Boron phosphate matrix layer

1. A fuel cell, comprising:

a cathode electrode;

an anode electrode;

a porous matrix layer between the cathode electrode and the anode electrode, the porous matrix layer including pores and solids, the solids of the porous matrix layer comprising at least 90% boron phosphate by mass; and

a phosphoric acid electrolyte within the pores of the matrix layer.

2. The fuel cell of claim 1 , wherein

the boron phosphate has an average particle size between 0.5 μm and 4 μm.

3. The fuel cell of claim 2 , wherein the average particle size is approximately 2 μm.

4. The fuel cell of claim 1 , wherein

the matrix layer has a thickness that is between 10 μm and 100 μm.

5. The fuel cell of claim 3 , wherein the thickness is approximately 50 μm.

6. The fuel cell of claim 1 , wherein the solids comprise between 90% and 99% boron phosphate by mass.

7. The fuel cell of claim 1 , wherein the matrix layer comprises a coating on at least one of the electrodes.

8. The fuel cell of claim 1 , wherein

the cathode electrode and the anode electrode each comprises a catalyst layer;

each catalyst layer is surrounded by a porous filler band layer; and

each porous filler band layer comprises boron phosphate.

9. The fuel cell of claim 8 , wherein the filler band layers have a different composition than the matrix layer.

10. The fuel cell of claim 1 , wherein

the anode electrode and the cathode electrode are supported on respective substrate layers;

the respective substrate layers comprise an edge seal; and

the respective edge seals comprise boron phosphate.

11. A method of making a fuel cell, the method comprising:

establishing a cathode layer;

establishing an anode layer;

establishing a porous matrix layer between the cathode layer and the anode layer, the porous matrix layer including pores and solids, the solids comprising at least 90% boron phosphate by mass; and

disposing phosphoric acid electrolyte in the pores of the porous matrix layer.

12. The method of claim 11 , wherein establishing the porous matrix layer comprises

mixing a slurry comprising boron phosphate particles, a surfactant, a thickening agent, and a binder;

depositing a coating of the mixed slurry on at least one of the cathode layer or the anode layer; and

drying the deposited coating, wherein the resulting coating is at least part of the matrix layer.

13. The method of claim 12 , comprising

depositing the coating of the mixed slurry on each of the cathode layer and the anode layer; and

wherein the deposited coatings collectively establish the matrix layer.

14. The method of claim 12 , wherein

the boron phosphate particles have an average particle size between 0.5 μm and 4 μm.

15. The method of claim 14 , wherein the average particle size is approximately 2 μm.

16. The method of claim 11 , wherein

the matrix layer has a thickness that is between 10 μm and 100 μm.

17. The method of claim 16 , wherein the thickness is approximately 50 μm.

18. The method of claim 11 , wherein the solids comprise between 90% and 99% boron phosphate by mass.

19. The method of claim 11 , comprising surrounding the cathode layer and the anode layer respectively with a filler band layer that comprises boron phosphate.

20. The method of claim 11 , comprising

establishing the cathode layer on a first substrate layer;

establishing the anode layer on a second substrate layer;

providing a first edge seal on the first substrate layer; and

providing a second edge seal on the second substrate layer,

wherein the first and second edge seals comprise boron phosphate.