Fe/Co Anchored N-doped Hollow Nanospheres For Efficient Electrocatalytic Oxygen Reduction Reaction And Rechargeable Zn-air Battery

Fuel cell is a high-efficiency energy conversion device.It can reach a conversion efficiency of 60%in the process of converting fuel into electricity,and is not restricted by the Carnot cycle.It is a very promising new kind of battery.Due to the high energy barrier of its cathodic oxygen reduction reaction(ORR),the currently used Pt/C catalysts cannot be commercialized on a large scale.Therefore,efficient and economical catalysts are urgently needed.Non-precious metal carbon-based catalyst is a catalyst that is expected to replace commercial Pt/C.It has lower cost,and the internal active sites can be fully utilized.In addition,carbon-based catalysts can be additionally doped with active elements,such as N,S,etc.to further improve its catalytic activity.This article aims at the above research results,uses the hard template method as a guide,and uses polyaniline(PANI)core-shell microspheres as precursors to synthesize Fe,Co,N ternary components Co-doped carbon hollow microspheres.Its electrochemical catalytic activities and application in Zn-air batteries were studied.In this method,the precursor NDHC is first synthesized,and then grown in situ and carbonized to form Fe/Co@NDHC microspheres.After research and characterization of the synthesis process,it was found that Fe-C,Co-C and pyridinic-N active sites may be formed.In order to further determine the doping state of the three active sites,the density free function(DFT)was used to calculate the change of the free energy of the oxygen reduction reaction under different active site doping conditions.The practical result is co-doping of three-phase active sites.Further characterization revealed that this hollow structure has a large specific surface area.The prepared Fe/Co@NDHC has highly dispersed active sites of Co-C,Fe-C and pyridinic-N.When testing its oxygen reduction potential in alkaline electrolyte,an excellent ORR activity was observed,with onset potential(E0)of 1.0003V and half-wave potential(E1/2)of 0.9183V,which is better than that of commercial 20 wt%Pt/C(E0:1.02V,E1/2:0.86).In addition,compared with the Pt/C alkaline electrolyte system,excellent methanol resistance and long-term stability were also observed in Fe/Co@NDHC alkaline electrolyte system.Moreover,the prepared Fe/Co@NDHC also has good OER performance(1.56V).When used as the cathode of a zinc-air battery,Fe/Co@NDHC exhibits excellent discharge voltage(1.2V),specific capacity of 564 mAh g-1Zn,and energy density of 85 mW cm-2.It can be speculated that this outstanding performance of Fe/Co@NDHC can be attributed to the unique double-shell porous graphene structure and the synergistic effect of Co-C,Fe-C and pyridinic-N active sites.