0.08 mol / cm2.

20. An electrode comprising the mixed metal oxide of any one of claims 1 to 19.NAI-5002876540vl 28Atorney Docket No. 14722-013-22821 . The electrode of claim 20, wherein the electrode is an anode.

22. The electrode of any one of claims 20 to 21, wherein the electrode is capable of oxidizing a fuel to convert chemical energy to electrical energy.

23. The electrode of claim 22, wherein the fuel is H2, NH3, or a hydrocarbon.

24. The electrode of any one of claims 20 to 23, wherein the electrode is suitable for use as an electrode of an electrolyzer.

25. The electrode of any one of claims 20 to 24, wherein the electrode is an electrode of an electrolyzer.

26. The electrode of any one of claims 20 to 25, wherein the electrode is capable of oxidizing water at an applied potential.

27. The electrode of any one of claims 20 to 26, wherein the electrode is capable of evolving oxygen at an applied potential.

28. The electrode of any one of claims 20 to 27, wherein the electrode is capable of operating in an acidic solution.

29. The electrode of any one of claims 20 to 29, wherein the electrode is capable of operating in an acidic aqueous solution.

30. The electrode of claim 29, wherein the acidic aqueous solution has a pH of between about -1 and about 2.

31. The electrode of claim 29 or claim 30, wherein the acidic aqueous solution is an about 1 M solution of H2SO4.

32. The electrode of any one of claims 20 to 31 further comprising an electroactive substrate.NAI-5002876540vl 29Atorney Docket No. 14722-013-22833. The electrode of claim 32, wherein the electroactive substrate is a silicon-based substrate.

34. The electrode of claim 33, wherein the silicon-based substrate is a silicon wafer.

35. The electrode of claim 33 or claim 34, wherein the silicon-based substrate has a thickness which is between about 0.1 and about 10 mm.

36. The electrode of claim 35, wherein the thickness of the silicon-based substrate is between about 0.5 and about 1 mm.

37. The electrode of claim 36, wherein the thickness of the silicon-based substrate is between about 0.7 and about 0.8 mm.

38. The electrode of any one of claims 32 to 37, wherein the electroactive substrate comprises a layer of SiCh.

39. The electrode of claim 38, wherein the layer of SiCh has a thickness which is greater than 100 nm.

40. The electrode of claim 38 or claim 39, wherein the thickness of the SiCh layer is between about 100 nm and about 1 mm.41 . The electrode of any one of claims 38 to 40, wherein the thickness of the SiCh layer is between about 100 nm and about 800 nm.

42. The electrode of any one of claims 38 to 40, wherein the thickness of the SiCh layer is between about 100 nm and about 500 nm.

43. The electrode of any one of claims 32 to 42, wherein the electroactive substrate comprises a layer of titanium (Ti).NAI-5002876540vl 30Atorney Docket No. 14722-013-22844. The electrode of claim 43, wherein the layer of Ti has a thickness which is between about 1 nm and about 25 nm.

45. The electrode of claim 44, wherein the thickness of the Ti layer is between about 5 nm and about 15 nm.

46. The electrode of any one of claims 32 to 45, wherein the electroactive substrate comprises a layer of platinum (Pt).

47. The electrode of claim 46, wherein the layer of Pt has a thickness which is between about 10 nm and about 100 nm.

48. The electrode of claim 47, wherein the thickness of the layer of Pt is between about 40 and about 60 nm.

49. The electrode of any one of claims 32 to 48, comprising a layer of the mixed metal oxide having a thickness which is between about 10 nm and about 100 nm.

50. The electrode of claim 49, wherein the thickness of the layer of the mixed metal oxide is between about 40 nm and about 80 nm.

51. The electrode of any one of claims 32 to 50, wherein the electrode comprises, in order from top to bottom, a layer of the mixed metal oxide and the electroactive substrate, and optionally wherein the electrode does not comprise tin (Sn).

52. The electrode of any one of claims 32 to 50, wherein the electrode comprises, in order from top to bottom, a layer of the mixed metal oxide, a layer of Pt, a layer of Ti, a layer of SiCh, and a silicon wafer.

53. The electrode of claim 52, wherein: a. the layer of the mixed metal oxide has a thickness which is between about 10 nm and about 100 nm; and / orNAI-5002876540vl 31Attorney Docket No. 14722-013-228 b. the layer of Pt has a thickness which is between about 10 nm and about 100 nm; and / or c. the layer of Ti has a thickness which is between about 1 nm and about 25 nm; and / or d. the layer of SiCh has a thickness which is greater than 100 nm; and / or e. the silicon wafer has a thickness which is between about 0.1 and about 10 mm.

