SummarySabatier’s principle suggests, that for hydrogen evolution a plot of the rate constant versus the hydrogen adsorption energy should result in a volcano, and several such plots have been presented in the literature. A thorough examination of the data shows, that there is no volcano once the oxide-covered metals are left out. We examine the factors that govern the reaction rate in the light of our own theory and conclude, that Sabatier’s principle is only one of several factors that determine the rate. With the exception of nickel and cobalt, the reaction rate does not decrease for highly exothermic hydrogen adsorption as predicted, because the reaction passes through more suitable intermediate states. The case of nickel is given special attention; since it is a 3d metal, its orbitals are compact and the overlap with hydrogen is too low to make it a good catalyst.

We show how a theory for electrocatalysis developed in our group can be combined with density-functional theory in order to obtain free-energy surfaces for electrochemical reactions. The combined theory is applied to the first step in the hydrogen evolution reaction, which is a proton transfer from an electrolyte solution to a metal electrode. Explicit calculations have been performed for five metals: Pt, Au, Ag, Cu, and Cd. In accord with experimental findings we find a high activation energy for Cd, medium values for the coin metals, and on Pt the transfer occurs with little activation. These results are explained in terms of the position of the d band of these metals and their interactions with the hydrogen 1s orbital as the latter passes the Fermi level in the presence of the solvent.

Density functional theory (DFT) by itself is insufficient to model electrochemical reactions, because the interface is too large, and there is no satisfactory way to incorporate the electrode potential. In our group we have developed a theory of electrocatalysis, which combines DFT with our model for electrochemical electron transfer, and thereby avoids these difficulties. Our theory explains how a metal d band situated near the Fermi level can lower the energy of activation for a charge transfer reaction. An explicit application to the hydrogen evolution reaction gives results that agree very well with experimental data obtained both on plain and on nanostructured electrodes. Finally, we outline how our method can be extended to other reactions and present first results for the adsorption of OH on Pt(111).

The two faces of gold: the reduction of oxygen on gold electrodes in alkaline solutions has been investigated theoretically. The most favorable reaction leads directly to adsorbed O(2)(-), but the activation energy for a two-step pathway, in which the first step is an outer-sphere electron transfer to give solvated O(2)(-), is only slightly higher. d-band catalysis, which dominates oxygen reduction in acid media, plays no role. The reason why the reaction is slow in acid media is also explained.

We investigate hydrogen evolution on plain and nanostructured electrodes with a theory developed by us. On electrodes involving transition metals the most strongly adsorbed hydrogen is often only a spectator, while the reaction proceeds via a weakly adsorbed species. For Pt(111) the isotherms for both species are calculated. We explain why a nanostructure consisting of a monolayer of Pd on Au(111) is a good catalysts, and predict that Rh/Au(111) should be even better. Our calculations for a fair number of metals are in good agreement with experiment.