Activity and stability of FeTiO(3), MnTiO(3), NiFe(2)O(4), CuFe(2)O(4), NiCr(2)O(4), 2CuO center dot Cr(2)O(3), CuO and Fe(2)O(3) for the atmospheric decomposition of concentrated sulfuric acid in sulfur-based thermochemical water splitting cycles are presented. Catalyst activity was determined at temperatures from 725 to 900 degrees C. Catalytic stability was examined at 850 degrees C for up to 1 week of continuous operation. The results were compared to a 1.0 wt% Pt/TiO(2) catalyst. Surface area by nitrogen physisorption, X-ray diffraction analyses, and temperature programmed desorption and oxidation were used to characterize fresh and spent catalyst samples. Over the temperature range, the catalyst activity of the complex oxides followed the general trend: 2CuO center dot Cr(2)O(3) > CuFe(2)O(4) > NiCr(2)O(4) approximate to NiFe(2)O(4) > MnTiO(3) approximate to FeTiO(3). At temperatures less than 800 degrees C, the 1.0 wt% Pt/TiO(2) catalyst had higher activity than the complex oxides, but at temperatures above 850 degrees C, the 2CuO center dot Cr(2)O(3) and CuFe(2)O(4) samples had the highest activity. Surface area was found to decrease for all of the metal oxides after exposure to reaction conditions. In addition, the two complex metal oxides that contained chromium were not stable in the reaction environment; both leached chromium into the acid stream and decomposed into their individual oxides. The FeTiO(3) sample also produced a discoloration of the reactor due to minor leaching and converted to Fe(2)TiO(5). Fe(2)O(3), MnTiO(3) and NiFe(2)O(4) were relatively stable in the reaction environment. In addition, CuFe(2)O(4) catalyst appeared relatively promising due to its high activity and lack of any leaching issues; however it deactivated in week-long stability experiments. Complex metal oxides may provide an attractive alternative to platinum-based catalyst for the decomposition of sulfuric acid; however, the materials examined in this study all displayed shortcomings including material sintering, phase changes, low activity at moderated temperatures due to sulfate formation, and decomposition to their individual oxides. More effort is needed in this area to discover metal oxide materials that are less expensive, more active and more stable than platinum catalysts. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.