Fabrication Of Metal Chalcogenides/Graphene Composite Materials And Its Performance As Microbial Anode

Microbial fuel cells（MFCs）can turn organic into electricity and is getting more and more attention.Fabrication of high performance anode material is one of the key factors that hinder its development.Properities of anode materials affect microbial adhesion,electron transfer,metabolism and microbial community structure.Tradational anode material has a relative low surface area,low biocompatibility and high electron transfer resistance.To solve these problems,transition metal chalcogenides and graphene were combine to fabricate MFCs anodes(Fe S₂/r GO,Co S₂/r GO and Fe_xCo_1-x/r GO anode).Utilizing the advantages of graphene’s good conductivity,large surface area,and iron-cobalt sulfide that can promote electron transfer and quickly accumulate electricity-producing bacteria,it’s expected that they can improve the biocompatibility and electrochemical performance of the anode.Also,the microbial community in the anode chamber was analyzed.Firstly,Fe S₂/r GO composite was synthesized by hydrothermal reaction.They were prepared into two-dimensional anodes and three-dimensional independent anodes respectively.During operation,it was found that the two-dimensional anode had a smaller charge transfer resistance and was more stable.Comparing Fe S₂/r GO anode,r GO anode and CC anode,it is found that Fe S₂/r GO anode shorten the startup period to 54 h（shorten by 90.2%compared to CC anode）,obtain a higher plateau voltage,higher power density（3.22 W/m²）,greater COD removal rate（86.4%）and higher coulombic efficiency（9.34%）.Electrochemical tests show that Fe S₂ can act as a“anchor”to mediate direct electron transfer involving cytochrome proteins.Fe S₂/r GO anode has good biocompatibility which can accumulate more exoelectrogen Geobacter（79%）in the mix-culture anode bifilm community.Fe S₂ and Co S₂ have similar properties,but Co S₂ has better conductivity.In order to further improve the electrochemical performance of the anode,Co S₂/r GO composite was synthesized.By optimizing the synthesis conditions,the optimal synthesis conditions were obtained by hydrothermal reaction at a 1:1 mass ratio of sulfur source and graphene oxide and then conduct a heat treatment,which gain Co S₂/r GO composite with uniformly distributed particles and the best electrochemical performance.Assembling it as anodes into MFCs,the cell started quickly in 57 h,and obtained a maximum power density of 3.43 W/m²,a COD removal rate of 92.2%,and a coulombic efficiency of 13.7%,and relatively improve6.5%,6.7%and 46.7%compared with Fe S₂/r GO anodes.Analyzing the anode biofilm microbial community,it is found that the abundance of the exoelectrogens Geobacter in the Co S₂/r GO（S/r-1）anode is the highest,which is 72.09%.There is a certain correlation between the content of graphene and the exoelectrogens Pseudomonas in the anode biofilmFe S₂/r GO and Co S₂/r GO have their own advantages in start-up time,resistance and power density of growing biofilms.Therefore,the synthesis of iron cobalt sulfide Fe_xCo_1-x/r GO complex is expected to combine the advantages of Fe S₂/r GO and Co S₂/r GO to further improve the anode performance.Assembled into MFCs,it took67 h until MFCs start up,and gain the highest plateau voltage of 0.646 V,COD removal rate of 90.5%,Coulomb efficiency of 10.78%and the maximum power density of 3.65 W/m² and it improved 6.4%compared to Co S₂/r GO.After long-term operation,it can still maintain a high voltage.CV and DPV results show that the mechanism of accelerating electron transfer may mainly derived from the promotion of direct electron transfer mediated by outer membrane proteins.High-throughput sequencing results show that there are four exoelectrogens bacteria Geobacter,Acrobacter,Comamonas and Pseudomonas in the anode biofilm microbial community.The abundance Acrobacter in Fe_xCo_1-x/r GO anode biofilm is much larger than that in CC anode biofilm.Similarly,the abundance of Pseudomonas and the presence of graphene(Fe_xCo_1-x/r GO anode and r GO anode)show a certain correlation.From view of bacterial space distribution,the community structure of the microorganisms in the anolyte of different anode materials and the biofilm attached to the anode surface were investigated,and they were found to be quite different,but there were some common rules:the abundance of Geobacter in the solution was much lower than in biofilm.Meanwhile,different species of Pseudomonas and Comamonas were enriched in the solution and on the anode surface respectively.P.otitidis was enriched in the anolyte,and P.guangdongensis,P.citronellolis and C.denitrificans were mainly concentrated in the biofilm attached to the anode.The principal component analysis shows that community structure is strongly affected by the growth or attachment environment.In summary,these three synthesized transition metal sulfide/graphene composites all show good performance as MFCs anodes.Among them,Fe_xCo_1-xS₂/r GO anode showed the highest power density（3.65 W/m²）;Co S₂/r GO anode achieved higher COD removal rate（92.2%）and coulombic efficiency（13.7%）;Analyzing the anode biofilm communities of different anode materials,it was found that,Fe S₂/r GO enriched more Geobacter,Co S₂/r GO and Fe_xCo_1-x/r GO enriched more species of exoelectrogens.Anode materials affect the performance of MFCs and anode microbial community in many aspects,which are of great help for the future design of high-performance MFCs anode materials.