General Solution to a basis set describing the hydrogen evolution reaction and hydrogen occlusion
The presence of impurities on the surface of a metal have a marked effect on both the hydrogen evolution reaction (HER) and electrochemical insertion of hydrogen into the bulk.These effects are modeled using analytical forms for the Volmer (V), Heyrovsky (H), Tafel (T) and penetration/occlusion (P) reactions. Two techniques to simultaneously solve for the exchange current densities ( and symmetry coefficients for the V-H- T reaction routes are developed. These methods are then applied to a subset of palladium cathodes doped or codoped with Bi, Pb and Pt from our recent publications.
The results provide valuable insight into the competition between the V, H, and T reactions and their impact on hydrogen occlusion in palladium as a function of applied current density. Shown in figure, is the impact of use of either Tafel poisons or the combined use of Tafel poisons and Volmer promoters on the loading and specific power required to achieve a given bulk hydrogen loading level in palladium. While the use of just a Tafel poison has a marked improvement in loading vs specific power, the best solution maybe the combination of both a poison and a promoter.
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The results were submitted for publication in Thermochimica Acta Journal. Update will follow.