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 Å, and the Ni-Ni distance contracted from 3.09 to 2.82 Å. 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.