Analysis of the Charge-Discharge Characteristics of Nickel-Oxide Electrodes by Infrared Spectroscopy

Abstract

Infrared spectroscopy is shown to be a sensitive tool in studies of the structure of electrochemically active materials and in elucidating the mechanism of charge and discharge. The spectrum of the sintered nickel‐oxide electrode, impregnated using standard procedures, has been determined in the region between 4000 and 250 cm⁻¹. These spectral data show the discharged state to be having a hexagonal layer structure isomorphic with the space group . The hydroxyl groups are parallel to the c‐axis of the crystal and are “free” in the sense that hydrogen bonding is absent. Associated with this structure is a relatively small amount of water which is trapped in the crystal lattice through the formation of coordinate‐covalent bonds with the nickel ions. The charging process is accompanied by the formation of a hydrogen‐bonded structure possessing a higher degree of crystal symmetry than is found in the discharged state. During discharge, these hydrogen bonds are continuously broken, and the structure transforms back to a free hydroxyl configuration.