ELECTROCHEMICAL SYSTEM AND METHOD OF USING AN ELECTROCHEMICAL CELL

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority to U.S. Provisional Patent Application Serial No. 63/381,686 filed Oct. 31, 2022, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND

[0002] Hydrogen is a critical element in the production of various industrial chemicals, such as ammonia. Most hydrogen is currently produced through steam methane reforming, which also generates large amounts of greenhouse gases. The production of hydrogen through water electrolysis, which generates hydrogen and oxygen gas from water, is a desirable alternative that does not emit harmful byproducts. As water electrolysis technology continues to increase in scale and achieve higher current densities, the risk of undesirable side reactions increases, such as the production of hydrogen peroxide and ozone.

SUMMARY OF THE INVENTION

[0003] Various aspects of the present invention provide a method of using an electrochemical cell. The method includes sparging a gas including oxygen into an anolyte using an anolyte oxygen sparger, wherein the anolyte is circulated to contact an anode of an electrochemical cell including the anode, a cathode, and a membrane between the anode and the cathode.

[0004] Various aspects of the present invention provide an electrochemical system including an electrochemical cell. The electrochemical cell includes an anode, a cathode, and a membrane between the anode and the cathode. The system also includes an anolyte oxygen sparger than sparges a gas including oxygen into an anolyte that is circulated to contact the anode.

[0005] Various aspects of the present method and system can have advantages over other methods and systems for water electrolysis. For example, in various aspects, the sparging of the gas including oxygen into the anolyte in the methods and systems of the present invention can improve electrochemical performance, reduce overpotential, suppress undesired side-reactions, or a combination thereof. In various aspects, the sparging of the gas including oxygen into the anolyte in the methods and systems of the present invention can create two phase flow of liquid anolyte and a gas phase of entrained and/or headspace gas, which creates more convection and turbulence in the anolyte liquid, which can more quickly dislodge oxygen bubbles from the surface of the anode. In various aspects, the sparging of the gas including oxygen into the anolyte in the methods and systems of the present invention can increase the reaction rate of the water electrolysis and/or can decrease the amount of voltage that needs to be applied across the anode and cathode to achieve a particular rate or amount of water electrolysis. In various aspects, the sparging of the gas including oxygen into the anolyte in the methods and system of the present invention can prevent or dilute any hydrogen present in the gas phase of the anolyte (e.g., from crossover originating from the cathode-side of the membrane such as during low current density operation of the electrochemical cell) from forming an explosive composition in the gas phase.

BRIEF DESCRIPTION OF THE FIGURES

[0006] The drawings illustrate generally, by way of example, but not by way of limitation, various aspects of the present invention.

[0007] FIG. 1 illustrates an electrochemical system, in accordance with various aspects.

[0008] FIG. 2 illustrates an electrochemical system, in accordance with various aspects.

[0009] FIG. 3 illustrates an electrochemical system, in accordance with various aspects.

[0010] FIG. 4A illustrates a polarization curve for a non-platinum group metal (PGM) electrode without any gas sparging, in accordance with various aspects.

[0011] FIG. 4B illustrates a polarization curve for a PGM electrode without any gas sparging, in accordance with various aspects.

[0012] FIG. 4C illustrates a polarization curve for a non-platinum group metal (PGM) electrode with oxygen sparging, in accordance with various aspects. [0013] FIG. 4D illustrates a polarization curve for a PGM electrode with oxygen sparging, in accordance with various aspects.

[0014] FIG. 4E illustrates a polarization curve for a non-platinum group metal (PGM) electrode with nitrogen sparging the electrolyte, in accordance with various aspects.

[0015] FIG. 4F illustrates a polarization curve for a PGM electrode with nitrogen sparging the electrolyte, in accordance with various aspects.

[0016] FIG. 5 illustrates overpotential versus Tafel slope for a nonplatinum group metal (PGM) electrode without any gas sparging, sparging with oxygen gas, and sparging with nitrogen gas, in accordance with various aspects. [0017] FIG. 6 illustrates overpotential versus Tafel slope a platinum group metal (PGM) electrode without any gas sparging, sparging with oxygen gas, and sparging with nitrogen gas.

DETAILED DESCRIPTION OF THE INVENTION

[0018] Reference will now be made in detail to certain aspects of the disclosed subject matter. While the disclosed subject matter will be described in conjunction with the enumerated claims, it will be understood that the exemplified subject matter is not intended to limit the claims to the disclosed subject matter.

[0019] Throughout this document, values expressed in a range format should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a range of “about 0.1% to about 5%” or “about 0.1% to 5%” should be interpreted to include not just about 0.1% to about 5%, but also the individual values (e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.1% to 0.5%, 1.1% to 2.2%, 3.3% to 4.4%) within the indicated range. The statement “about X to Y” has the same meaning as “about X to about Y,” unless indicated otherwise. Likewise, the statement “about X, Y, or about Z” has the same meaning as “about X, about Y, or about Z,” unless indicated otherwise.

[0020] In this document, the terms “a,” “an,” or “the” are used to include one or more than one unless the context clearly dictates otherwise. The term “or” is used to refer to a nonexclusive “or” unless otherwise indicated. The statement “at least one of A and B” or “at least one of A or B” has the same meaning as “A, B, or A and B.” In addition, it is to be understood that the phraseology or terminology employed herein, and not otherwise defined, is for the purpose of description only and not of limitation. Any use of section headings is intended to aid reading of the document and is not to be interpreted as limiting; information that is relevant to a section heading may occur within or outside of that particular section.

