Eulytite solid acid electrolytes for electrochemical devices
Improved solid acid electrolyte materials, methods of synthesizing such materials, and electrochemical devices incorporating such materials are provided. The stable electrolyte material comprises a solid acid in a eulytine structure capable of undergoing rotational disorder of oxyanion groups and capable of extended operation at elevated temperatures, that is, solid acids having hydrogen bonded anion groups; a superprotonic disordered phase; and capable of operating at temperatures of ˜100° C. and higher.
1. A compound of Formula I:
M 4a H b (XO c ) 3a ,
wherein
M is at least one metal each independently a metal cation;
X is at least one member each independently selected from the group consisting of P, Si, As, Ge, S, Se, W, Cr and V; and
each of subscript a, b and c are independently a positive real number.
2. The compound of claim 1 , having Formula II:
M 2+ 4 H(XO 4 ) 3
wherein M 2+ is a metal cation having a +2 charge.
3. The compound of claim 1 , having Formula III:
M 2+ 3 M 3+ H b (XO 4 ) 3−b (X′O 4 ) b
wherein M 2+ is a metal cation having a +2 charge;
M 3+ is a metal cation having a +3 charge;
X is a member selected from the group consisting of P, V and As; and
X′ is a member selected from the group consisting of Si and Ge.
4. The compound of claim 1 , having Formula IV:
M 1+ b M 2+ 3−b M 3+ H b (XO 4 ) 3
wherein M 1+ is a metal cation having a +1 charge;
M 2+ is a metal cation having a +2 charge; and
M 3+ is a metal cation having a +3 charge.
5. The compound of claim 1 , having Formula V:
M 1+ b M 2+ (4n−1−b) M (2+n) H b (XO 4 ) 3n
wherein M 1+ is a metal cation having a +1 charge;
M 2+ is a metal cation having a +2 charge;
M (2+n) is a metal cation having a +3, +4 or +5 charge; and
subscript n is a positive real number.
6. The compound of claim 1 , having formula VI:
M 2+ (4n−1) M (2+n−b) H b (XO 4 ) 3n
wherein M 2+ is a metal cation having a +2 charge;
M (2+n−b) is a metal cation having a +3, +4 or +5 charge; and
subscript n is a positive real number.
7. A proton conducting membrane comprising a solid acid of Formula I:
M 4a H b (XO c ) 3a ,
wherein M is at least one metal each independently a metal cation;
X is at least one member each independently selected from the group consisting of P, Si, As, Ge, S, Se, W, Cr and V; and
each of subscript a, b and c are independently a positive real number.
8. The proton conducting membrane of claim 7 , further comprising a structural binder.
9. The proton conducting membrane of claim 8 , wherein said structural binder is a member selected from the group consisting of carbon, polymer, ceramic, glass, semiconductor and metal.
10. The proton conducting membrane of claim 9 , wherein said structural binder is electrically conducting.
11. The proton conducting membrane of claim 10 , wherein said structural binder is a conducting polymer.
12. The proton conducting membrane of claim 10 , wherein said structural binder is a metal.
13. The proton conducting membrane of claim 12 , wherein said metal structural binder is mixed with a polymer.
14. The proton conducting membrane of claim 9 , wherein said structural binder is silicon dioxide.
15. The proton conducting membrane of claim 14 , wherein said structural binder is quartz.
16. The proton conducting membrane of claim 14 , wherein said structural binder is fumed silica or colloidal silica.
17. The proton conducting membrane of claim 7 , further comprising a separate conducting material.
18. The proton conducting membrane of claim 17 , wherein said separate conducting material is ionically conductive.
19. The proton conducting membrane of claim 7 , wherein said solid acid includes at least one variable valence element.
20. The proton conducting membrane of claim 7 , being thermally stable at temperatures above about 100° C.
21. The proton conducting membrane of claim 7 , having a proton conductivity of about 10 −5 Ω −1 cm −1 or higher at the temperature of use.
22. The proton conducting membrane of claim 7 , conducting both protons and electrons.
23. A method of making a compound of Formula I:
M 4a H b (XO c ) 3a ,
wherein M is at least one metal each independently a metal cation; X is at least one member each independently selected from the group consisting of P, Si, As, Ge, S, Se, W, Cr and V; each of subscript a, b and c are independently a positive real number;
comprising the steps of:
a) contacting said metal with a suitable oxyanion and a suitable hydrogen source;
b) conducting said method of making under appropriate reaction conditions so as to make a compound of Formula I.
24. The method of claim 23 , further comprising the following step:
c) dissolving said metal in a suitable solvent in the presence of a chelating agent.
25. The method of claim 23 , wherein the appropriate reaction conditions are above 500° C.
26. The method of claim 25 , further comprising the steps of cooling and rehydrating.
27. The method of claim 23 , wherein the appropriate reaction conditions involve a temperature greater than about 100° C. and a pressure greater than about 1 atm.
28. The method of claim 23 , wherein the appropriate reaction conditions involve a temperature greater than about 300° C. and a pressure greater than about 10 atm.