INSITU TIME-RESOLVED EXAFS STUDY OF THE STRUCTURAL MODIFICATIONS OCCURRING IN NICKEL-OXIDE ELECTRODES BETWEEN THEIR FULLY OXIDIZED AND REDUCED STATES

In-situ time-resolved extended X-ray absorption fine structure (EXAFS) spectroscopy at the Ni K-edge was coupled with cyclic voltammetry to investigate the structural changes occurring in nickel hydroxide electrodes between their fully charged and discharged states. On the negative sweep, analysis of the EXAFS data indicated that the reduction process does not involve the formation of a new compound. The appearance of a second cathodic peak in the cyclic voltammogram is best explained as being due to the formation of an electronically insulating barrier surrounding the active material. On the positive sweep, a threshold potential difference between the onset of the anodic current and that of the electronic and structural modifications was observed. This is due to the fact that the oxidation of the incorporated OH- ions occurs prior to that of the Ni compound.