Patent Application
20220396888
The present disclosure is directed to electrolyzers in general and to a coating for bipolar plates and anode gas diffusion layer/porous transport layer for an electrolyzer and method of making thereof in particular.
Proton exchange membrane (PEM) electrolyzers may be used to convert water into separate hydrogen and oxygen streams. Such PEM electrolyzers include a polymer electrolyte located between an anode electrode and a cathode electrode. Anode side and cathode side porous gas diffusion layers are located adjacent to the respective anode and cathode electrodes.
Currently, PEM electrolyzers operate in oxidizing environments that cause corrosion of various electrolyzer components. The oxidation increases electrical resistance of the electrolyzer components and thus reduces efficiency. What is needed are PEM electrolyzer components that are resistant to corrosion.
Provided herein is a proton exchange membrane (PEM) electrolyzer component comprising at least one of a bipolar plate or porous transport layer, the electrolyzer component comprising an electrically conductive and oxidatively stable coating comprising an electrically conductive metal nitride or an electrically conductive metal oxide on at least one surface thereof. In some embodiments, the electrolyzer component comprises the bipolar plate. In some other embodiments, the electrolyzer component comprises the porous transport layer. In some particular embodiments, the porous transport layer comprises a porous titanium sheet.
In some embodiments, the electrically conductive and oxidatively stable coating comprises the electrically conductive metal nitride. In some aspects, the electrically conductive metal nitride comprises at least one of titanium nitride (TiN), tungsten nitride (WN), or tantalum nitride (TaN).
In some embodiments, the electrically conductive and oxidatively stable coating comprises the electrically conductive metal oxide. In some aspects, the electrically conductive metal oxide is selected from the group consisting of a metal rich titanium oxide having a formula TiO2-x, where 0.1≤x≤0.9; dioxides of tin (Sn) or lead (Pb); manganese oxide; metal rich zirconium oxide having a formula ZrO2-x where 0.1≤x≤0.9; rhenium oxide; iridium oxide; cobalt oxide; tungsten oxide; a mixed metal oxide; and combinations thereof.
In some embodiments, the electrically conductive and oxidatively stable coating comprises the electrically conductive metal nitride and the electrically conductive metal oxide.
In some embodiments, the electrically conductive and oxidatively stable coating has a thickness of about 0.2 microns to about 2 microns.
Further provided herein is a PEM electrolyzer comprising an anode side flow plate, the anode side flow plate and the porous transport layer of the present disclosure located on an anode side of the electrolyzer; a cathode side flow plate; a PEM polymer electrolyte located between the anode side flow plate and the cathode side flow plate; an anode electrode located between the porous transport layer and the PEM polymer electrolyte; a cathode side gas diffusion layer located between the PEM polymer electrolyte and the cathode side flow plate; and a cathode electrode located between the cathode side gas diffusion layer and the PEM polymer electrolyte.
Further provided herein is a method comprising coating a proton exchange membrane (PEM) electrolyzer component comprising at least one of a bipolar plate or porous transport layer with an electrically conductive and oxidatively stable coating comprising an electrically conductive metal nitride or an electrically conductive metal oxide on at least one surface thereof. In some embodiments, the electrolyzer component comprises the bipolar plate. In some other embodiments, the electrolyzer component comprises the porous transport layer. In some particular embodiments, the porous transport layer comprises a porous titanium sheet.
In some embodiments, the electrically conductive and oxidatively stable coating comprises the electrically conductive metal nitride. In some aspects, the electrically conductive metal nitride comprises at least one of titanium nitride (TiN), tungsten nitride (WN), or tantalum nitride (TaN).
In some embodiments, the electrically conductive and oxidatively stable coating comprises the electrically conductive metal oxide. In some aspects, the electrically conductive metal oxide is selected from the group consisting of a metal rich titanium oxide having a formula TiO2-x, where 0.1≤x≤0.9; dioxides of tin (Sn) or lead (Pb); manganese oxide; metal rich zirconium oxide having a formula ZrO2-x, where 0.1≤x≤0.9; rhenium oxide; iridium oxide; cobalt oxide; tungsten oxide; a mixed metal oxide; and combinations thereof.
