In situ extended x‐ray absorption fine structure spectroscopy of thin‐film nickel hydroxide electrodes

A convenient in situ electrochemical cell has been developed which permits x‐ray absorption measurements on thin‐film electrodes under electrochemical polarization. Extended x‐ray absorption fine structure spectra from highly disordered α‐Ni(OH)2 films, before and after polarization, provided quantitative results on the lattice contraction accompanying oxidation. Upon oxidation of α‐Ni(OH)2, the Ni‐O distance contracted from 2.05 to 1.86 A, and the Ni‐Ni distance contracted from 3.09 to 2.82 A. The observed 10% contraction in the brucite plane is consistent with the 3.67 nickel valence in a K(NiO2)3 phase. The present technique extends x‐ray absorption spectroscopy to the study of a variety of unstable materials not amenable to ex situ techniques.