EFFECTS OF THE NICKEL-OXIDE ON THE HYDROGEN EVOLUTION AND PARA-NITROANILINE REDUCTION AT NI-DEPOSITED GRAPHITE-ELECTRODES IN NAOH

The reduction of p-nitroaniline (PNA) by electrocatalytic hydrogenatio n (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 Ta fel slope from 120 to 200 mV dec(-1) in the low overpotential region o f the hydrogen evolution reaction (HER) suggested that: (i) the HER me chanism on beta-Ni(OH)(2)/NiO is different from the Volmer-Heyrovsky-T afel reactions or (ii) the reduction of these oxides predominates in t his potential range. X-ray diffraction (XRD) results revealed that NiO was formed on the Ni/C electrode surface after it had been annealed i n air at 400 degrees C for Ih. High-performance liquid chromatography (HPLC) results revealed that on the Ni/C electrodes before and after a nnealing treatment and on the pure Pt electrode, p-phenylenediamine (P PDA) is one of the major products in the PNA reduction and the selecti vity of PPDA formation is the highest on pure Pt. (C) 1998 Elsevier Sc ience Ltd. All rights reserved.