The Research Of Transition Metal Loaded Carbon Bifunctional Electrocatalyst In Zinc-Air Battery

The development of green energy such as wind energy,solar energy and hydropower is in the ascendant.But the renewable resources are limited by region and time while being made.Therefore,we urgently need low-cost and large-capacity energy storage devices to store these green energy.Rechargeable Zinc-air batteries（ZABs）have becoming the focus of the new generation of energy storage research for its advantages of low cost,excellent safety,clean and high energy density.The commercialization of rechargeable ZABs were limited by poor cycle stability,low discharge power,especially the sluggish kinetics of oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）on the air cathode.The commercialized ORR/OER catalysts are still mainly Pt based,Ru based and Ir based.However,the widespread application of ZABs is impeded by catalysts’lack of bifunctional catalytic activity,high price and poor electrochemical stability.Thus,it is an urgent target to develop ORR&OER bifunctional catalyst with high catalytic activity,good electrochemical stability and low cost.Transition metal-based catalysts have the advantages of low price,stable properties,green environmental protection,bifunctional of ORR&OER and high catalytic potential,which make them become the hot research materials for the catalysts of ZABs at present.The transition metal particles loaded carbon base supporter can have the advantages of transition metal-based catalysts.And the catalytic activity area was further improved,the electrochemical stability was increased,the conductivity and the ORR activity were optimized for it is improved on the basis of transition metal based materials.However,the exposed transition metal particles are still easy to be corroded,and the general loading method will also generated the oversize particles,resulting in poor performance and instability of the catalyst.In this paper,the unique structure of CNT encapsulate transition metal particles is designed.The structure can inhibit the formation of larger particles and protect the inner metal from corrosion,improving the electrochemical activity and stability of the material.On this basis,through the reduction and evaporation of Zinc,the electrochemical active surface area（ECSA）of the material was increased,which improved the nano-structure of the sample and further improved the catalytic activity of the material.Meanwhile,the activity source of ORR&OER catalyst and its application in ZABs were also investigated.And the main research contents are as follows:（1）FeCo alloy particles encapsulated in nitrogen-doped CNTs（FeCo@NCNT）as a bifunctional catalyst for the air cathode of ZABs.FeCo@NCNT was prepared by pyrolysis precursor at high temperature in nitrogen atmosphere,which is consist of melamine,chitosan and chloride of iron and cobalt as carbon,nitrogen and metal sources.It was confirmed by comparison that the metal particles encapsulated in nitrogen-doped carbon nanotubes were the main active sites of ORR,and FeCo alloy particles were the main active sites of OER.The prepared samples show excellent bifunctional electrocatalytic performance.The half-wave potential of ORR(E_1/2)is0.845 V,and the potential of OER(E_j=10)is 1.527 V,which is better than the commercial noble metal catalyst.The bifunctional catalytic performance(ΔE=E_j=10-E_1/2)is 0.682 V.While the ZAB reached a high open circuit voltage of1.491 V and a peak power density of 120 m W cm^-2.And it retained its original catalytic activity after the charge-discharge cycle exceeded 100 h.（2）Porous nitrogen-doped carbon matrix supported FeCo particles（Zn/Feco-950）as air cathode catalyst for ZABs.Zinc,which is easy to evaporate,was introduced to further increase the ECSA of sample to obtain Zn/FeCo-950.In the process of increasing ECSA,the proportion of active components of the material can be increased.It can improve the catalytic performance and maintain the electrochemical stability of the material also.E_1/2 of ORR is 0.866 V,E_j=10 of OER is 1.516 V,ΔE=0.650 V.The assembled ZAB has an open circuit voltage of 1.494 V and can stably charge and discharge over 100 h.