[0021] In the methods described herein, the acts can be carried out in a specific order as recited herein. Alternatively, in any aspect(s) disclosed herein, specific acts may be carried out in any order without departing from the principles of the invention, except when a temporal or operational sequence is explicitly recited. Furthermore, specified acts can be carried out concurrently unless explicit claim language recites that they be carried out separately or the plain meaning of the claims would require it. For example, a claimed act of doing X and a claimed act of doing Y can be conducted simultaneously within a single operation, and the resulting process will fall within the literal scope of the claimed process.

[0022] The term “about” as used herein can allow for a degree of variability in a value or range, for example, within 10%, within 5%, or within 1% of a stated value or of a stated limit of a range, and includes the exact stated value or range.

[0023] The term “substantially” as used herein refers to a majority of, or mostly, as in at least about 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5%, 99.9%, 99.99%, or at least about 99.999% or more, or 100%. The term “substantially free of’ as used herein can mean having none or having a trivial amount of, such that the amount of material present does not affect the material properties of the composition including the material, such that about 0 wt% to about 5 wt% of the composition is the material, or about 0 wt% to about 1 wt%, or about 5 wt% or less, or less than, equal to, or greater than about 4.5 wt%, 4, 3.5, 3, 2.5, 2, 1.5, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.01, or about 0.001 wt% or less, or about 0 wt%.

Electrochemical system. [0024] The present invention pertains to a low energy electrochemical system and method of producing hydrogen and oxygen gas in an electrochemical cell. Disclosed herein are methods to increase the concentration of oxygen in the electrolyte solution electrochemical cell, or to saturate the electrolyte solution with oxygen. In one aspect the method includes using oxygen gas byproduct generated within the electrochemical cell to sparge the electrolyte with oxygen. In another aspect the method includes of using external oxygen sources to sparge the electrolyte. The increase in oxygen concentration or oxygen saturation of the electrolyte is achieved by introducing oxygen gas into the electrochemical system, e.g., oxygen sparging of the electrolyte within a holding tank. The methods of increasing the concentration of oxygen in the electrolyte or saturating the electrolyte with oxygen results in improved electrochemical performance, e.g., reduced overpotentials, and improved selectivity (e.g., suppressing undesirable side reactions). The oxygen-sparged electrolyte continues to favor the formation of oxygen gas, e.g., 2OH" H2O + V2O2 + 2e" at higher cell voltages, while an unsparged electrolyte more easily converts from oxygen evolution to formation of hydrogen peroxide, e.g., 2OH" H2O2 + 2e". The presently disclosed methods can be beneficial for systems using platinum group metal (PGM) electrodes, e.g., platinum, ruthenium, iridium, and nonplatinum group metal electrodes, e.g., nickel, cobalt, iron, copper, manganese, molybdenum. The electrodes may be as individual element, alloyed, or in an oxide form.

[0025] FIGS. 1-3 are illustrations of various aspects of the system. FIG. 1 illustrates an electrochemical system including an electrochemical cell including a cathode side 110 that includes a cathode, an anode side 130 that includes an anode, and a membrane 120 between the anode and cathode. The anode produces oxygen gas that is circulated with the anolyte back to recontact the anode via anolyte circulation loop 160. Outside of the electrochemical cell, the system sparges gas including oxygen into the anolyte. The sparger is not shown in FIG. 1 and can occur within circulation loop 160. The gas sparged into the anolyte can be headspace gas or entrained gas in the anolyte, added oxygen- containing gas, or a combination thereof. In various aspects, a separator can be included in the circulation loop 160 that separates the gas phase from the anolyte for sparging of the gas phase back into the anolyte, storage of a portion of the gas phase, or a combination thereof. The electrochemical system includes a hydrogen storage vessel 150 for storage of hydrogen generated by the cathode in cathode side 110 via flowline 140.

[0026] FIG. 2 illustrates an electrochemical system including an electrochemical cell including a cathode side 210 that includes a cathode, an anode side 230 that includes an anode, and a membrane 220 between the anode and cathode. The anode produces oxygen gas that is circulated with the anolyte back to recontact the anode via anolyte circulation loop 260. The anolyte circulation loop includes anolyte tank 265 for storing anolyte. Outside of the electrochemical cell, the system sparges gas including oxygen into the anolyte, such as in the anolyte tank, or such as in another location of the anolyte circulation loop. The sparger is not shown in FIG. 2. The gas sparged into the anolyte can be headspace gas or entrained gas in the anolyte, added oxygencontaining gas, or a combination thereof. In various aspects, a separator can be included in the circulation loop 260 that separates the gas phase from the anolyte for sparging of the gas phase back into the anolyte, storage of a portion of the gas phase, or a combination thereof. The electrochemical system includes a hydrogen storage vessel 250 for storage of hydrogen generated by the cathode in cathode side 210 via flowline 240.

