Kinetics of the hydrogen-evolution reaction on palladium electrodes in molten potassium bisulphate

Abstract

The kinetics of the electrochemical formation of hydrogen on differently prepared prepared palladium electrodes in the electrolysis of molten potassium bisulphate has been studied in the temperature range 240 to 330°C. Current/voltage curves fit two limiting Tafel lines having slopes of 2·3(RT/2F) and 2·3(2RT/F) respectively. Semilogarithmic plots of decay curves exhibit a limiting region of slope 2·3(RT/2F). At high temperature an interference due to permeation of hydrogen in the metal during the decay process is observed, particularly noticeable when bright palladium electrodes are used. The kinetics of the electrochemical process is interpreted, on the basis that the α-Pd-H system predominates, the rate-determining step being the combination of hydrogen atoms on the electrode surface, at least at low overvoltages. At higher ones the ion-plus-atom reaction can account for the experimental results.