Interface Control And Performance Evaluation Of Carbon-based Air-cathode Catalysts For Microbial Fuel Cells

Microbial fuel cell(MFC)is an emerging wastewater treatment technology that can generate electricity from organic matters and purify wastewater simultaneously.Cathode performance and costs are the main challenges that restrict MFC development.Therefore,developing cheap,efficient and sustainable cathode catalysts is crucial to large-scale applications for MFCs.Based on carbon-based air-cathode catalysts,specific surface area,electrical conductivity,and surface functional groups were examined for their influence on the performance of electricity production.The methods and types of element doping were further optimized for surface and interface control to improve the electrocatalytic performance of difference carbon based catalysts,and thus to enhance the MFC performance.Activated carbon was used as an air-cathode catalyst for interface control,and the effects of specific surface area,surface active functional groups,and electrical conductivity on the MFC power generation were investigated.Activated carbon particles with different sizes and superfine powdered activated carbon were prepared via ball milling and pulverizing technology.The relationship between the specific surface area and catalytic properties of activated carbon was investigated.N-doped activated carbon was synthesized by ball milling to increase active sites,and activated carbon and carbon black composite carbon catalyst was proposed to enhance the electrical conductivity.High specific surface area,high conductivity,and multiple active sites were determined to be the key characteristics of carbon-based MFC air-cathode catalysts.Carbon nanotubes are carbon materials with high specific surface area and high conductivity,and were used as air-cathode catalysts for interface control.Chemical vapor deposition(CVD)and ball milling were applied to develop N-dope carbon nanotubes with high catalytic performance.Via the method of secondary deposition,a new type of carbon nanotubes,a carbon coaxial nanocable with surface enriched nitrogen was developed.The nitrogen active sites were fully exposed and the MFC power density was significantly improved,54%higher than that of the normal N-doped carbon nanotubes.Graphene is also a carbon material with high specific surface area and high conductivity,and was also used as an air-cathode catalyst for interface control.Graphene based catalysts were prepared by chemical vapor deposition and ball milling,respectively,and N element doping was achieved at the same time.By optimizing the growth parameters of N-doped graphene,a proof-of-concept for the binder-free N-doped graphene air-cathode was proposed.The substrate for graphene growth was directly used as a current collector,without etching,and the internal resistance of the air-cathode was significantly decreased.N-doped graphene was also synthesized by ball milling using graphite powders as precursors,and pyrrole as nitrogen source.Single-type doping of nitrogen element was achieved for directional interface control.Based on the optimized ball milling method,three typical carbon-based materials including activated carbon,carbon nanotubes,and graphene were used for electrocatalyst interface control.The effects of doping of Fe and Co and the co-doping of Fe-N and Co-N on catalytic performance were investigated respectively.Fe/Co-N-C bonding during heat treatment was the key factor to improve the surface active sites of carbon materials.Moreover,the surface functional groups of these three typical carbon-based materials were compared during the modification.AC-N-Fe-H was developed as the best air-cathode catalyst and the maximum power density reached 2390 mW/m~2.