54. The electrode of claim 53, wherein: a. the thickness of the layer of the mixed metal oxide is between about 40 nm and about 80 nm; and / or b. the thickness of the layer of Pt is between about 40 and about 60 nm; and / or c. the thickness of the Ti layer is between about 5 nm and about 15 nm; and / or d. the thickness of the SiC>2 layer is between about 100 nm and about 1 mm; and / or e. the thickness of the silicon-based substrate is between about 0.5 and about 1 mm.

55. The electrode of claim 53, wherein: a. the thickness of the layer of the mixed metal oxide is between about 40 nm and about 80 nm; and / or b. the thickness of the layer of Pt is between about 40 and about 60 nm; and / or c. the thickness of the Ti layer is between about 5 nm and about 15 nm; and / or d. the thickness of the SiCh layer is between about 100 nm and about 1 mm; and / or e. the thickness of the silicon-based substrate is between about 0.7 and about 0.8 mm.NAI-5002876540vl 32Atorney Docket No. 14722-013-22856. The electrode of any one of claims 32 to 55 which has been prepared by depositing Co and Bi onto the electroactive substrate.

57. The electrode of claim 56, wherein the depositing comprises sputtering Co and Bi onto the electroactive substrate.

58. The electrode of claim 56 or 57, wherein the depositing comprises gradient physical vapor deposition (PVD) of Co and Bi onto the electroactive substrate.

59. The electrode of any one of claims 56 to 58, wherein the electrode has not been annealed via heat treatment after the depositing of Co and Bi onto the electroactive substrate.

60. The electrode of any one of claims 56 to 58, wherein the electrode has been annealed via heat treatment after the depositing of Co and Bi onto the electroactive substrate.

61. The electrode of claim 60, wherein the electrode has been annealed at a temperature which is between about 500 and about 600 °C, for a period which is between about 1 and about 5 hours, in a box furnace in air, after the depositing of Co and Bi onto the electroactive substrate.

62. The electrode of any one of claims 20 to 61, wherein the electrode is stable for at least 30 minutes in a solution having a pH of about 0, as determined by Oxygen Evolution Assay.

63. The electrode of any one of claims 20 to 62, wherein the electrode is stable for at least 4 hours in a solution having a pH of about 0, as determined by Oxygen Evolution Assay.

64. The electrode of any one of claims 20 to 63, wherein the electrode is stable for at least 30 minutes in a solution of about 1 M H2SO4, as determined by Oxygen Evolution Assay.

65. The electrode of any one of claims 20 to 64, wherein the electrode is stable for at least 4 hours in a solution of about 1 M H2SO4, as determined by Oxygen Evolution Assay.NAI-5002876540vl 33Atorney Docket No. 14722-013-22866. The electrode of any one of claims 20 to 65, wherein the electrode is stable for at least 30 minutes at a continuous applied geometric current density of about 10 mA / cm2, as determined by Oxygen Evolution Assay.

67. The electrode of any one of claims 20 to 66, wherein the electrode is stable for at least 4 hours at a continuous applied geometric current density of about 10 mA / cm2, as determined by Oxygen Evolution Assay.

68. The electrode of any one of claims 20 to 67, wherein the electrode is stable for at least 30 minutes in a solution having a pH of about 0, and at a continuous applied geometric current density of about 10 mA / cm2, as determined by Oxygen Evolution Assay.

69. The electrode of any one of claims 20 to 68, wherein the electrode is stable for at least 4 hours in a solution having a pH of about 0, and at a continuous applied geometric current density of about 10 mA / cm2, as determined by Oxygen Evolution Assay.

70. The electrode of any one of claims 20 to 69, wherein the electrode is stable for at least 30 minutes in a solution of about 1 M H2SO4 at a continuous applied geometric current density of about 10 mA / cm2, as determined by Oxygen Evolution Assay.

71. The electrode of any one of claims 20 to 70, wherein the electrode is stable for at least 4 hours in a solution of about 1 M H2SO4 at a continuous applied geometric current density of about 10 mA / cm2, as determined by Oxygen Evolution Assay.

72. The electrode of any one of claims 20 to 71, wherein the electrode has an overpotential for water oxidation and / or oxygen evolution of less than 700 mV.

