Anion dependent CO/H2 production ratio from CO2 reduction on Au electro-catalyst

•The anion effect of 4 electrolytes for CO2RR on Au catalyst are investigated.•The specific adsorption of anions could contribute to suppressing HER.•Chloride anion plays a notable role as increasing CO/H2 production ratio.•Phosphate anion contributes to decrease CO/H2 production ratio.

In this study, we first demonstrate that CO production selectivity from CO2 on Au electro-catalyst depends on the type of electrolyte anion. Comparing the faradaic efficiencies of H2, HCOO− and CO in the presence of different anions such as Cl−, HPO42−, SO42− and HCO3− at constant potential of −0.7 V (vs. RHE), we observe that the CO/H2 ratio could be enhanced due to strongly adsorbed anion such as Cl−. Although HPO42− is more strongly adsorbed than SO42− and HCO3− on the surface of electrode, CO2 reduction in HPO42− containing solution exhibited a minimum faradaic efficiency of CO (11%) but a maximum faradaic efficiency of H2 (70%). Based on physicochemical analytical tools (LSV, EIS, SEM, XPS and XRD) and according to previous studies, we conclude that the product distribution is associated with distinct properties caused by characteristic of each anion when adsorbed on the electrode surface such as specific adsorption strength and intrinsic characteristic of anions.

Graphical abstractDepending on electrolytes containing different anions, CO/H2 production ratio of CO2 electroreduction on Au catalyst was differently observed. Usually, a specific adsorption strength of anions played a key role in determination of CO/H2 ratio by a suppressing hydrogen evolution reaction. However, unlike that, certain anions such as chloride and phosphate differently contribute to increase CO/H2 ratio due to their intrinsic characteristics.Download high-res image (97KB)Download full-size image