In some embodiments, the electrically conductive and oxidatively stable coating comprises the electrically conductive metal nitride and the electrically conductive metal oxide.
In some embodiments, the electrically conductive and oxidatively stable coating has a thickness of about 0.2 microns to about 2 microns.
In some embodiments, the coating step is accomplished by sputtering. In some other embodiments, the coating step is accomplished by stamping, a powder metallurgy process, or a tape casting method.
In some embodiments, the electrically conductive and oxidatively stable coating is formed in situ. In an example, the component comprises the porous transport layer and the porous transport layer comprises a porous titanium sheet formed by powder metallurgy.
Provided herein are electrolyzer components coated with an electrically conductive and oxidatively stable coating. The coating comprises at least one of an electrically conductive metal nitride or an electrically conductive metal oxide. The coating protects the electrolyzer component from oxidation while providing little electrical resistance and therefore exhibit higher electrochemical stability and electrical conductivity as compared to electrolyzer components that lack the coating of the present disclosure. As used herein, “electrochemical stability” refers to an electrolyzer component's resistance to corrosion when exposed to high voltage (e.g., about 2.5 V). Thus, an electrolyzer component with high electrochemical stability is highly resistant to corrosion when exposed to high voltage.
The electrolyzer component may comprise a bipolar plate or a porous transport layer of an electrolyzer. In one embodiment, the electrically conductive and oxidatively stable coating (also referred to as a protection layer) is provided on one or both bipolar plates (i.e., flow plates) and/or on a porous transport layer of a proton exchange membrane (PEM) electrolyzer. The porous transport layer may be a porous titanium sheet configured to function as an anode side gas diffusion layer as described further herein. Examples of bipolar plates suitable for this purpose are described in more detail in U.S. application Ser. No. 17/402,821, the entire contents of which are incorporated by reference herein. Examples of porous transport layers are described in more detail in U.S. application Ser. No. 17/384,033, the entire contents of which are incorporated by reference herein.
The electrically conductive and oxidatively stable coating comprises at least one electrically conductive metal oxide or at least one electrically conductive metal nitride coating. The coating may contain an oxide or nitride of a single metal or of two or more metals. The coating may be applied to at least one surface of the electrolyzer component, a portion of at least one surface of the electrolyzer component, or the coating may be applied to the entire surface of the electrolyzer component.
Examples of the electrically conductive metal oxide or electrically conductive metal nitride include one or more electrically conductive metal nitrides, such as TiN, WN, or TaN; and/or one or more electrically conductive metal oxides, such as metal rich titanium oxides (TiO2-x, where 0.1≤x≤0.9; also referred to herein as “titanium suboxides”), dioxides of Sn or Pb (including fluorine-doped tin oxide), manganese oxides (e.g., manganese dioxide, MnO2), metal rich zirconium oxides (ZrO2-x, where 0.1≤x≤0.9), rhenium, cobalt, iridium or tungsten oxides, or mixed metal oxides, such as indium tin oxide, aluminum zinc oxide, lanthanum strontium manganate, etc.
In some aspects when the coating comprises a metal rich zirconium oxide ZrO2-x, x may be greater than or equal to about 0.1, about 0.2, about 0.3, about 0.4, about 0.5, about 0.6, about 0.7, about 0.8, or less than or equal to 0.9. In some additional aspects, x may be from about 0.1 to about 0.2, about 0.1 to about 0.3, about 0.1 to about 0.4, about 0.1 to about 0.5, about 0.1 to about 0.6, about 0.1 to about 0.7, about 0.1 to about 0.8, from about 0.2 to about 0.9, from about 0.3 to about 0.9, from about 0.4 to about 0.9, from about 0.5 to about 0.9, from about 0.6 to about 0.9, from about 0.7 to about 0.9, or from about 0.8 to about 0.9.
