Studies of the thermal decomposition of βNiO(OH) and nickel peroxide by X-ray photoelectron spectroscopy

Abstract

The thermal decomposition of both βNiO(OH) and ‘nickel peroxide’ have been studied by combining X-ray photoelectron spectroscopic (X.p.s.) studies of the solid with mass-spectrometric analysis of the gas phase. Through monitoring the O(1s) and Ni(2p) spectra of the as-prepared solids during decomposition, with simultaneous analysis of the gas phase, it has been established that ‘nickel peroxide’ behaves in an identical fashion to βNiO(OH). We conclude that the two solids are chemically identical; on the other hand previous studies of ‘nickel peroxide’ have suggested it to be a hydrated defective oxide Ni₂O₃. Central to our argument is the observation that both solids exhibit initially a single O(1s) peak at 530.5 eV, but during decomposition this peak splits into two components, one at 529.7 eV and the other at 531.4 eV. It is suggested that intercalated water within the βNiO(OH) structure results in the equivalence (by X.p.s.) of the ‘oxygen species’ through the stabilisation of ‘OHO’ groups. Water and molecular oxygen are the predominant gaseous decomposition products, the solid, at 773 K, being converted into defective NiO.