Oxygen chemisorption on doped nickel oxide and related conductivity changes

Abstract

The chemisorption of O₂on NiO doped with Li₂O and Cr₂O₃has been studied in the temperature range 250–350°C. The uptake and the d.c. conductivity changes occurring during the adsorption were measured simultaneously and recorded continuously. Pressure changes were followed in a constant volume apparatus by a self-balancing Pirani gauge, and the conductivity changes were determined using a novel electrode assembly. The rate of adsorption of O₂on NiO samples could not be described by a single process although more than half of the uptake was accounted for by Elovich-type kinetics. Doping affected the activation energies of adsorption and other kinetic parameters; total coverage was increased by both Li- and Cr-doping. Samples were characterized by determinations of a.c. conductivity, magnetic susceptibility, surface area and X-ray structure.