KINETICS OF THE DEUTERIUM AND HYDROGEN EVOLUTION REACTIONS AT PALLADIUM IN ALKALINE-SOLUTION

The kinetics of the deuterium evolution reaction (DER) at palladium in alkaline solution were investigated by measuring the overpotential de cay transients arising from interruption of the polarising current. It was found that the overpotential eta could be time-resolved into two separate components. The initial component eta(1) arises from the Volm er reaction, while the longer-lived component eta(2) is attributed to the Tafel reaction. The Volmer-Tafel mechanism was also confirmed by e xamining the dependence of eta(2) on eta, although there were some ind ications that, at high overpotentials, the Heyrovsky reaction is also involved. Studies of the hydrogen evolution reaction (HER) at palladiu m were also consistent with a Volmer-Tafel process. The rates of the V olmer and Tafel reactions were found to be higher for the HER than the DER, in agreement with known electrolytic H/D separation factors. Mea surements of eta(2) were used to estimate the stoichiometry of the deu terated palladium cathode using the concept of equivalent D-2 pressure . The D/Pd loading ratios were found to increase with current density, reaching values of between 0.78 and 0.82 at 50 mA cm(-2).