Evidence from photoelectron spectroscopy for dissociative adsorption of oxygen on nickel oxide

XPS and UPS spectra from oxygen adsorption at high temperature on polycrystalline nickel oxide surfaces pre-heated at 700°C and 1450°C are presented. Adsorption results in complete loss of surface charge on both surfaces. There is an increase in intensity of the 0(1s) 529.7 eV peak, attributed to O^2? ions, and the $\text{Ni}\text{(2p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{)}$ spectra show a shift of intensity to the 854.6 eV peak due to Ni²⁺ ions. The results are compared with previous data from kinetic, conductivity and electrochemical measurements. Agreement with a model of O^2? and nickel vacancy production is demonstrated. UPS spectra indicate considerable reorganisation of electronic charge in the surface of the 1450°C pre-heated oxide, after oxygen adsorption, giving an almost stoichiometric surface similar to that of a cleaved single crystal.