In some aspects when the coating comprises a metal rich titanium oxide TiO2-x, x may be greater than or equal to about 0.1, about 0.2, about 0.3, about 0.4, about 0.5, about 0.6, about 0.7, about 0.8, or less than or equal to 0.9. In some additional aspects, x may be from about 0.1 to about 0.2, about 0.1 to about 0.3, about 0.1 to about 0.4, about 0.1 to about 0.5, about 0.1 to about 0.6, about 0.1 to about 0.7, about 0.1 to about 0.8, from about 0.2 to about 0.9, from about 0.3 to about 0.9, from about 0.4 to about 0.9, from about 0.5 to about 0.9, from about 0.6 to about 0.9, from about 0.7 to about 0.9, or from about 0.8 to about 0.9.
The electrically conductive metal oxide or electrically conductive metal nitride coating may further include a dopant. Dopants may enhance the electrical conductivity of the coating. The dopant may include dopants known in the art to increase electrical conductivity, such as niobium. The dopant may be present in an amount of about 1% to about 2% by weight of the coating; for example, the dopant may be present in an amount of about 1.0%, about 1.1%, about 1.2%, about 1.3%, about 1.4%, about 1.5%, about 1.6%, about 1.7%, about 1.8%, about 1.9%, or about 2.0% by weight of the coating.
The coating may contain at least one of the above electrically conductive metal nitrides, at least one of the above electrically conductive metal oxides, or may contain a mixture of two or more electrically conductive metal nitrides, a mixture of two or more electrically conductive metal oxides, or a mixture of at least one electrically conductive metal nitride and at least one electrically conductive metal oxide. When the coating comprises an electrically conductive metal nitride and an electrically conductive metal oxide, the coating may be a mixture or a combination of the electrically conductive metal nitride and the electrically conductive metal oxide, or the coating may comprise at least two coating layers, each coating layer comprising one of the electrically conductive metal nitride and the electrically conductive metal oxide.
When the coating contains at least one metal nitride and at least one metal oxide, the at least one metal nitride may be present in an amount of from about 10% to about 90% by weight of the coating. For example, the at least one metal nitride may be present in an amount of from about 10% to about 20%, about 10% to about 30%, about 10% to about 40%, about 10% to about 50%, about 10% to about 60%, about 10% to about 70%, about 10% to about 80%, about 20% to about 90%, about 30% to about 90%, about 40% to about 90%, about 50% to about 90%, about 60% to about 90%, about 70% to about 90%, or about 80% to about 90% by weight of the coating.
When the coating contains at least one metal nitride and at least one metal oxide, the at least one metal oxide may be present in an amount of from about 10% to about 90% by weight of the coating. For example, the at least one metal oxide may be present in an amount of from about 10% to about 20%, about 10% to about 30%, about 10% to about 40%, about 10% to about 50%, about 10% to about 60%, about 10% to about 70%, about 10% to about 80%, about 20% to about 90%, about 30% to about 90%, about 40% to about 90%, about 50% to about 90%, about 60% to about 90%, about 70% to about 90%, or about 80% to about 90% by weight of the coating.
The coating may have a thickness from about 0.2 to about 2 microns, such as from about 0.2 microns to about 0.4 microns, about 0.2 microns to about 0.6 microns, about 0.2 microns to about 0.8 microns, about 0.2 microns to about 1 micron, about 0.2 microns to about 1.2 microns, about 0.2 microns to about 1.4 microns, about 0.2 microns to about 1.6 microns, about 0.2 microns to about 1.8 microns, about 0.4 microns to about 2 microns, about 0.6 microns to about 2 microns, about 0.8 microns to about 2 microns, about 1 micron to about 2 microns, about 1.2 microns to about 2 microns, about 1.4 microns to about 2 microns, about 1.6 microns to about 2 microns, or about 1.8 microns to about 2 microns. In some particular embodiments, the coating may have a thickness of less than about 0.2 microns. Thicker coatings tend to have higher electrical resistance; therefore, smaller coating thicknesses are preferred.
