Catalytic Performance Optimization And Function Regulation Of Microbial Fuel Cell Cathodes Based On Multi-functional Integration

Microbial fuel cell?MFC?is a new technology that produces electricity from pollutant removal process.It has the advantages of mild operating conditions,high resource utilization,pollution-free,etc.However,MFC has a certain selectivity for substrates,and its power generation needs to be further improved.The high cost of cathode and the decline of cathode performance after scaling up limit its engineering applications.At present,the regulation of cathode electrochemical performance and coupling with functions other than oxygen reduction are the key strategies to improve cathode efficiency,organic matter degradation and power generation.In this dissertation,the wastewater treatment and electricity generation performance of MFCs were enhanced by the design of novel catalysts,the coupling of MFC with electro-Fenton?EF?,and the mechanism of the influence of MFC cathode properties on power overshoot was also studied.?1?Fe and N co-doped carbon–based MFC cathode catalyst?Fe/N/C?was prepared.The catalytic performance of oxygen reduction was improved by Fe and N doping,and the electrode stability was improved by adjusting the textural properties of the catalyst.Fe/N/C catalyst was prepared by high temperature pyrolyzing of biomass capsuling polymer synthesized through polycondensation between melamine resin pre-polymer and ammonium ferric citrate.The Fe source ratio and pyrolysis temperature had great influence on textural property and element state of the final catalyst.The prepared Fe/N/C catalyst exhibited excellent ORR catalytic performance and stability in neutral solution due to favorable nitrogen doping,carbon skeleton embedded Fe₃C nanoparticles and reasonable pore structure.Single-chamber air cathode MFC test showed the Fe/N/C cathode could produce a maximum power density?MPD?of 1166 mW m^-2,which was 1.4-fold higher than the AC&CB cathode.The MPD for Fe/N/C cathode only decreased by 7%after60-day operation.Density functional theory study was conducted to explore the mechanism of oxygen reduction on N-doped carbon based catalyst.The mechanisms of oxygen reduction on graphitic N-doped and pyridinic N-doped catalysts were theoretically analyzed.The hexagonal ring graphene model was adopted to research adsorption and reduction path of molecular oxygen on N-doped graphene.Theoretical calculation reveals that the graphitic N dopant was superior to pyridinic N in terms of ORR performance improvement.The electricity generation variance of MFCs with different nitrogen-doped Fe/N/Cs can be explained by theoretical calculation results.?2?The Fe/N/Cs were adopted as cathode catalysts and the relationship between cathode capacitance and MFC power overshoot was studied based on MFC pulse discharge characteristics.It was found that MFC with relatively low capacitance cathode exhibited power overshoot in polarization test.Therefore,the relationship between cathode capacitance and D-type power overshoot was studied.Here,the mechanism of power overshoot was investigated with single-chamber MFCs assembled with low-capacitance carbon cloth anode and Fe/N/C cathodes of distinct capacitances.It was revealed that insufficient electricity generation of anode was responsible for power overshoot generation,and the cathode capacitance can enhance MFC capacitance,thus compensating for the shortage of power generation and anode capacitance.Power overshoot could be eliminated with higher capacitive cathode?7.79 F?compared to the one with lower capacitive cathode?3.74 F?when assembling MFC with low capacitance anode?0.032F?.Shortening external resistance connection time of polarization curve test can also relieve or avoid power overshoot.The enlightenment is that when assembling MFC,simultaneously low capacitance of anode and cathode should be avoided in order to prevent power overshoot from negatively affecting the evaluation of power generation performance.?3?The nZVI@MAC dual function air cathode was synthesized and the single-chamber bio-electro-Fenton?BEF?system was constructed to enhance the degradation of complex organic matters in MFC.The power generation,pollutant treatment efficiency and energy recovery of MFC were improved.Activated carbon?AC?,modified by co-pyrolyzing AC with glucose,was used as MFC cathode catalyst.The modified AC?MAC?exhibited higher oxygen reduction catalysis in neutral solution and produced more H₂O₂ than AC in MFC.Then a dual-functional cathode was fabricated by doping nano-zero-valent iron onto MAC?denoted as nZVI@MAC?.Single-chamber BEF system was assembled with nZVI@MAC cathode and adopted to treat real landfill leachate.It was revealed that COD removal and columbic efficiency for single-chamber BEF were higher than that of AC cathode MFC.The higher COD removal?79%vs 68%?of cycle operation can be ascribed to synergistic effect of cathodic Fenton oxidation and anodic microbial oxidation,which improved degradation of recalcitrant organic matters.The higher columbic efficiency?30%vs 5%?can be attributed to the EF-induced inhibition of anaerobic fermentation,which competes substrate with anodic exoelectrogens.The energy recover efficiency was also greatly enhanced by this inhibition.The strong oxidative hydroxyl radicals produced by the cathode also had the function of anti-biofouling,which can be conducive to the long-term stability of the cathode.?4?A two-chamber MFC and an air-cathode EF were coupled to enhance MFC power generation and system efficiency of EF by using Fe³⁺produced in EF as electron acceptor in MFC cathode.The air-cathode EF was coupled with MFC carbon felt cathode to construct dual-cathode EF system,aiming to accelerate Fe³⁺reduction in air-catode EF and improve power generation in MFC.Synergistic improvements of MFC power generation and electro-Fenton reaction were achieved through regeneration of Fe²⁺on MFC cathode.Gas diffusion electrode?GDE?was fabricated by adopting activated carbon/graphite powder mixture.The as-prepared activated carbon&graphite?AC&G?GDE showed high H₂O₂ production but very slow rate for Fe³⁺reduction.The reduction kinetics constant for Fe³⁺on AC&G GDE electrode(8.7×10^?3 min^?1,-0.4 V vs.Ag/AgCl)was much slower than carbon felt cathode(6.4×10^?2 min^?1,-0.2 V vs.Ag/AgCl).Then a carbon felt cathode MFC was coupled with GDE electro-Fenton system to accelerate Fe²⁺regeneration in EF.The coupled dual-cathode EF system was utilized to degrade Rhodamine B.The Rhodamine B removal rate constant and mineralization current efficiency were 64%and 42%higher than that of un-coupled electro-Fenton system,respectively.On the other hand,the MFC power generation was greatly enhanced by coupling with electro-Fenton due to higher Fe³⁺/Fe²⁺redox potential than oxygen reduction.Its MPD can be as high as 1.51 W m^?2,much higher than that of un-coupled MFC(0.26 W m^?2).