In relation to previous studies on the adsorption behavior of overpotential‐deposited (opd) H in the evolution reaction (HER) at active Pt electrodes, evaluated by means of analysis of potential‐decay transients, results of comparative experiments on electrodes of Pd and electrodeposited are reported. In particular, information is sought on the role of H in the hydride phase at Pd‐containing electrodes on the behavior of the HER and its comparative relation to apparent H sorption effects at active Pt electrodes in acidic solutions. Experiments were conducted at rotated electrodes (4900 rpm) in order to avoid effects that can arise at active electrode surfaces from supersaturation of electro‐generated in a boundary layer at the electrode surface. The behavior of opd H at the Pd electrode is shown to be quite similar to that at active Pt electrodes in acid solution and to be substantially influenced by the H sorbed in Pd as the phase. By analogy, support is given to formation of a hydride phase at active Pt electrodes in the near surface‐region of the electrode at its interface with the solution. The opd H at Pd is characterized from the potential‐decay experiments in terms of two regions of the decay transients and evaluation of the corresponding capacitances: the double layer capacitance at short times and, further, the much larger H‐pseudo‐capacitance that determines the longer time decay behavior. Behavior in acid and alkaline solutions is compared.
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Elam et al. (1988) studied this question.