Biomass-derived Self-doped Carbon Materials As High-performance Electrode Materials In Microbial Fuel Cells

Microbial fuel cell?MFC?is a new technology extracting electricity from organic compounds in wastewater by using bacteria as catalysts.However,the low power output of MFC hinders its practical application in wastewater treatment.Electrode material is critical in affecting the power output;therefore,many efforts have been made to synthetize or modify carbon-based electrode materials that enhance the power output.Nevertheless,these methods are heavily relied on the use of chemicals as carbon sources,and the addition of heteroatom-doped agents,active agents or templates,thus resulting in the increase in the costs and the environmentally unsustainability.The biomass is a predominantly carbonaceous material,and also rich in other heteroatoms?i.e.,N,P,and S?;this makes it possible to obtain self-doped carbon derived from the biomass using pyrolysis.The obtained carbon should hold the potential for application in MFCs as cost-effective electrode materials.In recent years,substantial attention has been given to anode modifications that enhance surface area and functional groups of carbon-based anode materials,in order to improve bacterial adhesion and electron transfer from microbes to the anode.The first effort of this study was made to obtain the municipal sludge-derived carbon?SC?with a porous structure and abundant surface functional groups through simply pyrolyzing the municipal sludge.The SC is then coated on the 3-D graphite felt?GF?surface by pyrrole electropolymerization,resulting in the formation of PPy/SC-GF anode.The results indicate that the PPy/SC-GF can substantially increase anode surface area,surface N/C ratio and higher relative contents of O=C-NH2 and O=C-O functional groups than other counterpart anodes.These characteristics are essential for increasing bacterial attachment to the anode surface,electron-transfer rate and thus anode performance and power performance.The maximum power density resulting from the PPy/SC-GF anode was 568.5 mW m^-2,increased by 1.9,2.7 and 3.5 times as compared to the PPy/AC-GF anode,the PPy-GF anode and GF anode,respectively.Oxygen reduction reaction?ORR?catalyst is the core part of cathode in MFCs.The second attempt of this study was made to prepare the mesopourous Fe-N-C electrocatalysts from the living Fe mineral@bacteria encrustation?which is formed as a consequence of anaerobic incubation between Shewanella oneidensis MR-1 and Fe minerals.?without the use of activation agents or templates.The living Fe mineral@bacteria encrustation-derived carbon pyrolyzed at 800 ??Fe@BC-800?displayed outstanding electrochemical activity for ORR in all-pH media.In alkaline media,the Fe@BC-800 exhibited an onset potential of 1.01 V with a half-wave potential of 0.85 V;both values are more positive than those related to the commercial Pt/C catalysts.In neutral and acidic media,these values were slightly negative but still comparable to those obtained from Pt/C catalysts.The physicochemical characterization results indicate that the resulting high surface area,high conductivity,abundance in Fe-N-C,pyridinic N,and graphitic N moieties,and heteroatom dopings explained the superior activity.The MFC equipped with the newly developed Fe@BC-800 cathode achieved a maximum power density of 1926.7 mW m^-2,an increase of 134.5% relative to that obtained from the Pt/C cathode,indicating the great potential for practical application of this material in fuel cells.These results demonstrate the potential to use this easily formed biomass for the preparation of high-performance carbon electrocatalysts as an attractive alternative to Pt/C for ORR.