Study On The Performance Of Microbial Fuel Cell Strengthened By Graphene Modified Electrode

Microbial fuel cell(MFC)is a technology which can directly convert biomass energy into electrical energy without needing energy or power input.So,MFC technology has attracted more and more attention in the field of environment and energy.However,low power density,high cost and low substrate degradation rate,closely associated with electrode performance,limit its practical application.In this study,graphene with high specific surface area and excellent conductivity was selected as modified materials for electrode.Centering on graphene,two-dimensional anode,three-dimensional anode,two-dimensional cathode and cathode microfiltration membrane were prepared,which improved the outputted power density and pollutant removal rate.Firstly,two-dimensional anode modified with graphene was prepared.To make up for the limitations of poor biocompatibility of graphene,proportional polyaniline(PANI)together with graphene was chosen to obtain the PANI dopped graphene by the means of polymerization method in situ,wherein PANI was irregularly attached onto the surface of graphene.The carbon cloth modified with 5% graphene produced the maximum power density(Pmax)of 831 ± 45 mW/m2,which was 1.2,1.3,1.3,1.5,1.8 times of those with 20% graphene,1% graphene,graphene,PANI and carbon cloth,respectively.The polarization resistance according to electrochemical impedance spectroscopy(EIS)analysis was only 24 ± 2 ? in 5% graphene reactors,which was 19.8% of that of the carbon cloth.Exoelectrogen take full advantage of the merits of graphene and PANI.Graphene with excellent conductivity improved the efficiency of electron transfer,and PANI was conducive to biomass density,which reduced polarization resistance and enhanced the bioelectrochemical performance.During the preparation of PANI doped graphene above-mentioned,the binder was needed,which degraded electrode conductivity and electron transfer efficiency.For the purpose of simplifying process of modification,the secondary bond forces were exploited to in situ modify the carbon cloth with PANI and graphene without binder.The secondary bond forces include ?-? stacking,hydrogen bonds and electrostatic forces between the carbon cloth,graphene and PANI.The MFC reactors with PANI/graphene modified carbon cloth(PANI+G+CC)anode achieved the highest voltage with 573 ± 37 mV,and produced the Pmax of 884 ± 96 mW/m2,which was 1.3 and 1.9 times of those with the carbon cloth control.Based on CV scanning and attenuated total reflectance-Fourier transform infrared spectroscopy(ATR-FTIR)spectra,it was speculated that the weakly acidic microenvironment derived from bio-anode delayed or impeded the deprotonation of PANI and made PANI hold a certain level of conductivity for electron transfer.The three-dimensional graphene anode(3D-G)was prepared by self-assembly method under optimum graphene concentration and reaction temperature.The as-received 3D-G electrode featured inflexibility,crumpled surface,macroporous structure(with dozens of microns in pore space),high specific surface area(188 m2/g),good conductivity and low cost,favoring the high bacterial loading capacity and enhancing the extracellular electron transfer(EET)efficiency.Equipped with the prepared 3D-G anode in air-cathode single chamber MFC reactor,the Pmax increased to1516 ± 87 mW/m2 in the 3D-G reactor from 877 ± 57 mW/m2 in the graphite felt control and from 584 ± 39 mW/m2 in the carbon cloth control after 2 weeks of operation.Moreover,the Pmax of reactor with 3D-G anode decreased only by 15% after 2 months of operation,which showed durability of the anode due to not easily blocked macropore.Normalized to the cost of anode,the Pmax in the 3D-G reactor was 93 and 133 times of those in graphite felt and carbon cloth reactors,respectively.Dynamic analysis results(CV,Tafel and EIS)showed that the 3D-G anode improved the efficiency of EET due to appropriate structure and good conductivity.In order to enhance the cathode performance and reduce the costs,optimum graphene was mixed with activated carbon,improving hydrophobicity and conductivity of cathode.The results of CV showed that the scanning current was largest in 10% graphene(mass ratio).The results of LSV demonstrated that the scanning current of 10% graphene was only slightly smaller than Pt cathode.According to Tafel analysis,the exchange current density of was 0.22 ± 0.03 mA/cm2,higher than 0.20 ± 0.02 mA/cm2 of the Pt cathode.The electron transfer number of 10% graphene during oxygen reduction reaction was 3.2 ± 0.3,higher than 2.8 ± 0.3 of the Pt cathode.After all the reactors started successfully,the Pmax of 10% graphene reached to 1406 ± 88 mW/m2,a little lower than 1457 ± 92 mW/m2 in Pt reactors.Due to short discharging time,both COD removal and CE efficiencies in Pt reactors were lower than that in 10% graphene reactors.The results of EIS demonstrated that the polarization resistance was only 17 ± 2 ? in 10% graphene reactors,lower than 20 ± 2 ? in Pt reactors.No matter from the aspects of catalytic efficiency or cost of electrodes,10% graphene rivaled Pt.Graphene modified cathode microfiltration membrane(G-FM)was prepared with reduced graphene oxide(RGO)on stainless steel mesh base by the method of immersion-precipitation phase transformation.The pure water flux and mean pore size of the prepared G-FM was 712 ± 62 L/(m2·h·bar)and 0.09 ± 0.01?m.Equipped with the prepared G-FM,the coupled configurations of MBR with MFC removed 96.6 ± 3.9% COD,95.8 ± 5.7% NH3-N and 94.7 ± 5.2% total nitrogen and generated 349 ± 19 mW/m2 bioelectricity from the synthetic municipal wastewater.Moreover,the membrane fouling was reduced due to enhanced hydrophilicity and electrostatic repulsive forces.Applied graphene in MFC electrode modification,the running cost of MFC would reduce,and the performances of electricity generation or substrate removal efficiency would increase,which can powerfully promote the practical and large-scale application of MFC.