Noble metal-based electrocatalyst and method of treating a noble metal-based electrocatalyst
A noble metal-based electrocatalyst comprises a bimetallic particle comprising a noble metal and a non-noble metal and having a polyhedral shape. The bimetallic particle comprises a surface-segregated composition where an atomic ratio of the noble metal to the non-noble metal is higher in a surface region and in a core region than in a sub-surface region between the surface and core regions. A method of treating a noble metal-based electrocatalyst comprises annealing a bimetallic particle comprising a noble metal and a non-noble metal and having a polyhedral shape at a temperature in the range of from about 100° C. to about 1100° C.
1. A method of treating a noble metal-based electrocatalyst, the method comprising:
annealing a bimetallic particle comprising a noble metal and a non-noble metal and having a polyhedral shape at a temperature in a range from about 100° C. to about 1100° C.,
wherein the annealing induces a surface-segregated composition in the bimetallic particle where an atomic ratio of the noble metal to the non-noble metal is higher in a surface region and in a core region than in a sub-surface region therebetween,
wherein, after the annealing, the bimetallic particle consists essentially of the surface region, the core region, and the sub-surface region.
2. The method of claim 1 , wherein the annealing is carried out in a vacuum environment of about 10 −3 Pa or lower.
3. The method of claim 1 , wherein the annealing is carried out in an inert gas environment.
4. The method of claim 1 , wherein the temperature is in the range from about 100° C. to about 700° C.
5. The method of claim 1 , wherein the annealing has a duration from about 20 minutes to about 2 hours.
6. The method of claim 1 , further comprising exposing the bimetallic particle to an electrochemical treatment.
7. The method of claim 6 , wherein the electrochemical treatment comprises a multi-cycle oxygen reduction reaction (ORR) measurement.
8. The method of claim 7 , wherein the bimetallic particle is exposed to the ORR measurement for 10 to 30 cycles.
9. The method of claim 1 , wherein the noble metal is selected from the group consisting of: Pt, Pd, Au, Ag, Ru, Rh, Os, and Ir, and wherein the non-noble metal is selected from the group consisting of: Ti, V, Cr, Mn, Mo, Zr, Nb, Ta, Zn, In, Sn, Sb, Pb, W, Co, Cu, Ni and Fe.
10. The method of claim 9 , wherein the noble metal comprises Pt and the non-noble metal comprises Ni.
11. The method of claim 1 , wherein the bimetallic particle comprises a polyhedral shape selected from the group consisting of: cube, truncated octahedron, octahedron, truncated tetrahedron, tetrahedron, and icosahedron.
12. The method of claim 1 , wherein the bimetallic particle is attached to a support.
13. The method of claim 12 , wherein the support is a carbon support.
14. The method of claim 1 , wherein, after the annealing, the bimetallic particle exhibits an ORR activity of at least about 0.5 mA per microgram of the noble metal.
15. The method of claim 1 , wherein the core region has a size of from about 40% to about 60% of a size of the bimetallic particle, wherein the surface region has a thickness of from about 10% to about 30% of the size of the bimetallic particle, and wherein the sub-surface region has a thickness of from about 10% to about 50% of the size of the bimetallic particle.