MnO2/reduced graphene oxide nanohybrids as a cathode catalyst for the microbial reduction of CO2 to acetate and isobutyric acid

Abstract

Microbial electrochemical synthesis (MES) can promote an electro-reduction of CO2 to value-added products with nanohybrid catalysts for efficient electron and mass transfer. This study aimed to develop a novel electrode made of nanowires interconnected with flower-like morphology of MnO2 decorated over reduced graphene oxide (rGO) for the conversion of CO2 to volatile fatty acids (VFAs) in a single-chamber MES. The carbon cloth modified with MnO2/rGO nanohybrids could increase CO2 absorption capacity and reduce electron transfer resistance by 70% compared to bare carbon cloth. This modified cathode catalyst enhanced the production of isobutyric acid (15.9 mM) and acetate (3.5 mM), which were 2.09 and 2.91 times higher, respectively, then bare carbon cloth, and the maximum columbic efficiency of 66.4% was obtained for both products. Linear sweep voltammetery of the MnO2/rGO nanohybrids cathode electrode indicated a positive shift of the onset potential under turnover condition. Scanning electron microscopy revealed a diverse enhanced bacterial biofilm growth on the surface of the modified electrode. This study suggests that the MES system with modified cathode using a nanostructured MnO2/rGO nanohybrids catalyst can be used to enhance the CO2 electro reduction to high-value VFAs, which can be further developed as carbon capture and utilization (CCU) technology.