Study On The Electroreduction Of Carbon Dioxide Based On The Synergistic Coupling Of Anode And Cathode In Bioelectrochemical System

Electrochemical reduction of carbon dioxide(CO2ER)is an electrochemical technology with promising applications,but the anodic oxygen evolution reaction(OER)in CO2ER system is usually energy-intensive,resulting in a low energy efficiency.Bioelectrochemical system(BES)can convert the chemical energy in wastewater into electricity for recycling,and coupling BES with CO2ER provides the possibility to efficiently drive the high value of CO2 conversion.However,the current density for CO2ER with a superior catalytic performance is usually higher than the generated electric current density by the bioanode in BES.Therefore,direct coupling the bioanodic oxidation reaction and the cathodic CO2ER may result in mismatch of the two half reactions.To solve this key problem,this paper carries out the following work:First,the bioanode in BES and Zn/ZnO alloy plates were employed to form a two-chamber electrolytic cell for constructing BES-CO2ER coupling system.The experimental results showed that the replacement of OER by bioanode has no effect on the catalytic performance of Zn/ZnO alloy plates.Meanwhile,the energy consumption of BES-CO2ER system was reduced by 36%～44%compared with that of OER-CO2ER at current density from 0.5 to 3 mA/cm2.It wass proved that BES-CO2ER coupling system can greatly improve the energy efficiency of the CO2ER system in the current range of 0.5 to 3 mA/cm2.When the operating current was higher than 3 mA/cm2,the output electrons of the bioanode could not match the catalytic current of the Zn/ZnO alloy plates,at that time the OER occurred,resulting in the energy consumption of BES-CO2ER close to that of OER-CO2ER.In order to solve the problem of current mismatch,the Fe(CN)63-/Fe(CN)64"-assisted BES-CO2ER system was constructed,in which Fe(CN)63-/Fe(CN)64--assisted BES-CO2ER system can concentrate the bioelectricity generated by BES to match the high current demand of the CO2ER process.The experimental results show that a high energy efficiency of 135.91%was achieved at a load of 200 Ω and catalytic current of 6 mA/cm2,which is 4.67 times higher than 29.08%of OER-CO2ER.Besides,the overall energy efficiency of whole system remained at a high level during the long-term operationTo couple BES with CO2ER at higher current density,Fe-N-C catalyst was prepared by high temperature calcination method to improve the electric production performance of bioanode,and Fe-N-C/CP electrode was obtained by coating method by modification of catalyst with different loads on the surface of carbon paper(CP).The characterization results showed that the Fe-N-C/CP has good surface roughness,porosity and electrochemical activity,which is conducive to bacterial attachment and interface electron transfer.In the M3C and MFC system,the maximum current and the maximum power density of the of the Fe-N-C/CP with a load of 2 mg/cm2 increased by nearly 2.44 times and 1.26 times compared with the ordinary CP electrode.The surface modification of carbon paper by Fe-N-C enhanced the electric performance of bioanode,which provides the possibility for the operation of BES-CO2ER at higher current density.