Structural effects on the oxygen reduction reaction on the high index planes of Pt3Ni: n(1 1 1)–(1 1 1) and n(1 1 1)–(1 0 0) surfaces

•The ORR activity decreases with the increase of step atom density on n(1 1 1)–(1 1 1) surfaces of Pt3Ni.•This tendency is completely opposite to that on n(1 1 1)–(1 1 1) surfaces of Pt.•On n(1 1 1)–(1 0 0) surfaces of Pt3Ni, 3 and 5 atomic rows of terrace forms the most active sites.

Active sites for the oxygen reduction reaction (ORR) have been studied on n(1 1 1)–(1 1 1) and n(1 1 1)–(1 0 0) surfaces of Pt3Ni in 0.1 M HClO4 using rotating disk electrode (RDE). The activity for the ORR is decreased with the increase of the step atom density on n(1 1 1)–(1 1 1) surfaces. This fact is completely opposite to that of the same series of Pt on which the activity is enhanced at higher step atom density. The ORR gives the highest activity on n(1 1 1)–(1 0 0) surfaces of Pt3Ni with terrace atomic rows n = 3 and n = 5. These results show that the activity for the ORR of (1 0 0) step is superior to that of (1 1 1) step on Pt3Ni electrodes.