Proton-conducting solid electrolytes composed of gadolinium-doped barium cerate (BCG) or gadolinium and praseodymium-doped barium cerate (BCGP) were tested in an intermediate-temperature fuel cell in which hydrogen or ammonia was directly fed. At 700 degrees C, BCG electrolytes with porous platinum electrodes showed essentially no loss in performance in pure hydrogen. Under direct ammonia at 700 degrees C, power densities were only slightly lower compared to pure hydrogen feed, yielding an optimal value of 25 mW cm(-2) at a current density of 50 mA cm(-2). This marginal difference can be attributed to a lower partial pressure of hydrogen caused by the production of nitrogen when ammonia is decomposed at the anode. A comparative test using BCGP electrolyte showed that the doubly doped barium cerate electrolyte performed better than BCG electrolyte. Overall fuel cell performance characteristics were enhanced by approximately 40% under either hydrogen or ammonia fuels using BCGP electrolyte. At 700 degrees C using direct ammonia feed, power density reached 35 mW cm(-2) at a current density of approximately 75 mA cm(-2). Minimal loss of performance was noted over approximately 100 h on-stream in alternating hydrogen/ammonia fuels. Crown Copyright (c) 2005 Published by Elsevier B.V. All rights reserved.