Elementary mechanisms of electrochemical reactions that take place over solid oxide fuel cell electrodes are not well understood. We present a first-principles approach, combining density functional theory calculations and statistical thermodynamics, aimed at studying electrochemical surface reactions. We have utilized this approach to investigate a mechanism for the electrochemical oxidation of hydrogen on various metal surfaces under solid oxide fuel cell operating conditions. Our analysis shows that oxygen adsorption energy is an excellent descriptor for the electrocatalytic activity of different metals. We demonstrate that the electrochemical activity of metals, as a function of the oxygen adsorption energy, can be described with a volcano plot where weak oxygen-metal binding results in a high anode overpotential loss while highly exothermic interactions of oxygen and a metal surface result in the oxygen-induced poisoning of the electrocatalyst. The observed volcano plots are consistent with experimental observations. (C) 2007 The Electrochemical Society.