 Sabatier's principle suggests that for hydrogen evolution, a plot of the rate constant versus the hydrogen adsorption energy should result in a volcano shape. However, this has not always been observed in the literature. When oxide-coated metals were removed from the equation, no volcano was seen. Factors such as the reaction passing through more suitable intermediate states and the orbitals of nickel being too compact to be a good catalyst were also considered. This article was authored by Palacuano, Fernanda Juarez, Elizabeth Santos, and others.