Porous electrolyzer gas diffusion layer and method of making thereof
A porous titanium sheet configured to function as an anode side gas diffusion layer of a proton exchange membrane (PEM) electrolyzer is formed by a powder technique, such as tape casting or powder metallurgy.
1. A porous titanium sheet configured to function as an anode side gas diffusion layer of a proton exchange membrane (PEM) electrolyzer, wherein the porous titanium sheet is formed by a powder technique,
wherein a first major side of the porous titanium sheet includes a groove and an opposite second major side of the porous titanium sheet has a substantially planar surface which lacks a groove,
wherein the first major side of the porous titanium sheet has a higher porosity than the opposite second major side of the porous titanium sheet,
wherein a continuous porosity gradient is formed between the first major side of the porous titanium sheet and the opposite second major side of the porous titanium sheet,
wherein the porous titanium sheet comprises conductive vias extending through the porous titanium sheet in a thickness direction of the porous titanium sheet, the conductive vias comprising particles of titanium hydride, and
wherein the porous titanium sheet includes a bimodal pore size distribution.
2. The porous titanium sheet of claim 1 , wherein the first major side of the porous titanium sheet is configured to face an anode side flow plate, and the second major side of the porous titanium sheet is configured to face an anode electrode.
3. The porous titanium sheet of claim 1 , wherein the first major side of the porous titanium sheet has a porosity which is at least 10 percent higher than a porosity of the opposite second major side of the porous titanium sheet.
4. The porous titanium sheet of claim 1 , wherein:
the porous titanium sheet contains a titanium nitride coating on at least one surface thereof; and
the porous titanium sheet comprises pure titanium or an alloy of titanium containing more than 50 atomic percent titanium and less than 50 atomic percent of at least one of molybdenum, vanadium, niobium, tantalum, or zirconium.
5. The porous titanium sheet of claim 1 , wherein the bimodal pore size distribution comprises micropores having an average pore size in a range of 1 to 5 microns and macropores having an average pore size in a range of 30 to 40 microns.
6. The porous titanium sheet of claim 1 , wherein the conductive vias further comprise a noble metal, wherein the noble metal comprises ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, or gold.
7. The porous titanium sheet of claim 1 , wherein the particles of titanium hydride have an average diameter within 20% of the thickness of the porous titanium sheet.
8. The porous titanium sheet of claim 1 , wherein the conductive vias include wires.
9. The porous titanium sheet of claim 8 , wherein the wires have an average length within 20% of the thickness of the porous titanium sheet.
10. A PEM electrolyzer, comprising:
an anode side flow plate;
a cathode side flow plate;
a PEM polymer electrolyte located between the anode side flow plate and the cathode side flow plate;
an anode side gas diffusion layer comprising the porous titanium sheet of claim 1 located between the electrolyte and the anode side flow plate;
an anode electrode located between the anode side gas diffusion layer and the electrolyte;
a cathode side gas diffusion layer located between the electrolyte and the cathode side flow plate; and
a cathode electrode located between the cathode side gas diffusion layer and the electrolyte, wherein:
the first major side of the porous titanium sheet has a higher porosity than an opposite second major side of the porous titanium sheet, and
a continuous porosity gradient is formed between the first major side of the porous titanium sheet and the opposite second major side of the porous titanium sheet.
11. The PEM electrolyzer of claim 10 , wherein:
the first major side of the porous titanium sheet faces the anode side flow plate, and the second major side of the porous titanium sheet faces the anode electrode; or
the first major side of the porous titanium sheet has the porosity which is at least 10 percent higher than the opposite second major side of the porous titanium sheet; or
a first major surface of the anode side flow plate which faces the anode side gas diffusion layer contains a water flow channel groove, the first major side of the porous titanium sheet which faces the first major surface of the anode side flow plate includes a groove which is a substantial mirror image of the water flow channel groove, and the opposite second major side of the porous titanium sheet has a substantially planar surface which lacks a groove.
12. A method, comprising making the porous titanium sheet of claim 1 configured to function as an anode side gas diffusion layer of a proton exchange membrane (PEM) electrolyzer by a powder technique.
13. The method of claim 12 , wherein the powder technique comprises tape casting.
14. The method of claim 13 , wherein the tape casting comprises:
mixing a titanium containing powder with a binder, solvent and plasticizer to form a slip material;
dispensing the slip material onto tape carrier web;
flattening the slip material moving on the tape carrier web into a green titanium containing tape using a doctor blade;
drying the green titanium containing tape;
cutting the green titanium containing tape into a first titanium green sheet having a first porosity; and
sintering the first titanium green sheet to form the porous titanium sheet.
15. The method of claim 14 , wherein:
the titanium containing powder comprises a mixture of elemental titanium and titanium hydride powders; and
the titanium hydride powder is thermally converted to elemental titanium in an exothermic reaction.
16. The method of claim 14 , further comprising adding a pore former material to the slip material and removing the pore former material during the sintering to form pores in the porous titanium sheet.
17. The method of claim 14 , wherein the steps of flattening, drying, cutting and sintering occur continuously on a same moving tape carrier web.
18. The method of claim 14 , further comprising placing a second titanium green sheet having a second porosity different from the first porosity of the first titanium green sheet prior to the sintering.
19. The method of claim 18 , wherein:
the first and the second titanium green sheets are sintered in contact with each other such that a first major side of the porous titanium sheet has a higher porosity than an opposite second major side of the porous titanium sheet; and
the first major side of the porous titanium sheet is configured to face an anode side flow plate, and the second major side of the porous titanium sheet is configured to face an anode electrode.
20. The method of claim 14 , wherein:
the titanium containing powder comprises particles having an average diameter less than 50% of a thickness of the porous titanium sheet;
the titanium containing powder is further mixed with at least one of additional titanium containing particles having an average diameter that is within 20% of the thickness of the porous titanium sheet or titanium containing wires having an average length that is within 20% of the thickness of the porous titanium sheet;
and the at least one of the additional titanium containing particles or the titanium containing wires extend through an entire thickness of the porous titanium sheet and function as the conductive vias.
21. The method of claim 12 , further comprising reactively sintering the porous titanium sheet in a nitrogen containing atmosphere to form a titanium nitride coating on at least one surface of the porous titanium sheet.
22. The method of claim 12 , further comprising placing the porous titanium sheet into the PEM electrolyzer.