[0027] FIG. 3 illustrates an electrochemical system including an electrochemical cell including a cathode side 310 that includes a cathode, an anode side 330 that includes an anode, and a membrane 320 between the anode and cathode. The anode produces oxygen gas that is circulated with the anolyte back to recontact the anode via anolyte circulation loop 360. Outside of the electrochemical cell, the system sparges gas including oxygen into the anolyte, such as in the circulation loop 360. The sparger is not shown in FIG. 3. The gas sparged into the anolyte can be headspace gas or entrained gas in the anolyte, added oxygen-containing gas, or a combination thereof. In various aspects, a separator can be included in the recirculation loop 360 that separates the gas phase from the anolyte for sparging of the gas phase back into the anolyte, storage of a portion of the gas phase, or a combination thereof. The electrochemical system includes a hydrogen storage vessel 350 for storage of hydrogen generated by the cathode in cathode side 310 via flowline 340. The electrochemical system includes an electrolyte tank that supplies electrolyte (i.e., anolyte and catholyte) via flow lines 380 to the cathode side 310 and the anode side 330 of the electrochemical cell.

[0028] Various aspects of the present invention provide an electrochemical system including an electrochemical cell. The electrochemical cell includes an anode, a cathode, and a membrane between the anode and the cathode. The system can also include an anolyte oxygen sparger than sparges a gas including oxygen into an anolyte that is circulated to contact the anode. The membrane can be any suitable membrane; for example, the membrane can be an ion exchange membrane (e.g., a cation exchange membrane or an anion exchange membrane), a micro-porous membrane, a nano-porous membrane, or a combination thereof. During use for electrolysis of water, the cathode of the electrochemical cell can generate hydrogen and the anode of the electrochemical cell can generate oxygen.

[0029] The anode can include a platinum group metal (PGM). The anode can include platinum, ruthenium, iridium, or a combination thereof.

[0030] The anode can include a non-platinum group metal. The anode can include nickel, cobalt, iron, copper, manganese, molybdenum, or a combination thereof.

[0031] The anode can be or include an individual element, an alloy, or an oxide.

[0032] The anolyte can be an aqueous liquid having any suitable temperature. For example, the anolyte can be an aqueous sodium hydroxide and/or potassium hydroxide solution having a temperature of 30 °C to 150 °C, or 40 °C to 140 °C, or less than or equal to 150 °C and greater than or equal to 30 °C and less than, equal to, or greater than 35°C, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, or 145 °C.

[0033] The gas including oxygen can have any suitable concentration of oxygen, such as a concentration of oxygen that is greater than ambient levels, such as a concentration of 22% to 100%, or 30% to 95%, or less than or equal to 100% and greater than or equal to 22% and greater than, equal to, or less than 23%, 24, 25, 26, 28, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 92, 94, 96, 97, 98, or 99%. In addition to the oxygen, the gas including oxygen can include any suitable additional one or more gases, such as one or more inert gases. For example, the gas including oxygen can further include nitrogen, argon, air, or a combination thereof. The oxygen in the gas including oxygen can include oxygen generated by the anode (e.g., during a previous cycle of contacting the anolyte with the anode), oxygen from an external source such as a storage tank or supply line, or a combination thereof.

[0034] The sparging includes releasing bubbles of the gas including oxygen into the anolyte. The sparging is in addition to the generation and release of oxygen by the anode during the electrolysis of water. The bubbles can be released from a pipe, a tube, a mesh, a sieve, a plate, a nozzle, a porous nozzle, a porous surface, or a combination thereof. The sparging can be performed outside of the electrochemical cell, such as in an anolyte circulation loop or component thereof (e.g., in an anolyte storage tank in the loop or fluidly connected to the loop). The sparger can sparge the gas including oxygen into the anolyte at any suitable rate, such as a rate of 0.01 mL to 100 mL of the gas per 1 mL of anolyte, 0.1 mL to 2 mL per 1 mL of anolyte, or less than or equal to 100 mL and greater than or equal to 0.01 mL and greater than, less than, or equal to 0.1 mL of the gas per 1 mL of anolyte, 0.2, 0.4, 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 8, 10, 15, 20, 25, 30, 35, 40, 50, 60, 70, 80, or 90 mL of the gas per 1 mL of anolyte. The sparging of the gas including oxygen into the anolyte can result in a dissolved concentration of oxygen in the anolyte (e.g., immediately after sparging, or at the time the anolyte re-enters the electrochemical cell, or a combination thereof) of 10 mg/L to 200 mg/L, or 20 mg/L to 100 mg/L.

[0035] The circulating of the anolyte to contact the anode can further include circulating a gas phase to contact the anode, wherein the gas phase is circulated to contact the anode with the anolyte. The anolyte and the gas phase can be circulated together, wherein with respect to the anolyte the gas phase can be a headspace gas, entrained gas (e.g., bubbles), or a combination thereof. The gas phase can have any suitable concentration of oxygen, such as a concentration of oxygen of 22% to 100%, or 30% to 95%, or less than or equal to 100% and greater than or equal to 22% and greater than, equal to, or less than 23%, 24, 25, 26, 28, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 92, 94, 96, 97, 98, or 99%. In various aspects, the gas phase is substantially free of hydrogen, or has a concentration of hydrogen with respect to oxygen in the gas phase of less than 5%, less than 4%, less than 3%, less than 2%, or less than 1%. By maintaining a low concentration of hydrogen with respect to oxygen, the system can avoid formation of an explosive mixture of hydrogen and oxygen.

