Potential-induced plastic deformations of nickel hydrous electrodes in alkaline electrolytes: An in situ atomic force microscopy study

Dimensional changes of α-type nickel hydrous oxide, α-Ni(OH)₂(hyd), films electrodeposited on the basal plane of highly oriented pyrolytic graphite, HOPG(bp), electrodes, have been monitored by in situ by atomic force microscopy (AFM) in 1 M KOH as a function of the applied potential. Freshly prepared α-Ni(OH)₂-(hyd) films were found to consist of conformal sections covered by large numbers of distinctly bright, globular-type features (0.25 μm average diameter), separated by sharply defined crevices. Upon oxidation, the width of the crevices, W_c, increased, whereas the distances between any two globular features, i and j, within a specific section, r_ij, decreased. A statistical analysis involving more than 100 pairs of features from different sections of independent films showed that the relative decrease in r_ij, induced by the nominal full oxidation of the film, r_ij(ox)/r_ij(red), is remarkably constant, 0.06 ± 0.01, and independent of the magnitude of r_ij. Plots of W_c obtained from linear AFM scans along an axis normal to the crevice as a function of the extent of oxidation of the films revealed, within the time scale of the experiments, a marked hysteresis between the oxidation and subsequent reduction process.