73. The electrode of any one of claims 20 to 72, wherein the electrode has an overpotential for water oxidation and / or oxygen evolution of less than 600 mV.

74. The electrode of any one of claims 20 to 73, wherein the electrode has an overpotential for water oxidation and / or oxygen evolution of less than 500 mV.NAI-5002876540vl 34Atorney Docket No. 14722-013-22875. The electrode of any one of claims 20 to 74, wherein the electrode has an overpotential for water oxidation and / or oxygen evolution of less than 400 mV.

76. The electrode of any one of claims 20 to 75, wherein the electrode has an overpotential for water oxidation and / or oxygen evolution of between about 300 and about 700 mV.

77. The electrode of any one of claims 20 to 76, wherein the electrode has an overpotential for water oxidation and / or oxygen evolution of between about 400 and about 700 mV.

78. The electrode of any one of claims 20 to 77, wherein the electrode has an overpotential for water oxidation and / or oxygen evolution of between about 450 and about 650 mV.

79. The electrode of any one of claims 20 to 78, wherein the electrode maintains a continuous applied geometric current density of at least 10 mA / cm2for at least 30 minutes at an overpotential for evolution of oxygen of between about 300 and about 700 mV in a solution having a pH of 0.

80. The electrode of any one of claims 20 to 79, wherein the electrode maintains a continuous applied geometric current density of at least 10 mA / cm2for at least 4 hours at an overpotential for evolution of oxygen of between about 300 and about 700 mV in a solution having a pH of 0.

81. The electrode of any one of claims 20 to 80, wherein the electrode maintains a continuous applied geometric current density of at least 10 mA / cm2for at least 30 minutes at an overpotential for evolution of oxygen of between about 300 and about 700 mV in a solution of about 1 M H2SO4.

82. The electrode of any one of claims 20 to 81, wherein the electrode maintains a continuous applied geometric current density of at least 10 mA / cm2for at least 4 hours at anNAI-5002876540vl 35Atorney Docket No. 14722-013-228 overpotential for evolution of oxygen of between about 300 and about 700 mV in a solution of about 1 M H2SO4.

83. An electrolyzer comprising an anode and a cathode, wherein the anode is an electrode according to any one of claims 20 to 82.

84. A method of water oxidation comprising contacting the electrode of any one of claims 20 to 82, or an electrolyzer of claim 83, with an aqueous solution and applying an overpotential.

85. A method of oxygen evolution comprising contacting the electrode of any one of claims 20 to 82, or an electrolyzer of claim 83, with an aqueous solution and applying an overpotential.

86. The method of claim 84 or claim 85, wherein the aqueous solution is acidic.

87. The method of claim 86, wherein the aqueous solution has a pH of between about -1 and about 2.

88. The method of any one of claims 84 to 87, wherein the aqueous solution is an about 1 M H2SO4 solution.

89. The method of any one of claims 84 to 88, wherein the overpotential is less than 700 mV.

90. The method of any one of claims 84 to 89, wherein the overpotential is less than 600 mV.

91. The method of any one of claims 84 to 90, wherein the overpotential is less than 500 mV.NAI-5002876540vl 36Atorney Docket No. 14722-013-22892. The method of any one of claims 84 to 91 , wherein the overpotential is less than 400 mV.

93. The method of any one of claims 84 to 92, wherein the overpotential is between about 300 and about 700 mV.

94. The method of any one of claims 84 to 93, wherein the overpotential is between about 400 and about 700 mV.

95. The method of any one of claims 84 to 94, wherein the overpotential is between about 450 and about 650 mV.

96. The method of any one of claims 84 to 95, wherein continuously applying the overpotential results in water oxidation and / or oxygen evolution over a period of at least 30 minutes.

97. The method of any one of claims 84 to 96, wherein continuously applying the overpotential results in water oxidation and / or oxygen evolution over a period of at least 4 hours.

98. The method of any one of claims 84 to 97, wherein continuously applying the overpotential maintains an geometric current density of at least 10 mA / cm2over a period of at least 30 minutes.

99. The method of any one of claims 84 to 98, wherein continuously applying the overpotential maintains an geometric current density of at least 10 mA / cm2over a period of at least 4 hours.

