| Microbial fuel cell(MFC)is a new type of environmental protection device which uses microorganisms as biocatalysts to convert soluble organic matter into electricity.Oxygen reduction reaction(ORR)is an essential cathode reaction in many important energy conversion devices.Platinum-based catalysts usually have the highest ORR activity due to their optimal binding energy of oxygen intermediates.However,the high cost and scarcity of platinum is an obstacle to the large-scale application of proton exchange membrane fuel cells in the energy field.To overcome this problem,the development of cheap and efficient platinum-group metal-free(PGM)ORR electrocatalysts has been considered as a potential strategy to reduce production costs.In this paper,a series of Fe-based Fe(x)@N-C(x is the mole ratio of Fe/PTA),Fex-N-C@TABOH(x is different iron loads)and Fe@N5-C catalysts were prepared by different methods.The catalysts were characterized by XRD,XPS,BET,TEM and SEM.CV,LSV and EIS were used for electrochemical tests.The effects of different catalyst loads on the electric performance of microbial fuel cells with single chamber air cathode were studied.Important results are shown as follows:(1)The MIL-53(Fe)-N catalyst precursors were prepared by a one-step hydrothermal method using cheap acetonitrile as nitrogen source.Then,Fe(x)@N-C catalyst with different Fe contents were prepared by pyrolysis of MIL-53(Fe)-N in N2 atmosphere.The effects of Fe dosage on the structure,electrochemical performance and electricity generation performance of MFC were investigated.Among Fe(x)@N-C catalysts,Fe(0.3)@N-C catalysts showed the best ORR performance.The maximum open-circuit voltage is 0.60 V,close to Pt/C MFC(0.61V),the power density is 604.6 mW·m-2,and the output voltage is stable at 0.58 V,which is much higher than that of commercial Pt/C catalyst.(2)Porous nitrogen-containing carbon Fex-N-C@TABOH(x with different Fe loading capacities)was prepared with Fe/Zn-ZIF as the precursor and tetrabutylammonium hydroxide(TAB OH)as the template agent,and was converted into structured FeN/C electrocatalysts.Among all prepared composites,Fe4-N-C@TABOH has the largest specific surface area and pore volume,as well as the most Fe-Nx active centers.The power density of Fe4-N-C@TaBOH in MFC is 830.1 mW·m-2,close to the power density of commercial Pt/C(933.8 mW·m-2),and the output voltage is stable at 0.67 V.(3)Fe@N5-C composites with FeN5 active sites were prepared by anchoring FePc molecules to pyridine-functionalized graphene using iron phthalocyanine as iron and nitrogen sources.Fe@N5-C catlyst obtained after carbonization at 800℃ had the best performance.The initial potential of Fe@N5-C is 0.84 V,which is close to that of commercial Pt/C(0.89 V).The limiting current density is-5.24mA-cm-2,and the internal charge transfer resistance is 11.3 Ω.The maximum power density of the catalyst applied to MFC was 859.0 mW·m-2,slightly lower than the maximum power density of the commercial Pt/C catalyst(933.8 mW·m-2). |
