The anolyte matters: Towards highly efficient electrochemical CO2 reduction

Abstract

In order to achieve high energy-conversion efficiency during CO2 electro-conversion, OH− oxidation was employed as a counter reaction vs. CO2 electroreduction for formate production on a Tin cathode. The formate faradic efficiency (FE) and production rate were 80.54% and 0.1549 mmol h−1 cm−2 using KOH anolyte at −1.80 V vs. SCE in 8 h operation, which were about 13.71% and 53.03% higher than that for KHSO4 anolyte, respectively. This is mainly due to alkaline anolyte is beneficial to stabilize the catholyte pH, thus avoiding the competitive hydrogen evolution reaction, while maintaining fast electron transfer rate for the formation of CO2*−. Moreover, KOH anolyte achieved the lowest power consumption (4.81 kWh kg−1 formate) compared with KHCO3 and KHSO4. Polarization and electrochemical impedance spectroscopy measurements indicated that such energy-saving performance enhancement originated from low equilibrium potential and fast oxidation kinetics associated with the conversion of OH− to H2O, which reduced the anode potential and cell voltage. This study puts forward another insight for cost-effective CO2 reduction, which is of great value to improve the balance of energy input and output during CO2 conversion, thus having implication in enriching strategy in the field of electroreduction.