The reduction of p-nitroaniline (PNA) by electrocatalytic hydrogenation (ECH) as well as the evolution and adsorption of hydrogen were found to be depressed by the formation of irreducible beta-Ni(OH)(2) or NiO at nickel-deposited graphite (Ni/C) electrodes. An increase In the Tafel slope from 120 to 200 mV dec(-1) in the low overpotential region of the hydrogen evolution reaction (HER) suggested that : (i) the HER mechanism on beta-Ni(OH)(2)/NiO is different from the Volmer-Heyrovsky-Tafel reactions or (ii) the reduction of these oxides predominates in this potential range. X-ray diffraction (XRD) results revealed that NiO was formed on the Ni/C electrode surface after it had been annealed in air at 400 degrees C for Ih. High-performance liquid chromatography (HPLC) results revealed that on the Ni/C electrodes before and after annealing treatment and on the pure Pt electrode, p-phenylenediamine (PPDA) is one of the major products in the PNA reduction and the selectivity of PPDA formation is the highest on pure Pt.