Mechanism And Application Of Light-driven Holes Interface For Enhancing Current Output On Bioanode In Microbial Fuel Cells

Energy shortage and environmental pollution are the major challenges today.Microbial fuel cells?MFCs?are effective way for generating energy from organic waste through the direct use of electroactive microbes as catalysts driving oxidation reactions on electrodes.However,the practical application of this technology is limited by low current density and shortag of engineering electrodes.Interfacial electron transfer between biofilm and anode is one of the main bottlenecks in determining the current output of MFCs.Therefore,we aim to design photoanode that combines stainless steel felt with photocatalyst,utilizing light to increase potential difference between anode and biofilm,thus enhancing the interfacial electron transfer rate.Main contents and results of this dissertation are as follows:1.The results of XPS and SEM indicated that ?-Fe₂O₃ film was successfully grafted onto the graphite electrode surface and the photocurrent was about 0.78 A m-2.The start-up time of the PMFC with photoanode was shortened to less than half of the MFC.The maximum current density of the PMFC achieved 8.4 A m-2 which was more than double of the BEC?3.9 A m-2?.A rapid decrease and increase in current density were recorded for the OFF and ON of illumination,which mean that the instant photocurrent was one of main reason for the increase of current output.In addition,the results of confocal laser scanning microscopy and bacterial community analysis indicated that illumination could accelerate biofilm formation and enrich exoelectrogens on photoanode.2.To evaluate the effects of different photocatalyst on the current density,CdS and Ti02 were used to modify the photo-exposure side of graphite.The current density of PMFCa.Fe₂O₃ and PMFC TiO₂ was 2.0-fold and 1.7-fold that in MFC?-Fe₂O₃ and MFC-TiO2,respectively.The maximum increase-multiple of current density was achieved in PMFCCds which was 2.8-fold.However,because of the failure of CdS photocatalyst caused by the photocorrosion or oxidation reaction in air environment,the current density of PMFCCdS gradually decreased to 3.8 A m-2,which was similar to MFCCdS· In addition,Photo-electrochemical interaction also could enhance the current output on stainless steel electrode,whose increase-multiple was about 6-fold.Furthermore,we evaluated the effects of photo-generated hole on different anode surface?graphite,carbon-coating,and polyaniline-coating?.The results of current output showed that the stable maximum current density of photo-anode in light was 9.2 and 4.6 A m-2,which was always about 2-fold that in dark without affecting any of those modifications on the microbe-exposure side.Those results showed that the increase-multiple of current density was controlled by photocatalyst and electrode substrate.3.We aimed to systematically evaluate the relative merits of five mainstream modifications on stainless steel electrodes for enhancing current output.A maximum current density of approximately 13.0 A m-2 and 9.0 A m-2 were obtained for the carbon coating and polyaniline coating electrode,respectively?from 3.0 A m-2 of the untreated anode?,which has the largest effective specific surface area.Functionalization with hydrophilic group and electron medium result in the current output rising to 1.5-2 fold,through enhancing bioadhesive and electron transport rate,respectively.Then we reported a high performance composite photo-stainless steel felt anode that combines photocatalyst with 3D structure?stainless steel felt coated with carbon?,utilizing light to further increase the current output in bioelectrochemical systems.The current density of composite photo-stainless steel felt in light achieved?46 A m-2and the volumetric current was 20.9 kA m-3.4.We further introduced a high-performance photo-microbial desalination cell?PMDC?based on photoanode.The maximum current density of the PMDC during operation was 8.8 A m-2 and the salt removal performance in PMDC was always higher than 96%,while that of MDC was lower than 50%.In summary,the photobioanode is a cost-effective,environment-friendly anode with high electrocatalytic activity and long-term stability,which has broad prospects in various processes,including wastewater treatment,bioelectricity generation,bioelectricity synthesis,and hydrogen production.