THE ADSORBED INTERMEDIATE OF THE HYDROGEN EVOLUTION REACTION AT PT IN ACID-SOLUTION

The rotating-disc electrode-potential-step coulometry (RDE-PSC) method was extended to the study of those cases in which the surface concentration c(s)* of soluble intermediate or product depends only on the rate of electron transfer. In the potential range where the steady-state current does not vary with the rotation speed, the quantity of electricity Q(s) involved in the reaction of soluble intermediate or product is proportional to the inverse of the angular velocity of rotation omega--1. When this method was applied to the study of the adsorbed intermediate of the hydrogen evolution reaction (HER) at Pt in acid solution, it was found that the charge Q(Had) of hydrogen electrosorption increases continuously from the underpotential deposition (UDP) region to the HER region. It seems to indicate that the reactive intermediate in the HER is different from the underpotential deposited hydrogen.