University of California Los Angeles,
Keywords: oxygen reduction reaction, surface doping, PtNi alloy
Summary:Proton-exchange membrane (PEM) fuel cells use platinum (Pt) to catalyze reactions between the fuel (hydrogen, alcohols, etc.) at the anode and the oxidant (molecular oxygen) at the cathode. However the high cost of Pt, the sluggish kinetics of the oxygen reduction reaction (ORR), and the low durability of the catalysts have hindered further development. Bimetallic platinum-nickel (Pt-Ni) nanostructures represent an emerging class of electrocatalysts for oxygen reduction reaction (ORR) in fuel cells, but practical applications have been limited by catalytic activity and durability. To address these challenges, we surface doped Pt3Ni octahedra supported on carbon with transition metals, termed M‐Pt3Ni/C, where M represents a wide range of transition metals including vanadium, chromium, manganese, iron, cobalt, molybdenum (Mo), tungsten, or rhenium. Impressively the Mo‐Pt3Ni/C showed ORR performance with specific activity and mass activity that are nearly two order of magnitude higher than those of the commercial Pt/C catalyst. Most importantly these catalysts showed greatly enhanced stability retaining over 90% of the ECSA and initial activities after prolonged accelerated deterioration test. Theoretical calculations suggest Mo prefers subsurface positions near the particle edges in vacuum and surface vertex/edge sites in oxidizing conditions, where it enhances both the performance and the stability of the Pt3Ni catalyst. These studies our studies clearly demonstrate that by engineering the surface structure of the octahedral Pt3Ni nanocrystal, it is possible to fine-tune the chemical and electronic properties of the surface layer and hence modulate its catalytic activity. This approach may be broadly applied to engineer the surface of various catalysts for performance improvement.