The lifetime of an AMTEC electrode is predicted from the rate of grain growth in the electrode. The rate of growth depends on several physical characteristics of each material, including the rate of diffusion of the material on itself. Grain growth rates for rhodium-tungsten and titanium nitride electrodes have been determined, and have been used to predict operating lifetimes of AMTEC electrodes. For lifetimes of 10 years or more, RhxW electrodes may be used at any operating temperature supportable by the electrolyte. TiN electrodes may be used in AMTEC cells only at operating temperatures under 1150 K.