Water electrolyzers employing anion exchange membranes
A water electrolyzer comprises an electrolyzer stack comprising at least two electrochemical cells. Each cell comprises an anion exchange membrane, a base metal anode electrocatalyst, a base metal cathode electrocatalyst, and a sufficiently long ion conduction path between adjacent cells such that shunt currents are less than 1% of the total current supplied to the stack.
1. A water electrolyzer for producing hydrogen gas comprising an electrolyzer stack, the stack comprising at least two electrochemical cells, each of said cells comprising:
(a) an anode comprising an anode gas diffusion layer (GDL) and a quantity of anode electrocatalyst;
(b) a cathode comprising a cathode GDL and a quantity of cathode electrocatalyst;
(c) a source of a solution comprising water directed to at least one of said anode and said cathode;
(d) an anion exchange membrane interposed between said anode and said cathode,
wherein each of said anion exchange membranes has an average thickness (t) and,
wherein a shortest ion conduction path (L GDLA ) between the anode GDL of any two of the cells in the stack is: L GDLA >10*t*σ sol /σ mem
where σ sol is the conductivity (S/cm) of the solution at 60° C. and σ mem is the conductivity of each of said membranes measured in 1 M KOH at 60° C.,
wherein L GDLA >3 cm.
2. The water electrolyzer of claim 1 , wherein:
L GDLA >50* t*σ sol /σ mem .
3. The water electrolyzer of claim 1 , wherein the shortest ion conduction path (L GDLC ) between the cathode GDL of any two of the cells in the stack is:
L GDLC >10* t*σ sol /σ mem .
4. The water electrolyzer of claim 1 , wherein said solution has a pH greater than 8 at 25° C.
5. The water electrolyzer of claim 4 , wherein said solution has a pH greater than 12 at 25° C.
6. The water electrolyzer of claim 1 , wherein said solution has a conductivity greater than 0.05 S/cm at 25° C.
7. The water electrolyzer of claim 1 , wherein said cathode electrocatalyst in each of said cells is in the form of unsupported particles or particles supported on an electrically conductive support, said particles having an average size between 0.6 nm and 100 nm.
8. The water electrolyzer of claim 1 , wherein said anode electrocatalyst in each of said cells comprises a base metal catalyst.
9. The water electrolyzer of claim 8 , wherein said anode electrocatalyst in each of said cells consists essentially of one or more base metal catalysts.
10. The water electrolyzer of claim 1 , wherein said cathode electrocatalyst in each of said cells comprises a base metal catalyst.
11. The water electrolyzer of claim 10 , wherein said cathode electrocatalyst in each of said cells consists essentially of one or more base metal catalysts.
12. The water electrolyzer of claim 1 , wherein said membrane in each of said cells comprises positively charged cyclic amines.
13. The water electrolyzer of claim 12 , wherein said positively charged amines are imidazoliums, piperidiniums or pyridiniums.
14. The water electrolyzer of claim 1 , wherein said cathode in each of said cells comprises an ionomer.
15. An AEM water electrolyzer for converting water into substantially O 2 and H 2 comprising:
an electrolyzer stack, said electrolyzer stack comprising at least two electrochemical cells, each of said cells comprising:
(a) an anode comprising an anode gas diffusion layer (GDL) and a quantity of anode electrocatalyst;
(b) a cathode comprising a cathode GDL and a quantity of cathode electrocatalyst;
(c) a source of a solution comprising water directed to at least one of said anode and said cathode;
(d) an anion exchange membrane interposed between said anode and said cathode,
wherein a shortest ion conduction path (L GDLA ) between the anode GDL of any of the two cells of said at least two electrochemical cells in the stack is greater than 3 cm.