Catalyst
Nanoporous oxygen reduction catalyst material comprising at least 90 collectively Pt, Ni, and Ta. The nanoporous oxygen reduction catalyst material is useful, for example, in fuel cell membrane electrode assemblies.
1. A nanoporous oxygen reduction catalyst material comprising at least 90 atomic percent collectively Pt, Ni, and Ta,
wherein the nanoporous oxygen reduction catalyst material is in the form of at least one nanoporous layer comprising platinum and nickel,
wherein there is a layer comprising tantalum on at least one of the nanoporous layers comprising platinum and nickel,
wherein the tantalum is metallic or in an oxide phase, and
wherein the nanoporous oxygen reduction catalyst material comprises in a range from 52.7 to 61.9 atomic percent Pt, in a range from 34.4 to 43.3 atomic percent Ni, and in a range from 0.2 to 10.5 atomic percent Ta, wherein the total atomic percent of Pt, Ni, and Ta equals 100.
2. The nanoporous oxygen reduction catalyst material of claim 1 having pores with diameters in a range from 1 nm to 10 nm.
3. The nanoporous oxygen reduction catalyst material of claim 1 comprising in a range from 52.7 to 59.6 atomic percent Pt, in a range from 34.4 to 43.3 atomic percent Ni, and in a range from 0.3 to 10.5 atomic percent Ta, wherein the total atomic percent of Pt, Ni, and Ta equals 100.
4. The nanoporous oxygen reduction catalyst material of claim 1 , wherein the layer comprising tantalum has a planar equivalent thickness up to 50 nm.
5. The nanoporous oxygen reduction catalyst material of claim 1 having an exposed tantalum surface layer.
6. The nanoporous oxygen reduction catalyst material of claim 5 , wherein the exposed tantalum surface layer is a sub-monolayer of tantalum.
7. The nanoporous oxygen reduction catalyst material of claim 1 , wherein the weight ratio of platinum to tantalum is in a range from 2:1 to 250:1.
8. A catalyst comprising nanostructured elements comprising microstructured support whiskers having an outer surface at least partially covered by the nanoporous oxygen reduction catalyst material of claim 1 .
9. A fuel cell membrane electrode assembly comprising the catalyst of claim 8 .
10. A method comprising:
providing an oxygen reduction catalyst material comprising Pt, Ni, and Ta, wherein there are layers comprising platinum and nickel; and
dealloying at least some layers comprising platinum and nickel to remove at least a portion of the nickel from at least one layer to provide the nanoporous oxygen reduction catalyst material of claim 1 .
11. The method of claim 10 , further comprising annealing the catalyst before dealloying.
12. The method of claim 10 , wherein the weight ratio of platinum to tantalum prior to dealloying is in a range from 6:1 to 329:1.
13. The method of any of claim 10 , wherein the atomic ratio of platinum to nickel prior to dealloying is in a range from 0.05:1 to 0.43:1.