Mechanism and kinetics of interaction between gaseous oxygen and nickel oxide surfaces

Abstract

The interaction between gaseous oxygen and the surface of pure nickel oxide and NiO doped with Li₂O was studied by means of work function measurements. It was observed that at low oxygen pressures in measurements carried out with a constant amount of the gas in the reaction chamber, rather than carried out at constant pressure, at the temperatures corresponding to the adsorption equilibrium, the work function initially increased and then decreased. It was concluded that this complex character of the observed work function changes versus time is due to the superimposition of two parallel effects, i.e., charging of the NiO surface during oxygen chemisorption and simultaneous discharging of this surface by diffusion of ions from the bulk. On the basis of the electric model of the NiO surface covered with adsorbed oxygen, a quantitative interpretation of the above processes was proposed and a kinetic equation was given. The proposed kinetic equation was solved with the aid of an analog computer, and good agreement between the experimental curves and the kinetic equation was obtained.