Bulk pH contribution to CO/HCOO− production from CO2 on oxygen-evacuated Cu2O electrocatalyst

Abstract

Controlling product selectivity is regarded as one of the main barriers in the application of Cu-based electrodes to electrochemical CO2 reduction and hence significant studies on experimental factors to improve the selectivity towards desired products. In particular, two pH parameters appear to be important in controlling product selectivity of the CO2 reduction process. We study how both bulk and local pH conditions affect product distributions during CO2 reduction on oxygen-evacuated Cu2O electrode. In contrast with previous studies of local pH effect on CO2 reduction using metallic Cu, our results suggest that not always is the preferential production of C2 compounds (C2H4+C2H6) achieved by high local pH condition irrespective of catalyst materials, but rather bulk pH condition could contribute to ability to control product selectivity. It is finally demonstrated that the bulk pH effect, often underestimated but related to carbonate speciation, is associated with the direct reduction of HCO3 − to HCOO−. © 2016 Elsevier B.V.