100. A method of reducing and / or valorizing CO2 comprising: a. oxidizing one or more protic compounds at a first electrode to release electrons, wherein the first electrode is an electrode according to any one of claims 20 to 82; and b. reducing CO2 at a second electrode with the electrons released by oxidizing the one or more protic compounds at the first electrode.NAI-5002876540vl 37Attorney Docket No. 14722-013-228101. A method of reducing and / or valorizing CO comprising: a. oxidizing one or more protic compounds at a first electrode to release electrons, wherein the first electrode is an electrode according to any one of claims 20 to 82; and b. reducing CO at a second electrode with the electrons released by oxidizing the one or more protic compounds at the first electrode.

102. The method of claim 100 or claim 101, wherein step b produces one or more hydrocarbon products.

103. A method of reducing N2 comprising: a. oxidizing one or more protic compounds at a first electrode to release electrons, wherein the first electrode is an electrode according to any one of claims 20 to 82; and b. reducing N2 at a second electrode with the electrons released by oxidizing the one or more protic compounds at the first electrode.

104. The method of claim 103, wherein step b produces ammonia (NH3).

105. A method of producing NH3 comprising: a. oxidizing one or more protic compounds at a first electrode to release electrons, wherein the first electrode is an electrode according to any one of claims 20 to 82; and b. reducing N2 at a second electrode with the electrons released by oxidizing the one or more protic compounds at the first electrode.

106. A method of green hydrogen (H2) production comprising: a. oxidizing one or more protic compounds at a first electrode to release electrons, wherein the first electrode is an electrode according to any one of claims 20 to 82; and b. reducing protons (H+) or proton equivalents at a second electrode with the electrons released by oxidizing the one or more protic compounds at the first electrode.

107. The method of any one of claims 100 to 106, wherein the one or more protic compounds is or comprises water.NAI-5002876540vl 38Atorney Docket No. 14722-013-228108. The method of any one of claims 100 to 107, wherein oxidizing the one or more protic compounds at the first electrode in step a occurs in an acidic aqueous solution.

109. The method of claim 108, wherein the acidic aqueous solution has a pH which is between about -1 and about 2.

110. The method of any one of claims 100 to 109, wherein oxidizing the one or more protic compounds at the first electrode in step a occurs at an overpotential of less than 700 mV.

111. The method of any one of claims 100 to 110, wherein oxidizing the one or more protic compounds at the first electrode in step a occurs at an overpotential of less than 600 mV.

112. The method of any one of claims 100 to 111, wherein oxidizing the one or more protic compounds at the first electrode in step a occurs at an overpotential of less than 500 mV.

113. The method of any one of claims 100 to 112, wherein oxidizing the one or more protic compounds at the first electrode in step a occurs at an overpotential of less than 400 mV.

114. The method of any one of claims 100 to 113, wherein oxidizing the one or more protic compounds at the first electrode in step a occurs at an overpotential which is between about 300 and about 700 mV.

115. The method of any one of claims 100 to 114, wherein oxidizing the one or more protic compounds at the first electrode in step a occurs at an overpotential which is between about 400 and about 700 mV.

116. The method of any one of claims 100 to 115, wherein oxidizing the one or more protic compounds at the first electrode in step a occurs at an overpotential which is between about 450 and about 650 mV.

117. A method of preparing the mixed metal oxide of any one of claims 1 to 19, or the electrode of any one of claims 20 to 82, comprising depositing Co and Bi onto a substrate.NAI-5002876540vl 39Atorney Docket No. 14722-013-228118. The method of claim 117, wherein the depositing comprises sputtering Co and Bi onto the substrate.

119. The method of claim 117 or 118, wherein the depositing comprises physical vapor deposition (PVD) or chemical vapor deposition (CVD) of Co and Bi onto the substrate, optionally wherein the depositing comprises gradient physical vapor deposition (PVD) of Co and Bi onto the substrate.

120. The method of any one of claims 117 to 119, wherein the method does not comprise annealing the mixed metal oxide via heat treatment after the depositing step.

121. The method of any one of claims 117 to 119, wherein the method comprises annealing the mixed metal oxide via heat treatment after the depositing step.

122. The method of claim 121, wherein annealing is conducted at a temperature which is between about 500 and about 600 °C, for a period which is between about 1 and about 5 hours, in a box furnace in air.

123. The method of any one of claims 117 to 122, which results in a layer of the mixed metal oxide having a thickness which is between about 10 nm and about 100 nm.

124. The method of claim 123, which results in a layer of the mixed metal oxide having a thickness which is between about 40 nm and about 80 nm.

