The electrochemical behavior of a sputtered film of carbon and nickel, of approximate stoichiometry NiC3, is presented. This film is quite passive in hot sulfuric acid solution. The material also displays considerable electrocatalytic activity toward the hydrogen reaction, both anodically and cathodically. The electrocatalyst is passivated by the carbon component after dissolution of some of the surface nickel. The remaining surface nickel, entrapped by carbon, provides electrocatalytic activity comparable with that of pure polycrystalline nickel. (c) 2008 The Electrochemical Society.