Steam electrolysis test with a phosphoric acid doped Aquivion (TM) membrane was successfully conducted and current densities up to 775 mA cm(-2) at 1.8 V was reached at 130 degrees C and ambient pressure. A new composite membrane system using a perfluorosulfonic acid membrane (Aquivion (TM)) as matrix and phosphoric acid as proton conducting electrolyte was developed. Traditional perfluorosulfonic acid membranes do not possess sufficient dimensional stability and proton conductivity to be used at elevated temperatures and ambient pressures. The elevated temperature, high potentials and acidic conditions implied that a new and highly corrosion resistant construction material was needed. Tantalum coated stainless steel felt was tested and found suitable as the anode gas diffusion layer. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.