Performance Study Of 2D G-C₃N₄ Or MoS₂ Modified Composite Photoanode Based Photocatalytic Fuel Cell

Photocatalytic fuel cell（PFC）is a new advanced oxidation technology that can generate electricity while degrading pollutants.The most direct and effective way to develop efficient PFC system is to enhance the photoelectrochemical properties of photoanode.In this paper,BiOBr with respond to visible light and TiO₂with strong chemical stability,are selected as the substrate materials.However,they have some disadvantages,such as fast recombination rate of photogenerated carriers and weak electrochemical performance.In the new two-dimensional materials,two-dimensional g-C₃N₄with graphene like structure and two-dimensional Mo S₂with layered structure have visible light absorption characteristics and excellent electrochemical properties.Three kinds of composite photoanodes（g-C₃N₄/BiOBr,g-C₃N₄/TiO₂and Mo S₂/TiO₂）were prepared by two-dimensional material modification to overcome the defects of substrate materials.The composite photoanode is used in the PFC system to explore the electricity generation performance of PFC.The research contents and main results of this paper are as follows:（1）Nano g-C₃N₄/BiOBr composite photoanode was prepared by modifying BiOBr with g-C₃N₄with graphene like structure.The characterization results of FTIR and XRD show that two-dimensional g-C₃N₄and tetragonal phase BiOBr are stable.The calculation of solid UV Vis DRS transmittance and valence band conduction band shows that there is a type II heterostructure between g-C₃N₄and BiOBr in the composite photoanode.After g-C₃N₄composite,the photocatalytic performance of the composite photoanode was significantly enhanced.In the linear sweep voltammetry（LSV）diagram,the photocurrent density of the composite photoanode（CNBOB-2）is18 times higher than that of the pure BiOBr,up to 1.3 m A/cm²,the carrier migration resistance in the electrochemical impedance（EIS）spectrum decreased from 2132Ωto610Ω;negative shift of flat band potential in Mott-Schottky（M-S）spectrum.CNBOB-PtPFC was composed of CNBOB-2 and Pt.to explore the power generation performance.When the reaction substrate is Rhodamine B with a concentration of 50ppm and pH 11,PFC has the best power generation capacity.The values of short-circuit current(J_sc),open circuit voltage(V_oc)and power density(P_max)are 0.066m A/cm²,0.80 V and 0.014 m W/cm²respectively.（2）Aiming at the defects of TiO₂,two-dimensional g-C₃N₄with visible light response and graphene like structure was modified to obtain g-C₃N₄/TiO₂composite photoanode.The FTIR and XRD characterization showed that two-dimensional g-C₃N₄and anatase TiO₂existed stably in the composite photoanode.In the UV Vis DRS absorbance test,it is found that the absorption capacity of the composite photoanode to visible light is enhanced,and the maximum absorption wavelength is428 nm,which is higher than that of TiO₂（418 nm）.According to the calculation of valence band and conduction band,type II heterojunction is formed between g-C₃N₄and TiO₂.After two-dimensional g-C₃N₄modification,g-C₃N₄/TiO₂composite photoanode showed good photoelectrochemical properties in photoelectrochemical tests（LSV,EIS,M-S）.The highest photocurrent density（CNT-2）increased to 1.3m A/cm²,the migration resistance decreased from 11031Ωto 509Ω,and the flat band potential moved from 0.3 negative to-0.4 e V.CNT-PtPFC was formed with CNT-2and Ptelectrode.The reaction substrates of different kinds of pollutants,gradient concentration and gradient pH were explored.It was found that phenol with concentration of 10 ppm and pH of 7 had the highest power generation capacity,and J_sc,V_ocand P_maxwere 0.27 m A/cm²,0.70 V and 0.081 m W/cm²respectively.（3）In order to overcome the defect that TiO₂can not absorb visible light,wide band gap and fast recombination rate of photo generated carriers.A nano Mo S₂/TiO₂photoanode was designed and fabricated.And a new photocatalytic fuel cell（PFC）consisting of Mo S₂/TiO₂photoanode and Mo S₂/Ni foam cathode was prepared.After loading two-dimensional Mo S₂on the surface of TiO₂,the characterization shows that the Mo S₂/TiO₂photoanode has type II heterostructure.The photoelectrochemical properties were significantly enhanced,which was manifested in the broadening of light absorption range,the reduction of band gap,the increase of photocurrent density and the decrease of migration resistance.The maximum absorption wavelength of Mo S₂/TiO₂composite photoanode increased from 420 to 430 nm;the photocurrent density increased from 1.25 to 3.45 m A/cm²;the migration resistance is reduced from10603 to 5188Ω.It is proved that the modification of Mo S₂accelerates the migration rate of photogenerated electron hole pairs and enhances the separation efficiency.Through the PFC performance test,it was found that the MT-MN PFC had the highest open-circuit voltage（0.7 V）,short-circuit current（1.04 m A/cm²）and actual maximum power density（0.114 m W/cm²）with 20 ppm phenol as the reaction substrate.The electrical performance is significantly higher than other reported PFC with TiO₂as photoanode or substrate.At the same time,the prepared PFC system has good organic wastewater treatment capacity.After 4h illumination,the removal rate of RhB reached 69.16%.During the degradation of RhB by PFC,holes,hydroxyl radicals,superoxide radicals and hydrogen peroxide were generated to remove RhB.