Enhancement Of The Oxygen Reduction Electrocatalyst Activity Of Nitrogen And Phosphorus Co-doped Carbon In The Cathode Of Microbial Fuel Cells

Microbial fuel cell?MFC?is an electrochemical device that converts chemical energy into electrical energy based on the metabolically oxidizing organic matter of electroactive microorganisms.The chemical energy of waste organic matter in sewage can be converted into available electric energy by MFC.Therefore,it has the dual functions including decontamination and production capacity,which attracted the attention of researchers in the recent years.The cathode is not only one of the key components that determine the performance of MFC,but also one of the factors limiting the industrialization of MFC technology.Due to the abundant of oxygen content in the air,the oxygen reduction reaction?ORR?is the most important cathodic reaction of MFC for wastewater treatment.ORR has relatively low reaction kinetics which leads to require the use of an ORR catalyst.Pt/C and other precious metals have excellent ORR catalytic properties.but However,the expensive price limits its large-scale application in MFC.Therefore,the development of low-cost,high-performance ORR catalysts is one of the key issues that need to be solved in order to promote MFC in actual wastewater treatment applications.Nitrogen-phosphorus co-doped carbon?NPC?is an excellent ORR catalyst because of heteroatom doping which changes the electronic distribution of carbon atoms and has excellent ORR catalytic properties.The high specific surface area of the catalyst would increase the active catalytic sites,while the high conductivity would increase the electron transfer efficiency.In order to further improve the ORR catalytic performance of NPCs,two methods of improving the specific surface area and conductivity were used to optimize the catalytic performance of NPC for oxygen reduction.The main research content is as follows:?1?Carbon black?CB?is often used to increase the electrical conductivity of electrode materials due to its excellent electrical conductivity.In this study,the ORR catalytic performance of the NPC was improved by using CB as conductive fillers to increase the conductivity.In this paper,polyaniline doped with phytic acid was supported on CB by in-situ oxidative polymerization,and then nitrogen-phosphorous co-doped carbon modified carbon black?NPC@CB?was prepared by pyrolysis at high temperature.Experiments optimized the mass ratio of NPC to CB to obtain an optimal ratio catalyst?NPC@CB-0.4?.The prepared catalyst NPC@CB-0.4 has a high specific conductivity and higher the degree of graphitization than that of single element doped carbon NC@CB and PC@CB.In the neutral solution,the highest ORR catalytic activity was exhibited for the onset potential and the current density.The MFC prepared by NPC@CB-0.4 as an ORR catalyst has an open circuit voltage of 0.756 V and a power density of 1209 mW m^-2,and its power density is more than twice that of the ORR catalyst MFC prepared by pristine CB.In practical applications of MFCs,NPC@CB-0.4 can be used as a low cost,high-efficiency ORR catalyst.?2?Activated Carbon?AC?is an environmentally friendly ORR catalyst.Due to its mesoporous properties,high specific surface area and its adsorption properties,it has been widely used in microbial fuel cells.However,pristine AC exhibited a high over-potential in the ORR catalytic process and the electro-catalytic activity was not high.The NPC@AC composite catalyst was prepared by replacing CB with AC in the same manner as in the previous section.Because of AC can adsorb nitrogen and phosphorus precursors and increase the heteroatom content of the catalyst,the initial potential of the catalyst is shifted positively,thereby enhancing the catalytic performance of the catalyst.The optimal ratio catalyst?NPC@AC-0.7?was obtained by NPC and AC mass ratio optimization experiments.Compared with pure AC,NPC@AC-0.7 retains the high surface area of AC and low ORR overpotential of NPC.It shows better electrocatalytic activity in neutral solution and even better catalytic performance than pure NPC.Microbial fuel cells with air cathodes as cathodes prepared with NPC@AC as ORR catalyst have higher open circuit voltage and power density of 0.753 V and 1223 mW m^-2,respectively,which is much higher than that of pure AC(0.432 V and 595 mW m^-2).In practical use of MFCs,NPC@AC-0.7 can be used as an efficient ORR catalyst.