Study On Catalytic Performance Of Nitrogen Doped Carbon Supported Non-noble Metal Catalysts For Oxygen Reduction Reaction

The cathodic oxygen reduction reaction is one of the key steps determining the efficiency of the fuel cel.Searching for efficient non noble metal catalysts as a substitute is the research focus in this field.In this paper,with the preparation of nitrogen doped carbon supporting non noble metal catalysts,the relationship between the structures and ORR catalytic performance in alkaline condition was investigated.At first,a series of nitrogen doped carbon supported Fe catalysts were prepared via simple once-impregnation and pyrolysis methods,with hematin as precursor and different carbon materials as carriers.By the means of XRD,XPS,Raman and etc,the effects of precursor content and carrier types on the catalyst structure and properties are systematicaly studied.It was found that when the mass fraction of Fe in the precursor/carrier was equal to 4%,the as-prepared catalyst exhibited the best catalytic activity(E_onset=-60mV,E_1/2=-170mV,vs Ag/AgCl)and 4e selectivity.Under the same preparation conditions,the catalyst with graphene and carbon black as carriers showed more efficient catalytic performance than that with carbon nanotube as carrier.Then,using biological small molecule dopamine as a nitrogen source and transition metal nitrates or acetate as metal precursors,a series of nitrogen doped carbon nanotubes supported transition metalcatalysts were prepared via one pot method.It was found that the catalytic activity was affected by graphitization degree and nitrogen content,and the selectivity was affected by the existence forms of metal.Among them,catalyst with Mn loading exhibited the best ORR catalytic performance(E_onset=-100mV,E_1/2=-170mV,vs Ag/AgCl).But catalysts with Fe and Ni loading exhibited low ORR activity and 4e selectivity due to the lower graphitization and nitrogen contents,and also elemental metals existing.Finally,nitrogen-doping CNT supported Fe catalysts were prepared by twice-impregnation and high-temperature pyrolysis method.The effects of nitrogen source and second pyrolysis temperature on the structure and ORR performance of the catalysts were studied.It was found that total and active speices content of N increased by using dopamine and 1,10-phenanthrine respectively as first and second nitrogen resources and pyrolysis at the temperature of 600oC.Compared with catalysts synthesized by one-pot,the E_1/2 shifted 123mV positively and the electron transferred number increased from 3.14 to 3.75.