Structural defects and electrochemical reactivity of β-Ni(OH) 2

Abstract

Electrochemical reactivities and structural properties of several nickel hydroxide powders were analysed by X-ray diffraction, Raman spectroscopy and extended X-ray absorption fine structure (EXAFS). It is shown that the electrochemical efficiency of β-Ni(OH) 2 is associated with the amount of proton vacancies included in the crystal lattice. The number of those proton vacancies increases when the crystallite size decreases or when the ratio of co-precipitated cobalt increases. Proton vacancies shift the oxidation potential of β-Ni(OH) 2 towards less anodic values and, therefore, improve the chargeability and the electrochemical efficiency of nickel hydroxide. It is shown that both Raman spectroscopy and X-ray diffraction techniques can be used to predict effectively the electrochemical efficiency of β-Ni(OH) 2 hydroxide. EXAFS results indicate also that the oxidation level of nickel atoms inside the hydroxide is not modified by the existence of proton vacancies. It means probably that to maintain the electroneutrality in the whole crystal induces others singularities. Finally, the influence of co-precipitated additives such as cadmium and cobalt on the rate of defects has been investigated.