The kinetics and the electrochemical promotion of the hydrogenation of CO2 on polycrystalline Ru deposited on BZy (BaZr0.85Y0.15O3-alpha + 1 wt% NiO), a proton conductor in wet atmospheres, with alpha approximate to 0.075, was investigated at temperatures 300-450 degrees C and atmospheric pressure. Methane and CO were the only detectable products and the selectivity to CH4 could be reversibly controlled between 15% and 65% by varying the catalyst potential by less than 1.2 V. The rate and the selectivity to CH4 are very significantly enhanced by proton removal from the catalyst via electrochemically controlled spillover of atomic H from the catalyst surface to the proton-conducting support. The effect is strongly non-Faradaic and the apparent Faradaic efficiency of methanation takes values up to 500 and depends strongly on the porous Ru catalyst film thickness. The observed strong promotional effect, in conjunction with the observed reaction kinetics, is in good agreement with the rules of electrochemical and chemical promotion. (C) 2015 Elsevier Inc. All rights reserved.