The coated electrolyzer component may have a lower interfacial resistance as compared to an electrolyzer lacking a coating of the present disclosure. The interfacial resistance as used herein refers to the electrical resistance between the coating and the electrolyzer component, and the coated electrolyzer component and a membrane (e.g., a polymer exchange membrane). Stated another way, the interfacial resistance refers to the electrical resistance across the coating, including any voltage losses from electricity transferring to or from the coating.
The interfacial resistance of the coated electrolyzer component may be from about 0.1 to about 5 milliohm·cm2; for example, the interfacial resistance of the coated electrolyzer component may be from about 0.1 to about 0.5 milliohm·cm2, about 0.1 to about 1 milliohm·cm2, about 0.1 to about 1.5 milliohm·cm2, about 0.1 to about 2 milliohm·cm2, about 0.1 to about 2.5 milliohm·cm2, about 0.1 to about 3 milliohm·cm2, about 0.1 to about 3.5 milliohm·cm2, about 0.1 to about 4 milliohm·cm2, about 0.1 to about 4.5 milliohm·cm2, 0.5 to about 5 milliohm·cm2, about 1 to about 5 milliohm·cm2, about 1.5 to about 5 milliohm·cm2, about 2 to about 5 milliohm·cm2, about 2.5 to about 5 milliohm·cm2, about 3 to about 5 milliohm·cm2, about 3.5 to about 5 milliohm·cm2, about 4 to about 5 milliohm·cm2, or about 4.5 to about 5 milliohm·cm2. The interfacial resistance is preferably about 2 milliohm·cm2.
The electrolyzer component may also include a transport layer. A porous titanium layer (e.g., sheet) may be used as the anode side gas diffusion layer (i.e., transport layer) 114. In one embodiment, the porous titanium layer (e.g., sheet) that is used as an anode side gas diffusion layer 114 is formed by a powder process. In some embodiments, the powder process may include tape casting, physical vapor deposition, or powder pressing. After sintering the titanium sheet, it is coated on both sides (e.g., on the anode electrode side and the flow plate side) with the electrically conductive metal nitride or electrically conductive metal oxide coating to provide good conductivity and corrosion resistance.
The porous titanium layer may have a porosity of about 30% to about 50%. Methods for determining the porosity of a material are generally well known in the art. In some examples, the titanium layer may have a porosity of about 30% to about 35%, about 30% to about 40%, about 30% to about 45%, about 35% to about 40%, about 35% to about 45%, about 35% to about 50%, about 40% to about 45%, about 40% to about 50%, or about 45% to about 50%.
The anode side flow plate 102 may include a water inlet opening 108, an oxygen outlet opening 109 and a water flow channel (e.g. tortuous path groove) 106 connecting the water inlet opening 108 and the oxygen outlet opening 109 in the side of the flow plate 102 facing the anode side gas diffusion layer 114. The anode side gas diffusion layer 114 may include a porous titanium layer. The cathode side gas diffusion layer 118 may include a porous carbon layer. The anode electrode 116 may include any suitable anode catalyst, such as an iridium layer. The cathode electrode 120 may include any suitable cathode catalyst, such as a platinum layer or a platinum on carbon layer. Other noble metal catalyst layers may also be used for the anode and/or cathode electrodes. The electrolyte 112 may include any suitable proton exchange (e.g., hydrogen ion transport) polymer membrane, such as a Nafion® membrane composed of sulfonated tetrafluoroethylene based fluoropolymer-copolymer having a formula C7HF13O5S.C2F4.
In operation, water is provided into the water flow channel 106 through the water inlet opening 108. The water flows through the water flow channel 106 and through the anode side gas diffusion layer 114 to the anode electrode 116. The water is electrochemically separated into oxygen and hydrogen at the anode electrode 116 upon an application of an external current or voltage between the anode electrode 116 and the cathode electrode 120. The oxygen diffuses back through the anode side gas diffusion layer 114 to the anode side flow plate 102 and exits the electrolyzer 100 through the oxygen outlet opening 109. The hydrogen ions diffuse through the electrolyte 112 to the cathode electrode 120 and then exit the electrolyzer 100 through the cathode side gas diffusion layer 118 and the hydrogen outlet opening 110 in the cathode side flow plate 104.