[0036] The system can include an anolyte circulation loop that circulates the anolyte and the gas phase. The anolyte circulation loop can circulate anolyte and gas phase that previously contacted the anode out of the electrochemical cell, subject the anolyte to the sparging, and then circulate the sparged anolyte back into the electrochemical cell. The anolyte circulation loop can have any suitable volume ratio of the anolyte to the gas phase, such as 0.0001 : 1 to 10000: 1, 1 : 1 to 100: 1, or less than or equal to 10000: 1 and greater than or equal to 0.0001 : 1 and less than, equal to, or greater than 0.001 : 1, 0.01 : 1, 0.1 :1, 0.2:1, 0.4:1, 0.6: 1, 0.8:1, 1 :1, 1.2:1, 1.4: 1, 1.6:1, 1.8: 1, 2: 1, 3:1, 4:1, 6:1, 8:1, 10:1, 20: 1, 50: 1, 100: 1, 1000: 1, or 5000: 1.

[0037] The anolyte circulation loop can further include a separator that separates at least a portion of the gas phase from the combined anolyte and gas phase. The separator can be any suitable gas-liquid separator. A volume ratio of the portion of the gas phase separated from the gas phase to be circulated to contact the anode can be 0.0001 : 1 to 10000: 1, or less than or equal to 10000: 1 and greater than or equal to 0.0001 : 1 and less than, equal to, or greater than 0.001 :1, 0.01 : 1, 0.1 : 1, 0.2: 1, 0.4: 1, 0.6: 1, 0.8: 1, 1 :1, 1.2: 1, 1.4: 1, 1.6: 1, 1.8: 1, 2: 1, 3: 1, 4: 1, 6: 1, 8: 1, 10:1, 20: 1, 50: 1, 100: 1, 1000: 1, or 5000: 1.

[0038] The anolyte circulation loop can include one or more units in the circulation loop or fluidly connected to the circulation loop, such as an anolyte storage tank for storing anolyte, an oxygen storage tank (e.g., for storing the portion of the gas phase separated from the gas phase to be circulated to contact the anode), an electrolyte tank for supplying the anolyte (and optionally for supplying a catholyte), or a combination thereof. The electrolyte tank can contain an aqueous sodium hydroxide and/or potassium hydroxide solution. In various aspects, the system can further include a hydrogen storage tank for collecting hydrogen gas released from the cathode.

Method of using an electrochemical cell.

[0039] Various aspects of the present invention provide a method of using an electrochemical cell. The method includes sparging a gas including oxygen into an anolyte using an anolyte oxygen sparger, wherein the anolyte is circulated to contact an anode of an electrochemical cell including the anode, a cathode, and a membrane between the anode and the cathode. The membrane can be any suitable membrane; for example, the membrane can be an ion exchange membrane (e.g., a cation exchange membrane or an anion exchange membrane), a micro-porous membrane, a nano-porous membrane, or a combination thereof.

[0040] The anode can include a platinum group metal (PGM). The anode can include platinum, ruthenium, iridium, or a combination thereof.

[0041] The anode can include a non-platinum group metal. The anode can include nickel, cobalt, iron, copper, manganese, molybdenum, or a combination thereof.

[0042] The anode can be or include an individual element, an alloy, or an oxide.

[0043] The anolyte can be an aqueous liquid having any suitable temperature. For example, the anolyte can be an aqueous sodium hydroxide and/or potassium hydroxide solution having a temperature of 30 °C to 150 °C, or 40 °C to 140 °C, or less than or equal to 150 °C and greater than or equal to 30 °C and less than, equal to, or greater than 35°C, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, or 145 °C.

[0044] The gas that is sparged into the anolyte can further include an inert gas and/or nitrogen. The gas that is sparged into the anolyte can have any suitable concentration of oxygen gas. The method can include sparging the anolyte within a holding tank. The sparging of the gas including oxygen into the anolyte can improve electrochemical performance, reduces overpotential, suppresses undesired side-reactions, or a combination thereof. The sparging of the gas including oxygen into the anolyte can saturate the anolyte with oxygen. [0045] The anode can include a platinum group metal (PGM). The anode can include platinum, ruthenium, iridium, or a combination thereof.

[0046] The anode can include a non-platinum group metal. The anode can include nickel, cobalt, iron, copper, manganese, molybdenum, or a combination thereof.

[0047] The anode can be or include an individual element, an alloy, or an oxide. [0048] The gas including oxygen can have any suitable concentration of oxygen, such as a concentration of oxygen that is greater than ambient levels, such as a concentration of 22% to 100%, or 30% to 95%, or less than or equal to 100% and greater than or equal to 22% and greater than, equal to, or less than 23%, 24, 25, 26, 28, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 92, 94, 96, 97, 98, or 99%. In addition to the oxygen, the gas including oxygen can include any suitable additional one or more gases, such as one or more inert gases. For example, the gas including oxygen can further include nitrogen, argon, air, or a combination thereof. The oxygen in the gas including oxygen can include oxygen generated by the anode (e.g., during a previous cycle of contacting the anolyte with the anode), oxygen from an external source such as a storage tank or supply line, or a combination thereof.

