Abstract
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 β-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 β-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 °C for 1 h. 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. © 1998 Elsevier Science Ltd. All rights reserved.