125. The method of any one of claims 117 to 124, wherein the substrate is an electroactive substrate.

126. The method of any one of claims 117 to 125, wherein the substrate comprises a layer of silicon.

127. The method of claim 126, wherein the layer of silicon is a silicon wafer.NAI-5002876540vl 40Atorney Docket No. 14722-013-228128. The method of claim 126 or claim 127, wherein the layer of silicon has a thickness which is between about 0.1 and about 10 mm.

129. The method of claim 128, wherein the thickness of the layer of silicon is between about 0.5 and about 1 mm.

130. The method of claim 129, wherein the thickness of the layer of silicon is between about 0.7 and about 0.8 mm.

131. The method of any one of claims 117 to 130, wherein the substrate comprises a layer of SiCh.

132. The method of claim 131, wherein the layer of SiCh has a thickness which is greater than 100 nm.

133. The method of claim 132, wherein the thickness of the SiCh layer is between about 100 nm and about 1 mm.

134. The method of claim 133, wherein the thickness of the SiCh layer is between about 100 nm and about 800 nm.

135. The method of claim 134, wherein the thickness of the SiCh layer is between about 100 nm and about 500 nm.

136. The method of any one of claims 117 to 135, wherein the substrate comprises a layer of titanium (Ti).

137. The method of claim 136, wherein the layer of Ti has a thickness which is between about 1 nm and about 25 nm.

138. The method of claim 137, wherein the thickness of the Ti layer is between about 5 nm and about 15 nm.NAI-5002876540vl 41Atorney Docket No. 14722-013-228139. The method of any one of claims 117 to 138, wherein the substrate comprises a layer of platinum (Pt).

140. The method of claim 139, wherein the layer of Pt has a thickness which is between about 10 nm and about 100 nm.

141. The method of claim 140, wherein the thickness of the layer of Pt is between about 40 and about 60 nm.

142. The method of any one of claims 117 to 141, wherein the substrate comprises, in order from top to bottom, a layer of Pt, a layer of Ti, a layer of SiCh, and a silicon wafer.

143. The method of claim 142, wherein: a. the layer of Pt has a thickness which is between about 10 nm and about 100 nm; and / or b. the layer of Ti has a thickness which is between about 1 nm and about 25 nm; and / or c. the layer of SiCh has a thickness which is greater than 100 nm; and / or d. the silicon wafer has a thickness which is between about 0.1 and about 10 mm.

144. The method of claim 143, wherein: a. the thickness of the layer of Pt is between about 40 and about 60 nm; and / or b. the thickness of the Ti layer is between about 5 nm and about 15 nm; and / or c. the thickness of the SiCh layer is between about 100 nm and about 1 mm; and / or d. the thickness of the silicon-based substrate is between about 0.5 and about 1 mm.

145. The method of claim 143, wherein:NAI-5002876540vl 42Attorney Docket No. 14722-013-228 a. the thickness of the layer of Pt is between about 40 and about 60 nm; and / or b. the thickness of the Ti layer is between about 5 nm and about 15 nm; and / or c. the thickness of the SiCh layer is between about 100 nm and about 1 mm; and / or d. the thickness of the silicon-based substrate is between about 0.7 and about 0.8 mm.

146. The method of any one of claims 123 to 145, which results in the layer of the mixed metal oxide being deposited on top of the substrate.

147. An electrode which has been prepared according to the method of any one of claims 117 to 146.

148. The mixed metal oxide of any one of claims 1 to 19, wherein the mixed metal oxide is stable at low pH.

149. The electrode of any one of claims 1 to 82, wherein the electrode (i) is stable at low pH and / or (ii) has an overpotential for water oxidation and / or oxygen evolution which is between about 300 and about 700 mV in a solution having a pH of about 0.

150. An electrochemical sensor comprising at least two electrodes and an electrolyte, wherein one of the at least two electrodes is an electrode according to any one of claims 1 to 82.

151. An electrochemical capacitor comprising an anode, a cathode, and an electrolyte, wherein the anode is an electrode according to any one of claims 1 to 82.

152. A method of electrochemical synthesis comprising: (a) oxidizing a first reactant at a first electrode to release electrons, wherein the first electrode is an electrode according to any one of claims 1 to 82; and (b) reducing a second reactant at a second electrode with the electrons released by oxidizing the first reactant at the first electrode.NAI-5002876540vl 43Atorney Docket No. 14722-013-228153. A method of electrochemical sensing comprising (i) exposing an analyte to an electrochemical sensor according to claim 150, and (ii) oxidizing or reducing the analyte in the electrochemical sensor.NAI-5002876540vl 44

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