Application Of Vertically Oriented TiO₂ Nanosheets Modified Carbon Paper Electrode In MFC

Microbial fuel cell?MFC?is a promising technology,which can convert chemical energy stored in organic matter into electrical energy by the way of extracellular electron transfer?EET?.Anode materials and their surface structure are important factors that affect electricity generation in MFCs.Surface modification by nano-materials is an effective method to optimize performance of an anode.TiO₂ is an excellent material for anode modification due to its very good chemical stability,biocompatibility,abundant sources and environment friendly.However,relatively low conductivity of TiO₂ limits its application in MFC anode.Improving the electrical conductivity of nano-TiO₂ in MFC anode is still a subject to be explored.In this thesis,a designed TiO₂ nanostructure with improved electrical conductivity was fabricated to modify carbon paper?CP?anode of MFC.The effect of the nano-TiO₂ on interfacial electron transfer of electricians was explored and the mechanism was analysized.In addition,nitrogen doping and compositing with conductive polymer were implemented to further increase electrical conductivity of the nano-TiO₂ modified electrode,and high performance anodes for MFC were obtained.The main works and achievements are described as follows:1.An unique vertically oriented TiO₂ nanosheet?TiO₂-NSs?structure was synthesized in situ on the surface of CP electrode by hydrothermal method for the first time.The characterization indicated that rectangular TiO₂-NSs with length of 2 ?M,width of 200-600 nm and thickness of 15 nm had anatase crystal structure.The oriented TiO₂-NSs,which avoided resistance between grain boundaries,provided direct electron transfer pathways and effectively iproved electrical conductivity.In addition,TiO₂-NSs array on electrode surface formed a 3D open channel structure,which not only increased electrode surface area,but also was conducive to interfacial mass transfer.A mixed consortia inoculated MFC using TiO₂-NSs/CP as anode was successfully operated in a long time and stable output was achieved.The maximum output power density was increased by 63%over the MFC using bare CP as anode.The result demonstrated that suitably tailored TiO₂ nanostructures could significantly enhance electricity generation without compositing additional conductive materials,which showed potency of nano-TiO₂ in high performance MFC anode.2.Electron transfer rate constant?ket?of outer membrane c-type cytochromes?OMCs?at TiO₂-NSs/CP electrode was analyzed for the first time using S.loihica PV-4 as model electricigen.TiO₂-NSs being of polar surface groups modified hydrophobic CP into super-hydrophilic TiO₂-NSs/CP.Bio-electrochemical analysis showed that TiO₂-NSs were not only in favor of microbial growth,but also beneficial to regulate redox state of OMCs.The favorable interaction between OMCs and polar groups at TiO₂-NSs surface resulted in more negative mid-point potential Em of OMCs,and thus PV-4 could release electrons more effective at TiO₂-NSs/CP anode.In the meantime,flat-band potential Vfb of TiO₂-NSs moved to more positive potential due to pH decreasing in anolyte.The cooperative shift of redox energy levels concerning electron donor and acceptor was beneficial to interfacial electron transfer kinetics.The ket of OMCs at TiO₂-NSs/CP anode was 3 times faster than that at CP anode.The investigation revealed catalytic effect of nano-TiO₂ on bacterial EET,and further indicated the capability of nano-TiO₂ in fabricating high performance MFC anode.3.Nitrogm dopping via ammonia?NH₃?treatment is an effective method to improve electrical conductivity of nano-TiO₂.TiO₂-NSs/CP electrode was treated in NH₃ atmosphere at different temperatures?400?,500?,600? and 700??,and the performances of PV-4 inoculated MFCs were investigated.The results showed that NH₃ treatment improved maximum output power density of MFCs.The electrode?600-NTiO₂-NSs/CP?treated at 600? exhibited best performance that had the highest conductivity and the lowest charge transfer resistance?Rct?,as well as the largest transient charge storage capacity among all NH₃ treated electrodes.The maximum output power density of PV-4 at 600-NTiO₂-NSs/CP anode was increased 50.3%more than that at TiO₂-NSs/CP anode.4.Composite materials can achieve synergistic effect through complementarity components,which are important for improving electrode performance.The Co-modification of TiO₂-NSs and conductive polyaniline?PANI?were studied.Different amounts of PANI were deposited onto TiO₂-NSs/CP during electrochemical cyclic voltammetry?CV?with 5,10,15,20 and 25 cycles.Bio-electrochemical experiments indicated that TiO₂-20PANI/CP electrode with deposited PANI via 20 cycles of CV had the lowest charge transfer resistance and the largest transient charge storage capacity,which exhibited the best performance.The maximum output power density of PV-4 at TiO₂-20PANI/CP anode?813 mW/m2?was increased 63.6%more than that at TiO₂-NSs/CP anode.Furthermore,PANI was deposited onto 600-NTiO₂-NSs/CP electrode by optimized method,maximum output power density of PV-4 at this anode was 1109 mW/m2,which increased by 123.1%and 36.4%respectively over that at TiO₂-NSs/CP anode and 600-NTiO₂-NSs/CP anode.In summary,vertically oriented TiO₂ nanosheets were successfully fabricated on the surface of carbon paper electrode,and the performance of modified electrode for improving microbial EET and its further optimization were studied in this thesis.The catalytic effect of TiO₂-NSs on interface electron transfer of OMCs was firstly revealed.The results not only give a guideline for designing high performance bio-electrode,but also provide a new perspective for understanding environmental and biological effects of nano-TiO₂.