Metal hydride foils can serve as support structures for electronically insulating proton conductors to afford metal hydride-barrier composite electrolytes operating at temperatures in between molten carbonate fuel cells and phosphoric acid fuel cells. In addition, such barrier electrolytes entirely decouple anode and cathode reactant streams and water management, enabling general analytical methods that separate electrode kinetic from reactant crossover effects. This strategy was exemplified with a direct methanol fuel cell catalyzed with PtRu. No fuel-stream reactant or product crossover other than protons was detected. (C) 2011 Elsevier Ltd. All rights reserved.