Extended Hückel calculations on hydrogen evolution at metal surfaces
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It has been found that an approximately linear relationship exists between the mechanism of H2 evolution concerning overvoltage and the heats of adsorption of atomic hydrogen on various metals. The reaction under consideration is M27H[Superscript z over subscript 2]--> M[Superscript z over subscript 27] + H2 were Z represents the charge on the metal slab. Extended Hückel calculations have been carried out to gain a greater insight into this correlation. Some factors that have been considered are the location of the hydrogen atoms on the surface, charge on the metal surface, and the coverage of hydrogen atoms on the metal surface. The change in the metal - hydrogen overlap population, as well as the hydrogen - hydrogen overlap population, has been studied with varying charges. Density of states (DOS) plots have also been used to understand the surface interactions between the metal and hydrogen. The mechanism of chemical - desorption was taken as the basis of the reaction. When a maximum in the hydrogen - hydrogen overlap population is found for this system by varying the charge, it was found that the charge estimates the overvoltage, and to a lesser degree that the metal - hydrogen overlap estimates the heat of adsorption. Results were found for cadmium, silver, copper, nickel, and platinum.