Design of counter oxidation vs. CO2 electroreduction for efficient formate production on a tin cathode

Aiming to decrease power consumption during CO2 electro-conversion, SO32- oxidation was employed as a counter reaction vs. CO2 electroreduction for formate production on a Tin cathode. The FE and EE for formate at cathodic potential -1.80 vs. SCE/V in 5 h continuous electrolysis were 69.87% and 27.57%, which were increased by ratios of 44.75% and 48.31%, respectively, compared with those in the absence of S032-, together with obvious decrease of the power consumption from 9.04 to 4.81 kWh/kg formate. The electrochemical properties of anolytes show such performance enhancement originated from lower anodic oxidation potential, larger effective area for oxidation and faster oxidation kinetics associated with the conversion of SO32- to SO42-, which reduce the anodic potential and retard side reaction of HER. The effect of SO32-oxidation works on reducing cell voltage and increasing effect current density, which illustrated by morphology changes of cathodes and variations of electrolytes during CO2 reduction. The productive and economical conversion of CO2 to formate at galvanostatic mode verifies the cost-saving effect of SO32- anolyte to the whole cell and provides lab-scale instances for scale-up implementation. This study puts forward another insight for cost-effective CO2 electroreduction, which are of great value in enhancing balance between energy input and output during CO2 utilization, thus having implication in enriching strategy within electroreduction field.