Design of an Electrochemical Cell Making Syngas (CO+H[sub 2]) from CO[sub 2] and H[sub 2]O Reduction at Room Temperature

Abstract

An electrolysis-cell design for simultaneous electrochemical reduction of C O 2 and H 2 O to make syngas ( C O + H 2 ) at room temperature ( 25 ° 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 C O 2 reduction, a modified configuration based on the insertion of a pH-buffer layer (aqueous K H C O 3 ) between the silver-based cathode catalyst layer and the Nafion membrane allows for a great enhancement of the cathode selectivity for C O 2 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 C O ∕ 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.