Hydrogen Overpotential on Platinum

摘要

Hydrogen electrode kinetics have been examined in Pt in HCl solutions over a large range of anodic and cathodic current densities using several techniques (rotating disc-ring, cyclic linear sweep voltammetry, interrupter, and pulse techniques). Bubble formation was studied on the rotating disc electrode photographically. The experimental results support the following conclusions: (1) Under most anodic and cathodic conditions in concentrated acids, the hydrogen electrode on Pt is under combined H2-diffusion and kinetic control. (2) Both the discharge and oxidation of H2 on Pt proceed through the combination mechanism with the atomic-combination step rate controlling. Two types of absorbed hydrogen appear to be involved--one strong at high coverage and one weak at lower coverage. Thus: M- + H(+) + e(-) = M-HA; MHA = M-HB; 2M-HB = M- + H2 where M-HA is the more strongly bound hydrogen. (3) In well purified solutions, extreme supersaturation with dissolved H2 occurs during cathodic polarization at high currents densities. (4) Theoretical considerations reveal that the transfer coefficient or its equivalent for the recombination and ion-plus-atom steps are probably closer to unity than the usual value of 1/2. (Author)