MICROCALORIMETRIC STUDY OF THE SELF-DISCHARGE OF THE NIOOH NI(OH)2 ELECTRODE IN A HYDROGEN ENVIRONMENT

A microcalorimetric method has been used to investigate the self-discharge behaviour of nickel oxyhydroxide electrodes in a pressurized gaseous hydrogen environment. It was found that the heat generation rate is proportional to hydrogen pressure, and is significantly dependent on the immersion state of the electrode in the electrolyte. Hence, diffusion of dissolved hydrogen gas towards or within the electrode controls, at least partially, the self-discharge rate. However, the heat generation decreases exponentially with time, indicating that self-discharge is also proportional to the amount of the charged active material available for the reaction. The presence of Mg, Co and Cd oxides or hydroxides appears to inhibit self-discharge. It was found that direct chemical reaction between dissolved hydrogen and the active material dominates, while in addition, electrochemical oxidation of hydrogen coupled with electrochemical reduction of the active material might also occur at a much smaller rate than the direct reaction.