The CO2-H-2 reaction was studied at 823-1023 K in a double-chamber proton conducting cell-reactor. The proton conductor was a strontia-zirconia-yttria (SZY) perovskite of the form: SrZr0.90Y0.10O3-alpha The working (cathodic) electrode was a polycrystalline copper film. In the catalytic mode of operation, the reactants were gaseous mixtures of CO2 and H-2 diluted in He and in the electrocatalytic mode, mixtures Of CO2 and He were introduced over the cathode while hydrogen was supplied as H.. The catalytic activity and selectivity of H+ is compared to that of gaseous H-2. (C) 2003 Elsevier B.V. All rights reserved.