Electrochemical promotion of CO2 hydrogenation on Rh/YSZ electrodes

The electrochemical promotion of the CO2 hydrogenation reaction on porous Rh catalyst-electrodes deposited on Y2O3-stabilized-ZrO2 (or YSZ), an O2- conductor, was investigated under atmospheric total pressure and at temperatures 346-477 degrees C, combined with kinetic measurements in the temperature range 328-391 degrees C. Under these conditions CO2 was transformed to CH4 and CO. The CH4 formation rate increased by up to 2.7 times with increasing Rh catalyst potential (electrophobic behavior) while the CO formation rate was increased by up to 1.7 times with decreasing catalyst potential (electrophilic behavior). The observed rate changes were non-faradaic, exceeding the corresponding pumping rate of oxygen ions by up to approximately 210 and 125 times for the CH4 and CO formation reactions, respectively. The observed electrochemical promotion behavior is attributed to the induced, with increasing catalyst potential, preferential formation on the Rh surface of electron donor hydrogenated carbonylic species leading to formation of CH4 and to the decreasing coverage of more electron acceptor carbonylic species resulting in CO formation.