Synthesis and characterization of 9 nm Pt-Ni octahedra with a record high activity of 3.3 A/mg_Pt for the oxygen reduction reaction

Nanoscale Pt-Ni bimetallic octahedra with controlled sizes have been actively explored in recent years owning to their outstanding activity for the oxygen reduction reaction (ORR). Here we report the synthesis of uniform 9 nm Pt-Ni octahedra with the use of oleylamine and oleic acid as surfactants and W(CO)₆ as a source of CO that can promote the formation of {111} facets in the presence of Ni. Through the introduction of benzyl ether as a solvent, the coverage of both surfactants on the surface of resultant Pt-Ni octahedra was significantly reduced while the octahedral shape was still attained. By further removing the surfactants through acetic acid treatment, we observed a specific activity 51-fold higher than that of the state-of-the-art Pt/C catalyst for the ORR at 0.93 V, together with a record high mass activity of 3.3 A mg_Pt^-1 at 0.9 V (the highest mass activity reported in the literature was 1.45 A mg_Pt^-1). Our analysis suggests that this great enhancement of ORR activity could be attributed to the presence of a clean, well-preserved (111) surface for the Pt-Ni octahedra.