The reduction of CO2/bicarbonate to ethanol driven by Bio-electrochemical system using reduced graphene oxide modified nickel foam

In this study, the reduced graphene oxide modified nickel foam (abbreviated as RGO-Ni) was used as catalytic cathode to reduce CO2/bicarbonate to produce organics in catholyte (containing 0.45 M KHCO3), driven by bioelectrochemical system. The characterization of electrode materials were tested by Scanning Electron Microscope (SEM) and Cyclic Voltammetry curves (CV). The reduction products was analyzed by Gas Chromatograph - Mass Spectrometer (GC-MS). The power generation and the faradic efficiency of the reduction process was determined. The results indicated the RGO-Ni electrode showed much higher catalytic activity than Ni electrode or graphene oxide modified Ni electrode (GO-Ni). The results of GC-MS indicated the reduction products were ethanol (as primary product) and acetone (as by product). Over the RGO-Ni cathode, after 6 h reaction in catholyte with CO2 continuously aerated, the final concentration of Chemical Oxygen Demand (COD) was 389 mg L-1, and the concentration of ethanol was 167 mg L-1. The process maximum power density was 0.52 W m- 2 over RGO-Ni electrode, almost 17 times of the value (0.03 W m-2) using Ni cathode. The faradaic efficiency of the process was calculated as 70%, and the reduction mechanism of CO2/bicarbonate was suggested.

Automated summary

In this study, RGO-Ni was used as a catalytic cathode to reduce CO2 to organics, showing higher catalytic activity and producing ethanol as the primary product. The reduction process on RGO-Ni cathode exhibited significantly increased power density and a 70% faradaic efficiency. The mechanism of CO2 reduction was suggested based on the analysis of reduction products using GC-MS.