Design of an electrochemical cell making syngas (CO+H2) from CO2 and H2O reduction at room temperature

An electrolysis-cell design for simultaneous electrochemical reduction of CO2 and H2O to make syngas (CO + H-2) at room temperature (25 degrees C) was developed, based on a technology very close to that of proton-exchange-membrane fuel cells (PEMFC), i.e., based on the use of gas-diffusion electrodes so as to achieve high current densities. While a configuration involving a proton-exchange membrane (Nafion) as electrolyte was shown to be unfavorable for CO2 reduction, a modified configuration based on the insertion of a pH-buffer layer (aqueous KHCO3) between the silver-based cathode catalyst layer and the Nafion membrane allows for a great enhancement of the cathode selectivity for CO2 reduction to CO [ca. 30 mA/cm(2) at a potential of -1.7 to -1.75 V vs SCE (saturated-calomel reference electrode)]. A CO/H-2 ratio of 1/2, suitable for methanol synthesis, is obtained at a potential of ca. -2 V vs SCE and a total current density of ca. 80 mA/cm(2). An issue that has been identified is the change in product selectivity upon long-term electrolysis. Results obtained with two other cell designs are also presented and compared. (c) 2007 The Electrochemical Society.