Efficient solar-to-acetate conversion from CO2 through microbial electrosynthesis coupled with stable photoanode

Abstract

Integration of microbial electrosynthesis (MES) with renewable energy supply has been proposed as a novel approach for energy storage and CO2 transformation into fuels and chemicals. However, the efficiency of renewable energy conversion into biochemicals is yet to be improved in MES. In this study, molybdenum-doped bismuth vanadate was deposited on fluorine-doped tin oxide glass (FTO/BiVO4/Mo) to serve as MES photoanode for efficient solar energy harvesting and reduction of overpotential for oxygen evolution reaction (OER). By applying a fixed bias of 3 V to MES systems under 0.5 sun illumination, a more negative cathode potential (–0.72 ± 0.03 V vs. SHE versus –0.38 ± 0.03 V vs. SHE in the dark) was achieved owing to the reduced OER overpotential at FTO/BiVO4/Mo photoanode, which led to a 25% increase in current density and 46-fold increase in acetate production rate. Higher electron recovery (~62%) and excellent stability (7 days) were also observed in MES reactors with sun illumination on FTO/BiVO4/Mo photoanode. Based on acetate production and energy input from simulated sunlight, 0.97 ± 0.19% solar energy was theoretically converted into acetate, which is one of the highest conversion efficiencies ever reported in hybrid MES systems. These results demonstrate that integrating FTO/BiVO4/Mo photoanode with MES systems could significantly enhance the solar-to-biochemical conversion efficiency by lowering the energy requirement for initiating the anodic OER and maintaining the negative cathode potential, which enables MES technology to be economically more viable for renewable energy storage and CO2 valorization.