[0049] The sparging includes releasing bubbles of the gas including oxygen into the anolyte. The sparging is in addition to the generation and release of oxygen by the anode during the electrolysis of water. The bubbles can be released from a pipe, a tube, a mesh, a sieve, a plate, a nozzle, a porous nozzle, a porous surface, or a combination thereof. The sparging can be performed outside of the electrochemical cell, such as in an anolyte circulation loop or component thereof (e.g., in an anolyte storage tank in the loop or fluidly connected to the loop). The sparger can sparge the gas including oxygen into the anolyte at any suitable rate, such as a rate of 0.01 mL to 100 mL of the gas per 1 mL of anolyte, 0.1 mL to 2 mL per 1 mL of anolyte, or less than or equal to 100 mL and greater than or equal to 0.01 mL and greater than, less than, or equal to 0.1 mL of the gas per 1 mL of anolyte, 0.2, 0.4, 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 8, 10, 15, 20, 25, 30, 35, 40, 50, 60, 70, 80, or 90 mL of the gas per 1 mL of anolyte. The sparging of the gas including oxygen into the anolyte can result in a dissolved concentration of oxygen in the anolyte (e.g., immediately after sparging, or at the time the anolyte re-enters the electrochemical cell, or a combination thereof) of 10 mg/L to 200 mg/L, or 20 mg/L to 100 mg/L.

[0050] The circulating of the anolyte to contact the anode can further include circulating a gas phase to contact the anode, wherein the gas phase is circulated to contact the anode with the anolyte. The anolyte and the gas phase can be circulated together, wherein with respect to the anolyte the gas phase can be a headspace gas, entrained gas (e.g., bubbles), or a combination thereof. The gas phase can have any suitable concentration of oxygen, such as a concentration of oxygen of 22% to 100%, or 30% to 95%, or less than or equal to 100% and greater than or equal to 22% and greater than, equal to, or less than 23%, 24, 25, 26, 28, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 92, 94, 96, 97, 98, or 99%. In various aspects, the gas phase is substantially free of hydrogen, or has a concentration of hydrogen with respect to oxygen in the gas phase of less than 5%, less than 4%, less than 3%, less than 2%, or less than 1%. By maintaining a low concentration of hydrogen with respect to oxygen, the method can avoid formation of an explosive mixture of hydrogen and oxygen.

[0051] The method can include circulating the anolyte and the gas phase in an anolyte circulation loop. The anolyte circulation loop can circulate anolyte and gas phase that previously contacted the anode out of the electrochemical cell, subject the anolyte to the sparging, and then circulate the sparged anolyte back into the electrochemical cell. The anolyte circulation loop can have any suitable volume ratio of the anolyte to the gas phase, such as 0.0001 : 1 to 10000: 1, 1 : 1 to 100: 1, or less than or equal to 10000: 1 and greater than or equal to 0.0001 : 1 and less than, equal to, or greater than 0.001 : 1, 0.01 : 1, 0.1 : 1, 0.2: 1, 0.4: 1, 0.6: 1, 0.8: 1, 1 : 1, 1.2: 1, 1.4: 1, 1.6: 1, 1.8: 1, 2:1, 3: 1, 4: 1, 6: 1, 8: 1, 10: 1, 20: 1, 50: 1, 100: 1, 1000: 1, or 5000: 1.

[0052] The method can further include separating at least a portion of the gas phase from the combined anolyte and gas phase in the anolyte circulation loop. The separation can be performed with any suitable gas-liquid separator. A volume ratio of the portion of the gas phase separated from the gas phase to be circulated to contact the anode can be 0.0001 : 1 to 10000: 1, or less than or equal to 10000: 1 and greater than or equal to 0.0001 : 1 and less than, equal to, or greater than 0.001 : 1, 0.01 : 1, 0.1 : 1, 0.2: 1, 0.4: 1, 0.6: 1, 0.8: 1, 1 : 1, 1.2: 1, 1.4:1, 1.6: 1, 1.8: 1, 2: 1, 3: 1, 4: 1, 6: 1, 8: 1, 10: 1, 20: 1, 50: 1, 100: 1, 1000: 1, or 5000: 1.

[0053] The method can include storing anolyte in an anolyte storage tank that is in the anolyte circulation loop or fluidly connected to the loop. The method can include storing the portion of the gas phase separated from the gas phase to be circulated to contact the anode in an oxygen storage tank that is in the anolyte circulation loop or fluidly connected to the loop. The method can include supplying the anolyte to the anolyte circulation loop from an electrolyte storage tank that is fluidly connected to the anolyte circulation loop. The method can include supplying catholyte to contact the cathode, such as from the electrolyte storage tank. The method can include collecting hydrogen gas released from the cathode. The method can include The anolyte circulation loop can include one or more units in the circulation loop or fluidly connected to the circulation loop, such as an anolyte storage tank for storing anolyte, an oxygen storage tank (e.g., for storing the portion of the gas phase separated from the gas phase to be circulated to contact the anode), an electrolyte tank for supplying the anolyte (and optionally for supplying a catholyte), or a combination thereof. The electrolyte tank can contain an aqueous sodium hydroxide and/or potassium hydroxide solution. In various aspects, the method can include storing hydrogen gas released from the cathode, such as collecting the hydrogen gas in a hydrogen storage tank.

Examples

[0054] Various aspects of the present invention can be better understood by reference to the following Examples which are offered by way of illustration. The present invention is not limited to the Examples given herein.

