Proton conductivity of Li2SO4-Al2O3 (LA) based electrolyte was determined under non-reducing dynamic conditions using current interruption technique. The performance of LA as electrolyte has been examined at 600 degrees C in a H2S fuel cell with MoS2-NiS as anode catalyst and NiO as cathode catalyst. XRD and XPS results show that Li2SO4 is not stable when heated in pure H2S as it is reduced to Li2S by hydrogen produced in equilibrium amounts from the thermal decomposition of H2S. In contrast, under dynamic operation in a H2S fuel cell the concentration of H-2 is much lower, the reduction reaction does not occur and, surprisingly, Li2SO4 is a chemically stable electrolyte. (c) 2006 Published by Elsevier B.V.