Yttria stabilized zirconia (YSZ) and calcia stabilized zirconia (CaSZ) electrolyte materials were tested in an intermediate temperature fuel cell using ammonia as a fuel. Silver, platinum and a nickel cermet were used as anode materials in an annular and a pellet design. At 800 degrees C, the nickel cermet achieved ammonia conversions of more than 90%, significantly higher than those obtained with silver and platinum. Direct conversion of ammonia at 800 C, resulted in a power density of 60 mW cm(-2) at a current density of 200 mA cm(-2), for a pellet system with a nickel cermet anode, and a silver cathode and employing an 8 mol% YSZ electrolyte (thickness of 400 N.m). A direct comparison of the performance of a cell running on either hydrogen or ammonia showed that with ammonia the cell generates slightly higher power densities when using a nickel cermet anode. This phenomenon is explained using the Nernst equation, involving the relevant activities at the electrode surface. A comparison of the different oxide ion conducting systems studied under direct ammonia fuel operation shows the high potential of ammonia. (c) 2006 Elsevier B.V. All rights reserved.