| With the rapid development of society,human demand for energy has increased year by year,and many environmental problems that cannot be ignored are brought:water pollution and air pollution.At this time,microbial fuel cells(MFCs)capable of outputting electrical energy while treating sewage have received widespread attention due to the role of transforming waste for treasure.At present,the power generation performance of MFCs is mainly affected by the performance of the cathode oxygen reduction.Although traditional Pt/C is considered to be the best oxygen reduction catalyst,Pt/C will perform rapid performance degradation in the application of neutral MFCs,and Pt has the disadvantages of low reserves and expensive prices.Therefore,the development of a low-cost,efficient,and stable catalyst based on the abundant elements of the earth to replace Pt/C cathode has become the main research direction for improving the performance of microbial fuel cells.In this work,based on non-metal heteroatom-doped carbon materials and iron-nitrogen-carbon synthesis routes,starting from the low-cost carbon black(Vulcan XC-72R),the nitrogen-doped carbon black series(CN-X,X is pyrolysis temperature,X=700,800,900,1000℃)and further improved iron-nitrogen doping carbon black series(C-Nx-Fe,x is the mass ratio of nitrogen source to carbon black,x=1,3,5,7,9)were synthesized.Various material characterization techniques were used to analyze the structure and surface chemical information of catalysts.Electrochemical analysis methods were used to characterize the oxygen reduction activity of catalysts,and the wastewater treatment efficiency of catalysts in MFCs was studied.The specific research contents are as follows:(1)A low cost,efficient and stable CN-X catalyst was obtained through the synthesis route of doped nitrogen after carbon black pretreatment with concentrated sulfuric acid,and the effect of pyrolysis temperature(700-1000℃)on the catalytic activity of catalysts was studied.The increase of pyrolysis temperature changed the structural characteristics and nitrogen content of catalysts and promoted the conversion of pyridine nitrogen and pyrrole nitrogen to graphite nitrogen.The electrochemical characterization results showed that CN-800 had the best catalytic activity for oxygen reduction.The microbial fuel cell loaded with CN-800 cathode had the highest voltage output(382-411 m V),sewage treatment efficiency(77.2±1.5%)and the maximum power density(371±3 m W/m~2),and the cost of power generation was about half that of Pt/C cathode.According to the relationship between different nitrogen species and maximum power density,pyridine nitrogen can improve the power generation performance of catalysts in neutral MFCs wastewater treatment.(2)Based on the research of CN-X,the iron-nitrogen doped carbon black(C-Nx-Fe)catalysts were synthesized by replacing the nitrogen source with cheap urea,reducing the urea input,and adding low amount of ferrous acetate.Studied the effect of the mass ratio of urea to carbon black on the oxygen reduction activity of catalysts,and the catalyst loading(1,2,3,4mg/cm~2)on the performance of C-N5-Fe in MFCs.Various characterization analyses showed that the oxygen reduction activity of C-Nx-Fe catalysts was significantly improved compared to CN-X.C-N5-Fe catalyst had the best catalytic activity due to the better synergistic catalysis formed between the highest pyridinic nitrogen content and higher Fe doping.During the 1200h operation,the C-N5-Fe cathode with a loading of 3 mg/cm~2 had a maximum power density of 390±10 m W/m~2,a voltage drop of about 1%,while the power generation cost was only20.5%of CN-800,proving that C-N5-Fe is a more cost effective and stable cathode catalyst.In addition,the 2 mg/cm~2 CB-N5-Fe cathode showed better catalytic efficiency for oxygen reduction with maximum power density and wastewater treatment efficiency of 424±3 m W/m~2and 82±1%,respectively.And its output voltage had almost no attenuation.The loading of 2mg/cm~2 can better perform oxygen reduction catalytic performance of C-N5-Fe while reducing operating costs in MFCs.Therefore,the low-cost,effective and highly stable C-N5-Fe cathode catalyst is expected to be used in MFCs treating wastewater. |
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