| Fuel cells are representative of energy conversion devices which can directly convert chemical energy into electrical energy.Because of their high energy conversion rate,low pollution,and portability,fuel cells have become the core technology to solve the energy crisis and environmental pollution recently.However,the sluggish kinetic process of oxygen reduction reaction(ORR)in cathode limits the commercial application of fuel cells.Traditional Pt-based electrocatalysts are expensive,poor in stability,and weak in resistance to methanol and CO.Therefore,the search for low-cost,clean,efficient,and stable ORR catalysts has become a hot research topic.After continuous efforts,the ORR activity of non-precious metal catalysts has been greatly enhanced,but still needs to be improved comparing with the commercial Pt/C catalysts.In this article,a series of nitrogen-doped carbon nanomaterials based on transition metals Fe and Co elements were synthesized.The ORR activities of the target catalysts were similar to that of the commercial Pt/C.They are expected to be the promising non-precious metal oxygen reduction electrocatalysts which are alternative to Pt-based electrocatalysts.The main research contents are as follows:(1)Fe/N dual-doped hollow porous carbon sphere nanomaterials:We design a dual template-assisted pyrolysis method to prepare ultra-small Fe3O4 nanoparticles anchored on Fe/N-doped hollow porous carbon spheres(0.010-Fe/N-HNCS-800)for oxygen reduction reaction.The synthesized SiO2 nanospheres which are selected as the hard templet contributed to forming macro-porous structure.F127 is employed to fabricate mesopores through high temperature pyrolysis as a soft templet.By this way,the 0.010-Fe/N-HNCS-800 architecture represents ordered hierarchically porous property with a large BET surface area(1812 m2/g)which can facilitate the mass transport of reactants and increase the electrochemical active area.The Fe3O4 nanoparticles wrapped by graphitic carbon layers provide more active sites and the synergistic interaction between Fe3O4 nanoparticles and doping N has a positive effect on ORR performance.The 0.010-Fe/N-HNCS-800 catalyst outperforms the effective ORR activities with onset potential(Eonset)of 0.96 V(versus reversible hydrogen potential)and half-wave potential(E1/2)of 0.82 V,which is almost the same as the commercial Pt/C(Eonset=0.96 V,E1/2=0.81 V)in 0.10 M KOH.Besides,both the stability and durability of 0.010-Fe/N-HNCS-800 surpass those of the commercial Pt/C.(2)Co/N dual-doped hybrid carbon nanomaterials:ZIF-8,cobalt phthalocyanine,and melamine are selected as precursors,mixed in solution and pyrolyzed at high temperature to synthesize carbon nanotubes wrapped nitrogen-doped hybrid carbon nanomaterials.The Co nanoparticles(NPs)formed at high temperature catalyze the growth of carbon nanotubes(CNTs)in situ from ZIF-8-derived carbon nanomaterials,which are intertwined and connected to form the target catalyst Co@NC-ZM.By comparing the ORR activity of the target catalyst Co@NC-ZM with the NC-ZM and NC under alkaline conditions,we can find that the CNTs catalyzed by Co NPs play a vital role in improving the catalytic activity of carbon materials.The half-wave potential of the target catalyst Co@NC-ZM is positively shifted by 20 mV from the commercial Pt/C and the onset potential is the same as that of the commercial Pt/C.Besides,the target catalyst Co@NC-ZM exhibits excellent stability. |