Further provided herein is a method comprising coating a proton exchange membrane electrolyzer component. The electrolyzer component may be any electrolyzer component described herein, and preferably comprises at least one of a bipolar plate or a porous transport layer with an electrically conductive and oxidatively stable coating. The electrically conductive and oxidatively stable coating may be any coating of the present disclosure, and preferably comprises an electrically conductive metal nitride or an electrically conductive metal oxide on at least one surface of the electrolyzer component. The method may further comprise incorporating the coated electrolyzer component into a PEM electrolyzer.
The coating step may be accomplished by any suitable method known in the art, such as physical vapor deposition (e.g., sputtering), powder metallurgy, stamping, screen printing, or tape casting. In preferred embodiments, the coating is formed via screen printing or tape casting.
In preferred embodiments, the coating may be formed prior to sintering the electrolyzer component; i.e., in situ. By forming the coating in situ, the interfacial resistance of the electrolyzer component is greatly reduced as compared to a coating formed after sintering. In situ coatings may be formed by powder metallurgy, stamping, screen printing, or tape casting.
The coating may be accomplished via tape casting.
The slip material 502 is dispensed from the dispensing chamber 504 onto a moving tape carrier web 506. The tape carrier web 506 may comprise a metal (e.g., steel), glass, polymer, etc., belt that moves past a doctor blade 508. The slip material 502 moving on the tape carrier web 506 under the doctor blade 508 is flattened into a green titanium containing tape 510 by the doctor blade 508. Green titanium containing tapes 510 of various blends of powder sizes, specific content and solid ratios can be produced with slight variations of the slip material (i.e., slurry) 502 formulations.
The tape carrier web 506 may then move the green titanium containing tape 510 through a drying chamber 512. The drying chamber 512 may include a heated air inlet 514 and a saturated air outlet 516. The heated air (or another source of heat) dries the green titanium containing tape 510, and the solvent which is evaporated from the tape 510 is removed with the air through the saturated air outlet 516. The dried green titanium containing tape 510 may then by cut into titanium green sheets 510S having the shape of the anode side gas diffusion layer in a cutting station 518.
The dried green titanium containing tape 510 that has been cut into the titanium green sheets 510S is subsequently sintered in the sintering chamber 520 at a desired temperature to form the anode side gas diffusion layers 114. Preferably, the titanium green sheets 510S are sintered in an oxygen-free or a low oxygen atmosphere at 1000 to 1100 degrees C. The atmosphere may comprise an inert atmosphere of any suitable inert gas, such as a noble gas, such as argon. The atmosphere may comprise an oxygen partial pressure of less than 0.1 atm, such as 0.0001 to 0.01 atm.
In one embodiment, the dried green titanium containing tape 510 may be provided from the drying chamber 512 into the cutting station 518 and the cut tape (i.e., titanium green sheets 510S) is then provided from the cutting station 518 into a sintering chamber 520 for sintering using the same tape carrier web 506. Optionally, additional chambers, such as a de-bindering chamber, may be located between the drying chamber 512 and the sintering chamber 520 if a de-bindering step which is carried out at a temperature between the drying and sintering temperatures is desired.
The sintering chamber 520 may comprise a resistively or gas heated continuous furnace (e.g., belt furnace). In such embodiments, the dried green titanium containing tape 510 (i.e., the titanium green sheet 510S) moves through the drying chamber 512, the cutting station 518 and the continuous furnace on the same tape carrier web 506. In another embodiment, the sintering chamber 520 may comprise a rapid thermal annealing (“RTA”) apparatus (also referred to as a rapid thermal processing (“RTP”) apparatus) in which the cut dried green titanium containing tape 510 (i.e., the titanium green sheet 510S) is heated by a flash lamp or a laser beam. In this embodiment, the green titanium containing tape 510 moves through the drying chamber 512, the cutting station 518 and the RTA apparatus on the same tape carrier web 506. Thus, the steps of flattening the slip material 502, drying the tape, cutting the tape and sintering the cut tape may occur continuously on the same moving tape carrier web 506.