[0055] FIGS. 4-6 provide experimental validation that sparging an electrolyte with oxygen gas improved oxygen evolution activity and selectivity. Electrochemical measurements were performed using a three-electrode setup in 6 M KOH at 30 °C. The same electrode material was used as the working and counter electrode, with Hg/HgO as the reference electrode. Oxygen sparging was done using a PTFE bubbler. FIGS. 4A-4F illustrates polarization curves for non-platinum group metal (PGM) electrodes and PGM electrodes without any gas sparging (FIGS. 4A-4B), with oxygen sparging (FIGS. 4C-4D), and with nitrogen sparging the electrolyte (FIGS. 4E-4F). Experiments were performed in 6 M KOH at 30 °C. FIG. 4 demonstrates that the transition from oxygen evolution to hydrogen peroxide formation (ca. 1.4 - 1.6 V vs. Hg/HgO) were not electrochemically observed when the electrolyte was sparged with oxygen and nitrogen gas (an inert gas). Furthermore, sparging with oxygen and nitrogen gas improved the oxygen evolution activity as determined by lower voltages with increasing-current densities. These results demonstrated that extra convection from gas sparging suppressed side reactions and improved performance. [0056] FIG. 5 illustrates a comparison of overpotential and Tafel slope (describing the change in voltage per decade of current) for a non-platinum group metal (PGM) electrode without any gas sparging, sparging with oxygen gas, and sparging with nitrogen gas. Overpotentials associated with 100 mA cm' ² and 1 A cm' ² were extrapolated from overpotentials measured at 10 mA cm' ² using the experimental Tafel slope values. Experiments were performed in 6 M KOH at 30 °C. FIG. 6 illustrates a comparison of overpotential and Tafel slope for a platinum group metal (PGM) electrode without any gas sparging, sparging with oxygen gas, and sparging with nitrogen gas. Overpotentials associated with 100 mA cm' ² and 1 A cm' ² were extrapolated from overpotentials measured at 10 mA cm' ² using the experimental Tafel slope values. Experiments were performed in 6 M KOH at 30 °C. FIGS. 5 and 6 further demonstrate the benefits of oxygen sparging as noted by a reduced Tafel slope for non-PGM and PGM electrodes. A reduced Tafel slope indicated the oxygen evolution reaction was mechanistically eased when oxygen sparging, while no change in Tafel slope was observed during nitrogen sparging. The lower Tafel slope reduces the energy (voltage) required to drive the water electrolysis process to higher current densities. These findings demonstrated that the increased activity during nitrogen sparging vs. no sparging was solely due to increased convection, while oxygen sparging improved convection and eased the oxygen evolution reaction pathway.

[0057] The terms and expressions that have been employed are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the aspects of the present invention. Thus, it should be understood that although the present invention has been specifically disclosed by specific aspects and optional features, modification and variation of the concepts herein disclosed may be resorted to by those of ordinary skill in the art, and that such modifications and variations are considered to be within the scope of aspects of the present invention.

Exemplary Aspects. [0058] The following exemplary aspects are provided, the numbering of which is not to be construed as designating levels of importance:

[0059] Aspect 1 provides an electrochemical system comprising: an electrochemical cell comprising an anode, a cathode, and a membrane between the anode and the cathode; and an anolyte oxygen sparger than sparges a gas comprising oxygen into an anolyte that is circulated to contact the anode.

[0060] Aspect 2 provides the system of Aspect 1, wherein the membrane is an anion exchange membrane.

[0061] Aspect 3 provides the system of any one of Aspects 1-2, wherein the membrane is a cation exchange membrane.

[0062] Aspect 4 provides the system of any one of Aspects 1-3, wherein the membrane comprises a micro- or nano-porous membrane structure.

[0063] Aspect 5 provides the system of any one of Aspects 1-4, wherein the gas further comprises an inert gas.

[0064] Aspect 6 provides the system of any one of Aspects 1-5, wherein the gas further comprises nitrogen.

[0065] Aspect 7 provides the system of any one of Aspects 1-6, wherein the anode comprises a platinum group metal (PGM).

[0066] Aspect 8 provides the system of any one of Aspects 1-7, wherein the anode comprises platinum, ruthenium, iridium, or a combination thereof.

[0067] Aspect 9 provides the system of any one of Aspects 1-8, wherein the anode comprises a non-platinum group metal.

[0068] Aspect 10 provides the system of any one of Aspects 1-9, wherein the anode comprises nickel, cobalt, iron, copper, manganese, molybdenum, or a combination thereof.

[0069] Aspect 11 provides the system of any one of Aspects 1-10, wherein the anode comprises an individual element, an alloy, an oxide, or a combination thereof.

[0070] Aspect 12 provides the system of any one of Aspects 1-11, wherein the gas comprising oxygen has a concentration of oxygen of 22% to 100%. [0071] Aspect 13 provides the system of any one of Aspects 1-12, wherein the gas comprising oxygen has a concentration of oxygen of 30% to 95%.

[0072] Aspect 14 provides the system of any one of Aspects 1-13, wherein the gas comprising oxygen comprises oxygen and further comprises one or more inert gases, air, or a combination thereof.

[0073] Aspect 15 provides the system of any one of Aspects 1-14, wherein the gas comprising oxygen comprises oxygen generated by the anode.

[0074] Aspect 16 provides the system of any one of Aspects 1-15, wherein the sparger releases bubbles of the gas comprising oxygen into the anolyte from a pipe, a tube, a mesh, a sieve, a plate, a nozzle, a porous nozzle, a porous surface, or a combination thereof.

