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 voltarnmetry. The surfaces examined are Pd(S)-[n(100) x (110)], Pd(S)-[n(111) x (100)] and Pd(S)-[n(111) x (111)] series (n=2-9). The results are compared with those of Pd(S)-[n(100) x (111)] series reported previously. All the electrodes give maximum currents of formic acid oxidation j(p) between 0.5 and 0.8 V (RHE). The values of j(p) plotted against the density of step (kink) atoms d(s) depend on the surface structure remarkably. Pd(S)-[n(111) x (100)] surfaces provide maximum of j(p) at n=5, whereas Pd(S)-[n(100) x (110)] and Pd(S)-[n(111) x (111)] do not give maximum of j(p). The values of j(p) have the following order: Pd(S)[n(111)x(111)]< Pd(S)-[n(111)x(100)]< Pd(S)-[n(100)x(110)]< Pd(S)-[n(100)x(111)]. The anodic current at more negative potential 0.20 V (RHE) shows different activity series: Pd(111) and Pd(110) have the highest rate for formic acid oxidation at 0.20 V (RHE). (c) 2006 Elsevier B.V. All rights reserved.