| With the rapid development of human society,the demand for energy has constantly increased,which inevitably brings problems such as energy shortage and environmental pollution.Microbial fuel cells（MFCs）are capable of utilizing the metabolism of microorganisms to produce electricity during treating wastewater,regarding as an environmentally friendly technology that has attracted widespread attention.At present,the practical application of MFCs is still restricted by the sluggish oxygen reduction reaction（ORR）on the cathode.Although platinum（Pt）has excellent ORR catalytic performance,its high price and poor toxicity tolerance have severely obstructed its large-scale application for MFCs.Therefore,research and development of cathode catalysts with cost-effectiveness,high activity and long-term stability is an effective strategy to break through the bottleneck of practical application of MFC.In this work,based on the point of developing cost-effective cathode catalysts for MFCs,taking nitrogen-doped carbon-based materials as the starting point,cobalt-nitrogen co-doped carbon-based（Co-N/C-x）catalysts and hollow nitrogen-doped carbon nanosphere（HNCNS）catalysts were prepared.Various catalyst characterization methods were used to analyze the structure,morphology and surface chemical properties of catalysts.Electrochemical measurements were used to characterize the ORR activity of catalysts.The catalysts were applied to the cathode of MFCs to evaluate its power generation and wastewater treatment performance.The specific research contents are as follows:（1）One-step pyrolysis of the mixture of melamine and cobalt phthalocyanine（Co Pc）,during which Co and N were co-doped into the in-situ formed carbon support,and the mass ratio of melamine and Co Pc（x=30,50,70,90）was adjusted to prepare Co-N-doped carbon-based（Co-N/C-x）series catalysts,which doping amounts of Co and N on the surface were higher than 2 at%and 18 at%,respectively.The mass ratio x directly affects the catalytic activity of the material.Among Co-N/C-x catalysts,Co-N/C-70 exhibits the highest ORR activity with a half-wave potential of 0.731 V（vs.RHE）and a diffusion control current density of 6.06 m A/cm2 in neutral medium,both of which were better than commercial Pt/C catalysts（0.709 V,4.93 m A/cm2）.MFCs assembled with Co-N/C-70 catalyst achieved a maximum power density of 1190±49 m W/m2,which was slightly higher than that of Pt/C catalyst（1119±3 m W/m2）,and provided high wastewater treatment efficiency（91.9±1.7%）,while the material cost was 60.7%lower than Pt/C,indicating that Co-N/C-70 catalyst has considerable economic benefits and development prospects.（2）Hollow nitrogen-doped carbon nanosphere（HNCNS）catalysts were synthesized with the sacrifice of silica coated carbon nanospheres（CNS@Si O2）as template.Compared with solid silica sphere template,CNS@Si O2 was capable of maintaining hollow structure and enhancing surface chemical properties including increasing the doping amount of N and specific surface area,while pyrolysis temperature（T=800～1100°C）effectively changed the overall performance of HNCNS-T catalysts.HNCNS-1000 exhibited the highest ORR activity in electrochemical measurements,and achieved a maximum power density of 1307±26m W/m2 and wastewater treatment efficiency of 94.0±0.3%applying in MFCs,both of which were superior to that of Pt/C catalyst,while the material cost for power generation was only2.8%of Pt/C.Synthesizing the relationship between nitrogen species or carbon structural defects and power generation of MFCs,carbon structural defects and pyrrolic N were conducive to improve MFCs performance of the catalysts,while graphite N had a negative linear relationship with it. |
