The reaction Of C3H8 decomposition was studied in a proton conducting cell-reactor in the presence of H2O vapor in the feed gas. The proton conductor was a strontia-ceria-ytterbia perovskite disk of the form: SrCe0.95Yb0.05O3-alpha. Reaction temperature varied between 873 and 1023 K and a polycrystalline palladium film was used as the working electrode-catalyst. The H-2 produced by the reaction was electrochemically transported through the walls of the proton conducting disk to the outer reactor-chamber. Upon increasing the H2O partial pressure from 0.3 to 2.8 kPa, a 4-fold increase on the reaction rate was observed. Upon proton "pumping" to the outer chamber, an up to 90% of the produced hydrogen was electrochemically separated from the reaction mixture. (c) 2005 Elsevier B.V. All rights reserved.