Structural effects on the oxidation of formic acid on the high index planes of palladium

Electrochemical oxidation of formic acid has been studied on the stepped and kinked-stepped surfaces of Pd in 0.1 M HClO4 containing 0.1 M formic acid with the use of voltammetry. The surfaces examined are Pd(S)-[n(1 0 0) × (1 1 0)], Pd(S)-[n(1 1 1) × (1 0 0)] and Pd(S)-[n(1 1 1) × (1 1 1)] series (n = 2–9). The results are compared with those of Pd(S)-[n(1 0 0) × (1 1 1)] series reported previously. All the electrodes give maximum currents of formic acid oxidation jP between 0.5 and 0.8 V (RHE). The values of jP plotted against the density of step (kink) atoms dS depend on the surface structure remarkably. Pd(S)-[n(1 1 1) × (1 0 0)] surfaces provide maximum of jP at n = 5, whereas Pd(S)-[n(1 0 0) × (1 1 0)] and Pd(S)-[n(1 1 1) × (1 1 1)] do not give maximum of jP. The values of jP have the following order: Pd(S)-[n(1 1 1) × (1 1 1)] < Pd(S)-[n(1 1 1) × (1 0 0)] < Pd(S)-[n(1 0 0) × (1 1 0)] < Pd(S)-[n(1 0 0) × (1 1 1)]. The anodic current at more negative potential 0.20 V (RHE) shows different activity series: Pd(1 1 1) and Pd(1 1 0) have the highest rate for formic acid oxidation at 0.20 V (RHE).