| With advantages of high energy density,safety and low cost,Zn-air battery challenges the dominant position of lithium ion battery and is an ideal next generation energy storage device.The slow reaction kinetics in cathode causes that the usage of the catalyst has become inevitable.The most efficient catalyst is still noble metal catalysts,but its scarce reserves,high costs and poor stability in alkaline electrolyte greatly hinder the industrialization path of zinc air battery.Thus the development of stable,low cost,high efficient non-noble metal ORR/OER bifunctional catalyst is significant.Herein,the OER catalytic activity of transition metal/N co-doped carbon material with excellent ORR activity is improved through different measures.The main research contents are as follows:（1）The high temperature pyrolysis is used to prepare Fe/N co-doped carbon（Fe NC）materials,and the Fe3C generated during the preparation process is used as the iron source to guide Ni Fe2O4anchoring to the specific position of Fe NC to obtain Ni Fe2O4/Fe NC-0.4through hydrothermal reaction and low temperature heat treatment,which can enhance the OER activity of Fe NC and ensure the exposure of the active site on Fe NC at the same time.Due to this special structure and the existence of highly active sites such as Fe N4,Fe particles and N-doped carbon,the half-wave potential of Ni Fe2O4/Fe NC-0.4 reaches 0.83 V and the reaction process is a quasi-four-electron process.In addition,the catalytic activity of OER is greatly improved by Ni Fe2O4and the synergistic effect between Ni Fe2O4and Fe NC.The OER potential of Ni Fe2O4/Fe NC-0.4 at 10 m A cm-2is only 1.54 V.The voltage difference of charge-discharge platform in the Zn-air battery only increases by 0.19 V after cycling for 100 h at 10 m A cm-2,which is much lower than 1.28 V of Pt/C+Ru O2.NiFe2O4/FeNC-0.4 exhibits excellent ORR/OER bifunctional catalytic activity and stability.（2）With Co/N co-doped carbon material（CoNC）as the carrier and Co metal growing during the preparation of CoNC as the Co source,FCN LDH-FNCO/CoNC composite is prepared by one-step hydrothermal.The Co metal guides the Fe/Ni co-doped Co3O4and the FCN LDH containing three type transition metal elements（Fe CoNi）to be loaded on the specific position of CoNC.Due to the special structure,the high activity of Fe/Ni co-doped Co3O4and the existence of CoN4,N doped carbon and Co particles,FCN LDH-FNCO/CoNC-1.0 exhibits excellent ORR catalytic activity and its half-wave potential reached 0.86 V,which is the same as commercial Pt/C.In addition,synergistic effect also exists between FCN LDH and CoNC,which greatly improves the OER catalytic activity.The OER potential of FCN LDH-FNCO/CoNC-1.0 at 10 m A cm-2is only 1.50 V.The voltage difference of charge-discharge platform in the Zn-air battery only increases by 0.20V after cycling for 50 h at 10 m A cm-2,which is much lower than 0.94 V of Pt/C+Ru O2.The FCN LDH-FNCO/CoNC-1.0 shows excellent ORR/OER bifunctional catalytic activity and stability. |
