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+H₂) at room temperature (25C) 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/cm² at a potential of -1.7 to 1.75 V vs SCE (saturated-calomel reference electrode)]. A CO/H₂ 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. 80mA/cm² . 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.