Study On Photocatalytic Fuel Cell Coupling Photoelectric Strengthening Using Three-dimensional TiO₂ Photoanode Formed On Ti Mesh

With the emergency of energy crisis and environmental pollution,developing clean and renewable energy is increasingly gaining popularity for researchers in the field of environmental energy.As a promising technology,photocatalytic fuel cells?PFCs?offer several advantages in terms of simultaneous refractory wastewater treatment and electricity generation,which poses huge potential in wastewater treatment process.PFCs have been intensively researched in the field of electrode material development,reactor configuration design and working mechanism.However,PFCs is still limited in many aspects towards practical application.Firstly,photocatalyst is attractive due to its unselective oxidation for almost all refractory compounds.However,a high degree of recombination between the photogenerated electrons and holes in TiO₂ still presents challenge for wider its application.Besides,the research of cathode systems is limited,and cathodic oxygen reduction of the PFCs remain a major challenge in terms of stable operation,affinity to environment,and suitable for application.This study was carried out on reducing the adverse effects of combination of electron-hole pairs for enhancement of organic wastewater treatment in photoanode.Meanwhile,coupling cathode showed good environmental affinity for photoanode to realize the stable operation of the PFC.Electrochemical anodization was performed with Ti mesh for the preparation of TiO₂ nanotubes array with well-radial-3D structure,which grown vertically on the Ti wire.The nanotubes had an average diameter of 500 nm and length of 5?m.The XRD patterns demonstrated the typical crystal phase of TiO₂ was anatase.The photoelectric properties of the TiO₂ electrode were demonstrated by LSV.A maximal current of 3.1 mA was achieved upon introduction of UV irradiation,while,the photocurrent disappeared without the UV irradiation.The TiO₂/Ti photoanode also showed an instant photoresponse with or without illumination.The photoelectrode could obtained 90%targeted pollutant removal after several use,indicating its stable operation property.SEM result showed little change of surface morphology of TiO₂ nanotube,which was the main reason for its stable operation.These results demonstrated the prepared photoelectrode could well meet the performance requirement of stable operation and high efficiency for PFCs.A three-chamber photocatalytic fuel cell?PFC?was constructed based on in-situ utilization of junction potential created by salt concentration gradient between the chanbers for increasing the separation efficiency of photogenerated electrons and holes.The photocatalytic performance could be enhanced with the reduced combination efficiency of electron-hole pairs,facilitating the current output performance.The average voltage output increased rapidly from 170.00 to 319.70 m W/m² with the increase in Na Cl concentration from 5 to 45 g/L,and the correspnding values for power densities increased from 170.0 to 319.7 m W/m².The cathode potentials were nearly stable and barely affected by the change of Na Cl concentration,indicating the change of voltage was mainly due to the change of anode potentials.Meanwhile,the kinetics constants for Rh B increased from 0.0333 to 0.0505min^-1with the increase in Na Cl concentration.Compared with the control two-chamber reactor,the three-chamber PFC took the advantages in electricity generation performance and pollutant degradation rate.These results show that integrating salinity gradient power into PFC system is an effective method to enhance the overall performance of PFC.A PFC based on in-situ utilization of generated electricity using a capacitor-based circuit was developed.The system was operated in alternate charging and discharging?ACD?mode for enhancing the current output and strengthening pollutant removal efficiency.With the decrease of switch time?T_s?from 10 min to 1 min,the current densities increased from 1.86±0.02 to 2.58±0.08 A/m²,and the Rh B degradation rate increased from 0.03879 to 0.05931 min^-1.These current densities were higher than that obtained in continuous energy harvesting mode using resistor?0.80±0.02 A/m²?,and the Rh B degradation rate was also higher than that of 0.0281 min^-1,suggesting the enhancement effect of ACD mode on pollutant degradation.The preparation of Ag/TiO₂ was carried out by photodeposition.SEM-EDX image of Ag/TiO₂ showed that Ag particles were uniformly distributed on the surface and wall of TiO₂ nanotubes.The average Ag weight percentage reached27.59%.High-resolution TEM?HRTEM?clearly showed the well-defined lattice fringes of the Ag particles with an average size of 20 nm.The UV–vis absorption spectra and PL spectra showed extended light absorption properties in visible light region and reduced recombination of the photogenerated carriers and of TiO₂A novel biocathode-drived PFC?bio-PFC?with an Ag-doped TiO₂ photoanode and microbial-catalyzed biocathode was constructed.The biocathode took advantages in stable operation and affinity to environment.The Rh B degradation rate was 0.0451 min^-1,which was higher than that of undoped one(0.0301 min^-1).The stable voltage output was 396.47±3.99 mV using Ag/TiO₂ photoanode,which was higher than that of undoped one?306.32±11.1 m V?.A maximum power density of 318.19 m W/m² was obtained which was 57.09%higher than that of undoped one.Pyrosequencing revealed that the cathodic microbial community was dominated by electrographic microorganisms including Acinetobacter sp.,Shewanella sp.,and nitrifiers?Nitrospira sp.,Nitrobacter sp.,Nitrosococcus sp.?,which ensured the oxygen reduction in biocathode.