[0075] Aspect 17 provides the system of any one of Aspects 1-16, wherein the sparger releases bubbles of the gas comprising oxygen into the anolyte outside of the electrochemical cell.

[0076] Aspect 18 provides the system of any one of Aspects 1-17, wherein the oxygen sparger sparges the gas comprising oxygen into the anolyte at a rate of 0.01 mL to 100 mL per 1 mL of anolyte.

[0077] Aspect 19 provides the system of any one of Aspects 1-18, wherein the oxygen sparger sparges the gas comprising oxygen into the anolyte at a rate of 0.1 mL to 2 mL per 1 mL of anolyte.

[0078] Aspect 20 provides the system of any one of Aspects 1-19, wherein the anolyte oxygen sparger sparges the anolyte within an anolyte holding tank.

[0079] Aspect 21 provides the system of any one of Aspects 1-20, wherein the sparging of the gas comprising oxygen into the anolyte improves electrochemical performance, reduces overpotential, suppresses undesired sidereactions, or a combination thereof.

[0080] Aspect 22 provides the system of any one of Aspects 1-21, wherein the sparging of the gas comprising oxygen into the anolyte saturates the anolyte with oxygen.

[0081] Aspect 23 provides the system of any one of Aspects 1-22, wherein the anolyte having the gas comprising oxygen sparged therein has a dissolved concentration of oxygen of 10 mg/L to 200 mg/L. [0082] Aspect 24 provides the system of any one of Aspects 1-23, wherein the anolyte having the gas comprising oxygen sparged therein has a dissolved concentration of oxygen of 20 mg/L to 100 mg/L.

[0083] Aspect 25 provides the system of any one of Aspects 1-24, wherein circulating the anolyte to contact the anode further comprises circulating a gas phase to contact the anode, wherein the gas phase is circulated to contact the anode with the anolyte.

[0084] Aspect 26 provides the system of Aspect 25, wherein with respect to the anolyte the gas phase comprises headspace gas, entrained gas, or a combination thereof.

[0085] Aspect 27 provides the system of any one of Aspects 25-26, wherein the gas phase has a concentration of oxygen of 22% to 100%.

[0086] Aspect 28 provides the system of any one of Aspects 25-27, wherein the gas phase has a concentration of oxygen of 30% to 95%.

[0087] Aspect 29 provides the system of any one of Aspects 25-28, wherein the gas phase has a concentration of hydrogen in oxygen of less than 4%.

[0088] Aspect 30 provides the system of any one of Aspects 25-29, wherein the system comprises an anolyte circulation loop that circulates the anolyte and the gas phase.

[0089] Aspect 31 provides the system of Aspect 30, wherein the anolyte circulation loop has a volume ratio of anolyte to the gas phase of 0.0001 : 1 to 10000: 1.

[0090] Aspect 32 provides the system of any one of Aspects 30-31, wherein the anolyte circulation loop has a volume ratio of anolyte to the gas phase of 1 : 1 to 100: 1.

[0091] Aspect 33 provides the system of any one of Aspects 30-32, wherein the anolyte circulation loop further comprises a separator that separates at least a portion of the gas phase from the combined anolyte and gas phase.

[0092] Aspect 34 provides the system of Aspect 33, wherein a volume ratio of the portion of the gas phase separated from the gas phase to be circulated to contact the anode is 0.0001 : 1 to 10000: 1.

[0093] Aspect 35 provides the system of any one of Aspects 30-34, wherein the anolyte circulation loop further comprises an anolyte storage tank. [0094] Aspect 36 provides the system of any one of Aspects 30-35, wherein the anolyte circulation loop further comprises an oxygen storage tank.

[0095] Aspect 37 provides the system of any one of Aspects 30-36, wherein the anolyte circulation loop further comprises an electrolyte tank for supplying the anolyte.

[0096] Aspect 38 provides the system of Aspect 37, wherein the electrolyte tank further supplies catholyte that the system contacts with the catholyte.

[0097] Aspect 39 provides the system of any one of Aspects 1-38, wherein the cathode releases hydrogen gas.

[0098] Aspect 40 provides the system of any one of Aspects 1-39, wherein the system further comprises a hydrogen storage tank for collecting hydrogen gas released from the cathode.

[0099] Aspect 41 provides a method of using an electrochemical cell, the method comprising: sparging a gas comprising oxygen into an anolyte using an anolyte oxygen sparger, wherein the anolyte is circulated to contact an anode of an electrochemical cell comprising the anode, a cathode, and a membrane between the anode and the cathode.

[0100] Aspect 42 provides the method of Aspect 41, wherein the gas further comprises an inert gas.

[0101] Aspect 43 provides the method of any one of Aspects 41-42, wherein the gas further comprises nitrogen.

[0102] Aspect 44 provides the method of any one of Aspects 41-43, wherein the anode comprises a platinum group metal (PGM).

[0103] Aspect 45 provides the method of any one of Aspects 41-44, wherein the anode comprises platinum, ruthenium, iridium, or a combination thereof.

[0104] Aspect 46 provides the method of any one of Aspects 41-45, wherein the anode comprises a non-platinum group metal. [0105] Aspect 47 provides the method of any one of Aspects 41-46, wherein the anode comprises nickel, cobalt, iron, copper, manganese, molybdenum, or a combination thereof.

