Proton Tunneling in the Hydrogen‐Evolution Reaction

The quantum‐mechanical theory of tunneling was applied to the proton‐discharge step of the hydrogen‐evolution reaction. An unsymmetric Eckart barrier with allowance for zero‐point energies was employed. The quantum‐mechanical rate iq was calculated by integration with a digital computer for a large number of combinations of barrier width, barrier heights, heats of reaction, and temperatures over a large potential range for protium, deuterium, and tritium. From these results the quantum‐mechanical transmission coefficient τ and the quantum‐mechanical correction Γ to the separation factor, Tafel slopes, and activation energies were calculated. By comparison to observed values of SH,T, and SH,T as a function of temperature and potential the most probable barrier parameters were obtained. These values were tested by comparison of calculated and observed activation energy, Tafel slopes, SH,D as a function of potential, and the rate of protium evolution at high cathodic overpotentials as a function of temperatu...

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