Study On Preparation And Electrochemical Properties Of MnO/M(M=Fe,Co,Ni)Composite Catalyst

The metal-air battery uses oxygen in the environment as the cathode reaction material,which has the advantages of high energy density,stable discharge and low cost.Air-electrode is an important part of metal-air battery.Oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）are carried out on the solid-liquid-gas three-phase interface of the electrode,and ORR and OER catalysts play an important role in it,which determines the dynamic performance of air electrode and the quality of air battery.As a traditional ORR catalyst,manganese oxide（MnOx）has many advantages,such as abundant resources,friendly environment,rich crystal form and so on,Its disadvantage is that its ORR catalytic performance is poor and almost no OER performance,which is difficult to meet the increasingly stringent requirements for air battery catalysts（high catalytic activity,bi-functional,etc.）.In this article,bimetallic organic framework（MOF）MIL-100 was prepared by solvothermal method,and then MnO/M（M = Fe,Co,Ni）/C was obtained by calcination with different metal reduction potentials,composite catalyst is expected to improve its catalytic performance through the formation of many "solid-solid" heterogeneous interfaces between MnO / M and the high dispersion in carbon matrix,so as to obtain a bifunctional（ORR and OER）catalyst with excellent catalytic performance.The main work and research contents of this paper are as follows:1.Mn/Fe-MIL-100 precursor was prepared by solvothermal method.The effects of solvothermal reaction time and temperature on the particle size and morphology of Mn/Fe-MIL-100 precursor were studied and compared.The results showed that regular polyhedron with average particle size of about 300 nm could be obtained when the reaction time was 6 h and the reaction temperature was 125℃.By optimizing the calcination temperature and time,the MnO/Fe/C composite catalyst was calcined at 800℃ for 8 h.As a contrast,was prepared by the same process MnO/C and Fe/C catalyst.The electrochemical performance test showed that MnO/Fe/C,the ORR limit current density of C is 6 m A cm^-2,more than the Pt/C of catalyst 5.7 m A cm^-2;OER performance at a current density of 10 mA cm^-2.The overpotential is 0.351 V,slightly lower than Ir O2 of 0.318 V.Both of them are much better than those of MnO/C and Fe/C,showing good bifunctional catalytic performance and development potential;2.MnO/Co/C and MnO/Ni/C composite catalysts were prepared by the same process using Co and Ni instead of Fe.Compared with MnO/C,the ORR and OER catalytic performance of MnO/Co/C and MnO/Ni/C were significantly improved.The ORR limiting current density of MnO/Co/C and MnO/Ni/C were 5.3 and 5.4 m A cm^-2.When the current density of OER was 10 m A cm^-2,the overpotential of MnO/Co/C and MnO/Ni/C were 0.364 V and 0.366 V.The results show that MnO/Fe/C has the best catalytic performance;3.MnO/Fe/C catalyst was used to prepare air electrode,and a simple rechargeable zinc-air battery was further formed.The test results show that the self-made zinc-air battery has a stable open circuit voltage（OCV）of 1.43 V,which is basically equivalent to 1.41 V of Pt/C ||IrO₂,and is consistent with the reported open circuit voltage range of zinc-air battery.When the current density is 10 m A cm^-2,the specific capacity is 700 m Ahg Zn^-1,the corresponding energy density is 896 Wh Kg Zn^-1,and the peak power density is 120 m W cm^-2.However,the cycling test results show that the self-made zinc-air battery has poor cycling performance.After 25 cycles,the energy efficiency is reduced to 50%.The analysis shows that this is related to the electrode preparation process,which needs to be further improved in the follow-up work.