[0106] Aspect 48 provides the method of any one of Aspects 41-47, wherein the anode comprises an individual element, an alloy, an oxide, or a combination thereof.

[0107] Aspect 49 provides the method of any one of Aspects 41-48, wherein the anolyte oxygen sparger sparges the anolyte within a holding tank. [0108] Aspect 50 provides the method of any one of Aspects 41-49, wherein the gas comprising oxygen has a concentration of oxygen of 22% to 100%.

[0109] Aspect 51 provides the method of any one of Aspects 41-50, wherein the gas comprising oxygen has a concentration of oxygen of 30% to 95%.

[0110] Aspect 52 provides the method of any one of Aspects 41-51, wherein the gas comprising oxygen comprises oxygen and further comprises one or more inert gases, air, or a combination thereof.

[0111] Aspect 53 provides the method of any one of Aspects 41-52, wherein the gas comprising oxygen comprises oxygen generated by the anode. [0112] Aspect 54 provides the method of any one of Aspects 41-53, wherein the sparger releases bubbles of the gas comprising oxygen into the anolyte from a pipe, a tube, a mesh, a sieve, a plate, a nozzle, a porous nozzle, a porous surface, or a combination thereof.

[0113] Aspect 55 provides the method of any one of Aspects 41-54, wherein the sparger releases bubbles of the gas comprising oxygen into the anolyte outside of the electrochemical cell.

[0114] Aspect 56 provides the method of any one of Aspects 41-55, wherein the oxygen sparger sparges the gas comprising oxygen into the anolyte at a rate of 0.01 mL to 100 mL per 1 mL of anolyte.

[0115] Aspect 57 provides the method of any one of Aspects 41-56, wherein the oxygen sparger sparges the gas comprising oxygen into the anolyte at a rate of 0.1 mL to 2 mL per 1 mL of anolyte.

[0116] Aspect 58 provides the method of any one of Aspects 41-57, wherein the sparging of the gas comprising oxygen into the anolyte improves electrochemical performance, reduces overpotential, suppresses undesired sidereactions, or a combination thereof.

[0117] Aspect 59 provides the method of any one of Aspects 41-58, wherein the sparging of the gas comprising oxygen into the anolyte saturates the anolyte with oxygen.

[0118] Aspect 60 provides the method of any one of Aspects 41-59, wherein the anolyte having the gas comprising oxygen sparged therein has a dissolved concentration of oxygen of 10 mg/L to 200 mg/L.

[0119] Aspect 61 provides the method of any one of Aspects 41-60, wherein the anolyte having the gas comprising oxygen sparged therein has a dissolved concentration of oxygen of 20 mg/L to 100 mg/L.

[0120] Aspect 62 provides the method of any one of Aspects 41-61, wherein circulating the anolyte to contact the anode further comprises circulating a gas phase to contact the anode, wherein the gas phase is circulated to contact the anode with the anolyte.

[0121] Aspect 63 provides the method of Aspect 62, wherein with respect to the anolyte the gas phase comprises headspace gas, entrained gas, or a combination thereof.

[0122] Aspect 64 provides the method of any one of Aspects 62-63, wherein the gas phase has a concentration of oxygen of 22% to 100%.

[0123] Aspect 65 provides the method of any one of Aspects 62-64, wherein the gas phase has a concentration of oxygen of 30% to 95%.

[0124] Aspect 66 provides the method of any one of Aspects 62-65, wherein the gas phase has a concentration of hydrogen in oxygen of less than 4%.

[0125] Aspect 67 provides the method of any one of Aspects 62-66, wherein the method comprises circulating the anolyte and a gas phase through an anolyte circulation loop.

[0126] Aspect 68 provides the method of Aspect 67, wherein the anolyte circulation loop has a volume ratio of anolyte to the gas phase of 0.0001 : 1 to 10000: 1.

[0127] Aspect 69 provides the method of any one of Aspects 67-68, wherein the anolyte circulation loop has a volume ratio of anolyte to the gas phase of 1 : 1 to 100: 1. [0128] Aspect 70 provides the method of any one of Aspects 67-69, further comprising separating at least a portion of the gas phase from the combined anolyte and gas phase.

[0129] Aspect 71 provides the method of Aspect 70, wherein a volume ratio of the portion of the gas phase separated from the gas phase to be circulated to contact the anode is 0.0001 : 1 to 10000: 1.

[0130] Aspect 72 provides the method of any one of Aspects 67-71, wherein the anolyte circulation loop further comprises an anolyte storage tank.

[0131] Aspect 73 provides the method of any one of Aspects 67-72, wherein the anolyte circulation loop further comprises an oxygen storage tank.

[0132] Aspect 74 provides the method of any one of Aspects 41-73, further comprising supplying the anolyte from an electrolyte tank.

[0133] Aspect 75 provides the method of Aspect 74, further comprising contacting the cathode with catholyte supplied from the electrolyte tank.

[0134] Aspect 76 provides the method of any one of Aspects 41-75, wherein the cathode releases hydrogen gas.

[0135] Aspect 77 provides the method of any one of Aspects 41-76, wherein the method further comprises collecting hydrogen gas released from the cathode in a hydrogen storage tank.

[0136] Aspect 78 provides the system or method of any one or any combination of Aspects 1-77 optionally configured such that all elements or options recited are available to use or select from.