Effect And Mechanism Of Nanomaterial Modified Cathodes On The Performance Of Microbial Electrosynthesis In Acetate Production

Microbial electrosynthesis（Microbial electrosynthesis,MES）employs electroactive microbes as biocatalysts to produce chemicals from CO₂.As a sustainable technology that enables the simultaneous treatment of wastewater and synthesis of chemicals,it has received a lot of attention in recent years.The main factors currently limiting the practical application of MES are low product production rates and difficulties with reactor scale-up.Electrode material optimisation is a key element in the performance of MES.Therefore,this paper investigates the influence of electrode materials on MES from three aspects:carbon nanomaterials,metal nanomaterials and in situ synthesised nanomaterials from electrode biofilms.The main research results of this work are as follows:（1）A MES reactor with powdered activated carbon（PAC）and carbon nanotubes（CNT）as flow electrode materials was constructed to investigate the effect of carbon nanomaterials on the acetate production performance of the flow electrode MES.The results showed that activated carbon was more electronegative compared to carbon nanotubes,but had no significant effect on the final acetate concentration of the MES.Further validation revealed that the mean FHS gene copy number in all experimental groups was 2.0 ± 0.4 × 10⁵mcr A copiesμL^-1.At the same time,the addition of aminated CNT increased biocapacitance and the relative abundance of BRH-c20a.In addition,the addition of 6 g/L of aminated CNT at a constant current of14 m A resulted in a maximum acetate concentration of up to 8.90 g/L.The results of this study are important for exploring the interaction between carbon nanomaterials and microorganisms.（2）The MES system of PAC doped with metal nanomaterials（NPs）for flow electrodes was constructed and evaluated in terms of chemicals production,electrochemical properties and microbial communities.The results showed that Ni and Cu NPs increased the lag period for acetate production.However,Mo NPs had no apparent effect on acetate production,and its presence increased the CH₄ production.However,these metal NPs had a slight influence on the final acetate concentration,Faraday efficiency（FE）,physicochemical properties and electrochemical characterisation.The results of this study will guide the design of advanced electrodes and their further application in microbial electrochemical reactors.（3）Electroactive biofilms were prepared by periodic polarity reversal,and Fe S NPs were synthesized in situ to investigate the effect of different concentrations of Fe S NPs on the bidirectional electron transfer.The results showed that electroactive biofilms with bidirectional electron transfer were successfully enriched in the periodic polarity reversal system.Firstly,the total number of electrons produced during the cathode and anode period was not equal,which might be the result of the"Bio-pseudocapacitance"of the biofilm.CV and DPV tests showed that the experimental groups treated at different concentrations had similar electroactive sites（in the range-200～-380 m V）.Scanning electrochemical microscopy（SECM）analysis further demonstrated that the addition of Fe S NPs increased the reactor current and that the current was positively correlated with the Na₂S₂O₃ to Fe Cl₃ dosing ratio,with a maximum current of 7.7 × 10^-4μA.Firmicutes sp.and Petrimonas sp.were the main functional groups that together facilitate the electron transfer between electrodes and microorganisms.This study provides important reference information for the study of in situ synthesis of nanomaterials for electron transfer in biofilms.In summary,this study addresses the modification of cathodes by nanomaterials:from work on carbon nanomaterials affecting MES product generation,metal nanomaterials affecting MES initiation and microbial enrichment,and in situ synthesis of nanomaterials by electrode biofilms to enhance the electron transfer process.This study has important implications for the construction of highly efficient MES reactors,and is of reference value both in terms of the production of chemicals from CO₂ by electrically driven microorganisms and the elucidation of the electron transfer mechanism.