Study On The Catalytic Mechanism Of N Doping And KOH Activation On Carbon Materials For The Performance Of Microbial Fuel Cells

Microbial fuel cells?MFCs?are a kind of environmentally friendly biotechnology,which are capable of treating wastewater and simultaneously generating electricity by directly converting chemical energy in organic pollutants into electrical energy.MFCs are catching more and more concerns because of the fact that they can moderate the energy shortages and water pollution.As an innovative and low-energy consumption wastewater treatment technology,MFCs are promising for energy generation and environment remediation.The cathodic oxygen reduction reaction?ORR?has also received much attention as it is an important factor for the power generation in MFCs.Carbon materials catalysts have become a research hotspot due to their superiority in cost.Especially,their ORR catalytic activity can be significantly improved by a series of modifications.First,inexpensive melamine was adopted as nitrogen source to dope nitrogen on cost-effective activated carbon?AC?by pyrolysis.The mass ratio of melamine to activated carbon?N/C?and pyrolysis temperature were optimized to be 10 and 900°C.To clarify the influence of structure and active nitrogen content prepared in different preparation conditions on the ORR performance,a series of experiments?scanning electron microscope,Brunauer-Emmett-Teller,X-ray photoelectron spectroscopy and rotating disk electrode?were carried out.A good agreement between the content of pyridinic N and high ORR activity was observed.As a dominant four electron cathode catalyst,AC-N10-900 exhibited the best performance both in electrochemical and MFCs tests compared with AC and Pt/C.The maximum power density was 1042±35mW m^–2,which was 65.4%and 116.2%higher than that of AC and Pt/C,respectively.Next,N-doped carbon aerogel?CA?was prepared by one-pot template-free synthesis and chemically activated with potassium hydroxide?KOH?.KOH activation significantly increased the BET surface area and hierarchically porous structure?especially micropores?and also influenced active nitrogen species as well as oxygen functional groups?C-O-C and COOH?content.Pyridinic N content increased with KOH increasing,while pyrrolic N content decreased.ORR activity showed a positive linear correlation with pyridinic N content;however,it decreased with pyrrolic N content increasing.C-O-C and COOH content increased after activation,and then decreased with KOH increasing.The reduced C-O-C and COOH content of CA-KOH guaranteed a lower H₂O₂ yield for higher MFC efficiency.CA-10KOH?mass ratio of KOH to CA was 10?exhibited outstanding performance with a maximum power density of 967±34 mW m^–2,which was 37.4%,55.2%%and 283.7%higher than platinum?Pt/C?,AC(BET surface area of 2276 m² g^–1)and CA,respectively.Apart from this,CA-10KOH also presented the highest COD removal?86.9±1.8%?,which was 15.1%,19.9%and 9.8%higher than AC,Pt/C and CA,respectively.The outstanding ORR catalytic performance of CA-10KOH was attributed to the conjunct effect of superior BET surface area(1827 m² g^–1),increased micropores,the highest pyridinic N?0.26 at.%?,the lowest pyrrolic N content and reduced C-O-C and COOH content.Overall,AC-N10-900 and CA-10KOH,as low-cost metal-free cathode ORR catalysts,are promising for the practical application in MFCs.