The Study Of High-Power-Output Microbial Fuel Cell Based On Nitrogen/Sulfur/Iron Co-Doped Carbon Catalyst

Microbial fuel cell（MFC）is a new technology which combines pollutant removal and production capacity.Because it has high reduction potential,oxygen in the air is often used as the cathode electron acceptor of MFC（air micirobial fuel cell,ACMFC）.However,the oxygen reduction reaction at ACMFC cathode is difficult to occur without cathode catalyst,and the capacity of ACMFC is also low.Pt/C has been considered to be an effective electrocatalyst now.But it suffers from high cost so that the cost of MFC is greatly high.Now the study of MFC is still in the small-scale laboratory level.Therefore considerable efforts have been devoted to developing low cost and high efficient catalyst.Besides,O₂ is usually used as MFC cathode electron acceptor in previous studies.Howere,the research of other gas that are used as cathode electron acceptors is very scarce.As is known to all,NO is major pollutant of flue gas.So if NO can be used for MFC cathode electron acceptor,MFC will achieve energy simultaneously from waste water and waste gas.In this paper,there were two aspects to improve capacity of MFC.On the one hand,catalysts that were low cost and high catalytic activity should be prepared.On the other hand,the capacity of MFC was tested by replacing O₂ as an electron acceptor with a simulated exhaust gas containing NO.To obtain catalysts with low cost and high catalystic activity,N/Fe co-doped carbon catalyst（N/Fe-DC）was prepared by calcining method.The oxygen reduction performance of N/Fe-DC was understood by electrochemical tests.And it was compared with 20 wt%Pt/C.The results showed that the catalyst activity of N/Fe-DC was closed to 20 wt%Pt/C,and N/Fe-DC had better selectivity and higher stability in neutral electrolyte.When N/Fe-DC was used as MFC cathode catalyst,its maximum power density was 866mW·m^-2,which was 12.3%higher than that of 20 wt%Pt/C as MFC cathode catalyst.In addition,the microstructure characterization of N/Fe-DC,such as morphology,crystal structure and elemental composition,indicated that functional groups（i.e.Fe₃C,Fe-N and pyridinic N）had important influence on the catalytic activity of catalysts.Besides N/Fe-DC,this paper also attempted to prepare N/S/Fe co-doped carbon catalyst（N/S/Fe-DC）.It was found that both NS source and carbon matrix had a great influence on the catalytic activity of N/S/Fe-DC.In this paper,N/S/Fe-DC was prepared by using three different NS source and five kinds of carbon matrix.The activity of these catalysts and the capacity of MFC were compared.The results showed that when the NS source was thiourea（Thi）and the carbon matrix was VXC,N/S/Fe-DC（Thi/VXC）was synthesized,which possessed rich microporous structure and large specific surface area,so it had higher oxygen reduction of catalytic activity,and was better than that of Pt/C.When N/S/Fe-DC was used as MFC cathode catalyst,its voltage was up to 570mV（resistance:1000Ω）,and maximum power density was 868mw·m^-2.Because NO has higher reduction potential,this paper used a simulated exhaust gas containing NO for taking place of O₂ as an electron acceptor.As is known to all,most of the industrial waste gas contains both NO and oxygen,so the mixed gases of NO and O₂that was substituted for air contacted with MFC cathode in this paper.The results showed that when the O₂ concentration was certain,the capacity of MFC increased with the increase of NO concentration.When NO concentration was certain,the capacity of MFC increased with the increase of O₂ concentration.However,when system had only NO,the capacity of MFC was lower than that of O_2.So the capacity of MFC could be improved only if NO and O₂ existed simultaneously.When 10 wt%Pt/C was used as cathode catalyst and NO（1.0%）+O₂（5%）was used for cathode electron acceptor,the maximum voltage and maximum power density of MFC were about 780mV and1127mw·m^-2,which were 32%and 41%higher comparing to using air as electron acceptor.In addition,the capacity of MFC was also improved if N/Fe-DC was used as cathode catalyst and NO+O₂ was used for cathode electron acceptor.MFC could also remove the NO at the same time.Since the cathode area of MFC in this paper is only7cm² and the residence time of gas in the gas chamber is less than 1min,the removal efficiency is very low（7%）.It is known that NO_X through MFC could be transformed into N₂,N₂O,NO₃^--N,NO₂^--N and NH₄⁺-N from the analysis of the components of the exhaust gas.