Non-platinum group oxygen reduction reaction catalysts
Methods for producing non-platinum group metal electrocatalysts effective for the reduction of oxygen in fuel cells and other electrochemical reactions and electrocatalysts as may be produced by these methods are described. The electrocatalysts can be formed according to low to medium temperature formation methods and may be particularly attractive for use in low-temperature fuel cells.
1. A method for forming an electrocatalytic structure comprising:
forming an electrocatalyst, the method for forming the electrocatalyst including
reacting monomers in a melt at a reaction temperature, the melt comprising the monomers, a solvent, and a catalyst, wherein the catalyst and the solvent are a Lewis acid, the Lewis acid having a melting point below the reaction temperature, the Lewis acid being based on main group metals, early d-block metals, or late d-block metals, the reaction forming a three dimensional polymeric framework, the monomers including at least one π-conjugated moiety, the reaction forming linkages between individual monomers, at least a portion of the monomers and/or linkages providing at least one multidentate chelating site comprising multiple heteroaryl nitrogen atoms; and
complexing a metal ion within the framework at the chelating site via formation of coordinate bonds between the metal ion and the multiple heteroaryl nitrogen atoms of the chelating site, the metal ion comprising a non-platinum group metal capable of use as an active site in an oxygen reduction reaction.
2. The method of claim 1 , wherein the reaction is an ionothermal synthesis.
3. The method of claim 1 , the linkages comprising at least one heteroaryl group comprising phenazine ring linkages formed via a phenazine ring fusion reaction.
4. The method of claim 1 , the linkages comprising at least one heteroaryl group comprising triazine linkages formed via a cyano cyclotrimerization reaction.
5. The method of claim 1 , the linkages comprising an aryl group comprising benzene linkages formed via an alkynyl cyclotrimerization reaction.
6. The method of claim 1 , wherein at least a portion of the monomers comprises multiple heteroaryl nitrogen atoms, each of these heteroaryl nitrogen atoms being configured to form coordinate bonds with a metal ion such that these monomers provide at least one multidentate chelating site.
7. The method of claim 1 , the metal ion comprising a 3-d transition metal.
8. The method of claim 1 , wherein the reaction temperature is about 400° C. or less.
9. The method of claim 1 , further comprising combining the electrocatalyst with an electrode binder.
10. The method of claim 1 , further comprising locating the electrocatalyst in ionic communication with an ion-conducting electrolyte.
11. The method of claim 1 , further comprising locating the electrocatalyst in electrical communication with an electrode current collector.
12. The method of claim 1 , the non-platinum group metal comprising iron, cobalt, copper, nickel, chromium, manganese, or combinations thereof.
13. The method of claim 10 , further comprising locating the ion-conducting electrolyte in ionic communication with
an electrode, the ion-conducting electrolyte electrically isolating the electrode and the electrocatalyst.
14. The method of claim 10 , wherein the ion-conducting electrolyte is a proton-conducting electrolyte or a hydroxyl ion-conducting electrolyte.
15. The method of claim 10 , wherein the ion conducting electrolyte comprises an ion-conducting membrane.
16. The method of claim 1 , wherein the reaction temperature is about 300° C. or less.
17. The method of claim 1 , wherein the Lewis acid is based on aluminum, boron, silicon, tin, titanium, zirconium, iron, copper, or zinc.
18. The method of claim 1 , wherein the Lewis acid comprises zinc chloride, iron chloride, or aluminum chloride.
19. A method for forming an electrocatalytic structure comprising:
forming an electrocatalyst, the method for forming the electrocatalyst including
reacting monomers in a melt in the presence of a Lewis acid catalyst to form a three dimensional polymeric framework, the monomers including at least one π-conjugated moiety, the reaction forming linkages between individual monomers, at least a portion of the monomers and/or linkages providing at least one multidentate chelating site comprising multiple heteroaryl nitrogen atoms; and
complexing a metal ion within the framework at the chelating site via formation of coordinate bonds between the metal ion and the multiple heteroaryl nitrogen atoms of the chelating site, the metal ion comprising a non-platinum group metal capable of use as an active site in an oxygen reduction reaction; wherein
the reaction temperature is about 300° C. or less.
20. The method of claim 19 , the linkages comprising phenazine ring linkages, triazine linkages or benzene linkages.
21. The method of claim 19 , the non-platinum group metal comprising iron, cobalt, copper, nickel, chromium, manganese, or combinations thereof.
22. The method of claim 19 , further comprising combining the electrocatalyst with an electrode binder.
23. The method of claim 19 , further comprising locating the electrocatalyst in ionic communication with an ion-conducting electrolyte.
24. The method of claim 19 , further comprising locating the electrocatalyst in electrical communication with an electrode current collector.