Application Of Tungsten-based Nanomaterials In Microbial Fuel Cells

Today,with the increasingly serious problems of environmental pollution and energy shortage,microbial fuel cells(MFCs)have attracted attention of researchers because it can realize sewage treatment and electric energy output at the same time.Since the discovery of microbial electrochemistry in 1911,MFC has made great progress in various aspects in the past hundred years,such as the structure of MFC reactor,the selection of electrogenic microorganisms,the material properties of various components and so on.However,low output power is still the main problem of MFC at present.MFC anode materials are closely related to the performance of MFC.On the one hand,because the anode is the direct contact position of electrogenic microorganisms,the properties of anode materials will directly affect the survival and proliferation of electrogenic microorganisms;on the other hand,when the anode is connected with the external circuit,its electrochemical properties will affect the performance of MFC.Therefore,designing a stable and efficient anode material is one of the key factors to improve the performance of MFC.Based on the excellent performance of tungsten-based nanomaterials in photocatalysis,electrocatalysis and other related fields,as well as the advantages of S,N and other elements in MFCs,different tungsten-based nanomaterials were designed and prepared for MFC anodes,which were suitable for the enrichment of electrogenic microorganisms and achieved good MFC performance.Then,the possible mechanism of the extracellular electron transfer process was investigated.The details are as following:Tungsten oxide(WO₃),sulfur-doped tungsten oxide(S-WO₃)and tungsten nitride nanoparticles(WN)were prepared by hydrothermal method and thermal reduction method,respectively.Tungsten nitride-reduced graphene oxide composites(WN-r GO)were prepared by mechanical composite method.The morphology of synthesized WO₃,S-WO₃and WN nanoparticles was characterized by scanning electron microscopy(SEM)and transmission electron microscopy(TEM).Their physical structures were characterized by X-ray diffraction spectroscopy(XRD),X-ray photoelectron spectroscopy(XPS)and selected area electron diffraction(SAED).The results show that the synthesized S-WO₃and WN nanoparticles have uniform size,high crystallinity and low impurity contents.Furthermore,the electrochemical properties of the anode materials were characterized by cyclic voltammetry(CV)and AC impedance(EIS)tests.Both S-WO₃and WN-r GO anodes show good capacitive and conductive properties,so they can effectively reduce the anode resistance,thus reduce the energy loss of the battery and improve the efficiency of energy recovery.The battery performance of MFCs made of several anode materials was investigated.The results show that compared with the carbon cloth(CC)anode,S-WO₃and WN-r GO as MFC anodes have greatly improved the output voltage and power density of the battery.In terms of output voltage,the peak voltage of S-WO₃anode and WN-r GO anode reaches 577m V and596m V,and the power density is 2005.8m W/m~2and 2976.3m W/m~2respectively,which is higher than that of CC anode by 91.68%and 184.4%respectively.The 16S r DNA sequencing analysis of the microbial community on the anode surface of MFC showed that the electrogenic microorganisms on the anode surface were mainly Geobacter,in which the proportion of Geobacter in the anode biofilm of S-WO₃and WN-r GO reached 77%and 84%respectively,which was higher than that of other control groups in the system.It was consistent with their higher power density,indicating that the relative abundance of electrogenic microorganisms on the anode surface showed a positive correlation with the output performance of the battery.Differential pulse voltammetry and density functional theory were used to analyze the possible mechanism of extracellular electron transfer of WN anode electricity-producing microorganisms,which is dominated by C-type cytochrome in the outer membrane of bacteria.According to the data of the constructed WN and porphyrin iron electron transfer model,WN nanoparticles played a major role in the whole process of electron transfer.This paper provides a reference for the study of tungsten-based nanomaterials in microbial fuel cell anodes.