Preparation And Electrocatalytic Performance For ORR Of Transition Metal Catalysts

As the main energy source in the world,the reserves of fossil fuels are dwindling,and the environmental impact caused by using fossil fuels is becoming increasingly serious.Therefore,the key to solve this problem now lies in finding effective,clean and renewable energy substitutes.For natural energy,such as solar energy,although the use process is clean and non-pollution,and it is inexhaustible renewable energy,but the use of such energy is restricted by natural conditions,resulting in unstable energy output.In order to make energy output continuous and stable,energy storage and conversion devices must be considered.As an energy conversion device,fuel cell which is clean and efficient has attracted much attention of researchers.The sluggish kinetics of ORR is a major problem that hinders the development and large-scale commercial applications of fuel cells.Platinum-carbon catalyst,which is recognized as a highly efficient catalyst for ORR,is not only scarce and expensive,but also has poor stability and methanol tolerance.Therefore,the development of low-cost,simple,efficient and stable non-noble metal catalysts have become a research hotspot in recent years,which is of great significance to the development of fuel cells.Therefore,in this paper,the following three different transition metal ORR catalysts were prepared with simple methods using cheap and easily available raw materials:(1)Fe was mixed into the precursor by the complexation between phenanthroline and ferric chloride,dimethylimidazole and g-C3N4 were used as carbon and nitrogen sources,and Fe@N-C catalyst was obtained by high-temperature pyrolysis.After adjusting the ratio of phenanthroline to ferric chloride and the pyrolysis temperature of the precursor,the obtained Fe@N-C/800 had the best ORR performancein in the alkaline medium(E1/2=0.85 V(vs.RHE),JL=9.44 mA/cm2),which attributed to the presence of Fe-N active sites possiblly.(2)Mesoporous CoNi-N-C/800 catalyst co-doped with Co,Ni bimetal lic and N was prepared by impregnation and high-temperature pyrolysis method using glucose as carbon source,metal chloride as metal source and urea as nitrogen source.The formation of alloy nanoparticles and th e possible Co-N active sites were the main reasons for the better ORR performance of CoNi-N-C/800 in the alkaline medium(E1/2=0.81 V(vs.RHE),JL=4.81 mA/cm2).(3)The FeCoNi@NC catalyst was obtained by simple high-temperature pyrolysis of the precursors.The performance of the catalyst was optimized by adjusting the metal proportion in the precursors and the pyrolysis temperature.The optimized FeCoNi@NC/800 had better catalytic activity,stability and methanol tolerance than 20%Pt/C in 0.1 M KOH(E 1/2=0.91 V(vs.RHE),JL=6.15 mA/cm2),which might attribute to the synergistic of three metals and the synergistic catalysis of FeCoNi alloy nanoparticles with nitrogen-doped carbon shells.