Hydrogen Overvoltage and Electrode Material. A Theoretical Analysis

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Abstract
It is shown on a theoretical basis that the overvoltage for hydrogen evolution on various metals and for otherwise identical conditions of electrolysis is essentially a linear function of the heat of adsorption of atomic hydrogen on the electrode. This relationship is deduced on the assumptions that the effect of the backward electrode reaction—the oxidation of hydrogen—can be neglected, and that the current is controlled by the discharge of hydrogen ions. This is the case for overvoltages larger than 0.1—0.15 volt. The relationship between overvoltage and heat of adsorption is tested for metals for which reliable overvoltage data are available, that is for Ag, Be, Cd, Cr, Cu, Fe, Ga, Hg, In, Ni, Pb, Tl. The argument is based on a kinetic equation for hydrogen overvoltage and on the use of potential energy curves for the initial and final states. These curves are determined from spectroscopic data. Heats of adsorption of atomic hydrogen are calculated by assuming the additivity of the M–M and H–H bond energies. Calculated heats of adsorption are listed for 25 metals. It is also shown that there is no correlation between hydrogen overvoltage for various metals and the electronic work function of these metals.

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