Electrochemical and In Situ Raman Spectroscopic Characterization of Nickel Hydroxide Electrodes: I. Pure Nickel Hydroxide

Abstract

In situ laser Raman spectra of electrochemically precipitated thin‐film electrodes in alkaline NaOH electrolytes were recorded, and the effect of repeated charge‐discharge cycling on the structure and phase composition of the discharged and charged films was investigated. Careful deconvolution analyses of the Raman and surface‐enhanced Raman spectra showed that freshly precipitated films of contain not only an α‐like phase but also small amounts of a β‐phase. By combining cyclic voltammetry with in situ Raman spectroscopy, spectral changes that accompanied charge‐discharge cycling could be associated with a partial transformation of the predominant α‐phase into a disordered β‐ phase. A new phase characterized by a vibration at 522 cm ⁻¹ was also discovered in the film at the end of the cycling procedure. Analysis of the Raman spectra of the oxidized electrode (NiOOH active material) revealed for the first time a slight variation of the 477/559 cm⁻¹ peak pair ratio, which corresponds to phase transitions in the Ni(III) hydrous oxide film, as the electrode was cycled. Significant differences between the low‐frequency‐region Raman spectra of chemically synthesized α,β‐ and those of highly disordered hydrous films, as well as the absence of characteristic vibrations in the OH stretching region of the in situ Raman spectra of the electrode, suggest that chemically prepared α,β‐nickel hydroxides should not be regarded as structural models for electrochemically precipitated thin‐film materials.