The sintering chamber 520 may comprise an upstream portion 520A and a downstream portion 520B which is located downstream of the upstream portion 520A with respect to the moving direction of the tape carrier web 506. An optional partition 520P may be provided between the upstream and the downstream portions of the sintering chamber 520. The upstream portion 520A may be maintained in an oxygen free or low oxygen atmosphere, such as a noble gas (e.g., argon) atmosphere. The downstream portion 520B may be maintained in a nitrogen containing atmosphere, such as a nitrogen gas or ammonia containing atmosphere (e.g., a low pressure or vacuum atmosphere with a nitrogen containing gas partial pressure). The titanium green sheet 510S may be reactively sintered in the downstream portion 520B to form a titanium nitride or a titanium oxide layer on its surface. This coating improves the performance of the titanium gas diffusion layer 114.
In alternative embodiments, the slip material 502 may be provided onto the tape carrier web 506 from the side and/or from the bottom instead of from the top as shown in
Plates as described in the present disclosure were provided and coated with either a gold (Au) coating or a titanium suboxide coating. The plates were incorporated into an electrochemical cell, wherein the coated plates acted as electrodes. The electrodes were subjected to a highly oxidative positive potential against a platinum counter electrode. The gold-coated plate was exposed to a potential of 2 V, and the titanium coated plate was exposed to potentials of 2 V and 2.4 V. The electrochemical activity was determined by measuring the current flow, which is shown in
As can be seen in
Concentrations, amounts, and other numerical data may be expressed or presented herein in a range format. It is to be understood that such a range format is used merely for convenience and brevity and should be interpreted flexibly 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. As an illustration, a numerical range of “about 2 to about 50” should be interpreted to include not only the explicitly recited values of 2 to 50, but also include all individual values and sub-ranges within the indicated range. Thus, included in this numerical range are individual values such as 2, 2.4, 3, 3.7, 4, 5.5, 10, 10.1, 14, 15, 15.98, 20, 20.13, 23, 25.06, 30, 35.1, 38.0, 40, 44, 44.6, 45, 48, and sub-ranges such as from 1-3, from 2-4, from 5-10, from 5-20, from 5-25, from 5-30, from 5-35, from 5-40, from 5-50, from 2-10, from 2-20, from 2-30, from 2-40, from 2-50, etc. This same principle applies to ranges reciting only one numerical value as a minimum or a maximum. Furthermore, such an interpretation should apply regardless of the breadth of the range or the characteristics being described.
As used herein, the term “about” is used to provide flexibility to a numerical range endpoint by providing that a given value may be “a little above” or “a little below” the endpoint. For example, the endpoint may be within 10%, 8%, 5%, 3%, 2% or 1% of the listed value. Further, for the sake of convenience and brevity, a numerical range of “about 50 mg/mL to about 80 mg/mL” should also be understood to provide support for the range of “50 mg/mL to 80 mg/mL.”
Although the foregoing refers to particular preferred embodiments, it will be understood that the invention is not so limited. It will occur to those of ordinary skill in the art that various modifications may be made to the disclosed embodiments and that such modifications are intended to be within the scope of the invention. All of the publications, patent applications and patents cited herein are incorporated herein by reference in their entirety.
This application claims priority to U.S. Provisional Application No. 63/208,589 entitled “ELECTROLYZER BIPOLAR PLATES AND POROUS GAS DIFFUSION LAYER HAVING AN OXIDATIVELY STABLE AND ELECTRICALLY CONDUCTIVE COATING AND METHOD OF MAKING THEREOF”, filed Jun. 9, 2021, the entire contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63208589 | Jun 2021 | US |
