Thin proton-conducting electrolyte with composition BaCe0.8Gd0.2O3-delta (BCGO) was prepared over substrates composed of Ce0.8Gd0.2O1.9 (CGO)-Ni by the dry-pressing method. Solid oxide fuel cells (SOFCs) were fabricated with the structure Ni-CGO/BCGO/Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCFO)-CGO. The performance of a single cell was tested at 600 and 650 degrees C, with ammonia directly used as fuel. The open circuit voltages (OCVs) were 1.12 and 1.1 V at 600 and 650 degrees C, respectively. The higher OCV may be due to both the compaction of the BCGO electrolyte (no porosity) and complete decomposition of ammonia. The maximum power density was 147 mW cm(-2) at 600 degrees C. Comparisons of the cell with hydrogen as fuel indicate that ammonia can be treated as a substitute liquid fuel for SOFCs based on a proton-conducting solid electrolyte. (c) 2007 Elsevier B.V. All rights reserved.