In Situ 57Fe Mössbauer Spectroscopy Study of the Electrochemical Behavior of an Iron‐Substituted Nickel Hydroxide Electrode

The electrochemical cycling of a hydrated, iron‐substituted nickel hydroxide (20 atomic percent of iron substituted for nickel) in a Ni//Cd cell was studied in situ by Mössbauer spectroscopy. The variations of the iron oxidation state (and spin configuration) were followed throughout the discharge and correlated to the changes of the overall distribution of cationic oxidation states, as well as to the structural modifications. The charge starting from an α‐phase leads to a pure γ oxyhydroxide containing , and average valence ions. During the discharge, the evolution of the various cationic populations deduced from the Mössbauer data provides evidence of a γ‐type solid solution domain, in which the ions are reduced to the trivalent state rather than the iron ions, followed by γ + α biphased domain.