Active sites for the hydrogen oxidation and the hydrogen evolution reactions on the high index planes of Pt

Structural effects on the hydrogen oxidation reactions (HOR) and the hydrogen evolution reactions (HER) have been studied on (n-1)(1 1 1)-(1 1 0), n(1 0 0)-(1 1 1), n(1 0 0)-(1 1 0) and n(1 1 1)-(1 0 0) series of Pt using rotating disk electrode (RDE) in 0.1 M HClO(4) saturated with H(2). The value of the exchange current density J(0) increases linearly with the increase of the step atom density d(S) from n = infinity to n = 9, where n denotes the number of terrace atomic rows, on (n-1)(1 1 1)-(1 1 0), n(1 0 0)-(1 1 1), and n(1 0 0)-(1 1 0) series. This indicates that the activity for the HOR/HER of the step is higher than that of the terrace. The values of j(0) of (n-1)(1 1 1)-(1 1 0), n(1 0 0)-(1 1 1) and n(1 0 0)-(1 1 0) series become constant on the surfaces with n <= 9, whereas those of n(1 1 1)-(1 0 0) series increase with the increase of d(S). The activity for the HOR/HER per step atom increases in the sequence: n(1 1 1)-(1 0 0) < n(1 0 0)-(1 1 1) < n(1 0 0)-(1 1 0) < (n-1)(1 1 1)-(1 1 0). This result supports that the most active site for the HOR/HER is the linear (1 1 0) step. Decrease of the NOR current is found around 0.2 V(RHE) on the surfaces with (1 0 0) terrace, whereas the surfaces with (1 1 1) terrace give no decrease of the HOR current. (C) 2011 Elsevier B.V. All rights reserved.