Preparation And Properties Of Two-dimensional Transition Metal/Carbon Based Cathode Materials For Zn-Air Battery

Nowadays,the development of zinc-air battery is mainly restricted by the slowly kinetic processes of oxygen reduction reaction and oxygen evolution reaction at the air cathode.Therefore,exploitation of high-efficiency,low-cost and durable bifunctional catalyst has great significance and value for the practical application of zinc-air battery.Our article focuses on the two-dimension transition metal/caebon-based catalyst.The outstanding bifunctional ORR/OER two-dimension transition metal-based graphene/graphene like nanosheets are synthesized by means of morphology design,regulation catalyst composition and construction of dual-metal sites.The research details are as follows:1.The iron based two-dimension ultrathin graphene like nanosheets（Fe/GNS-1.5）are synthesized through the Na Cl template method with the glucosamine as carbon source and ferric nitrate as metal source.The influence of metal content and metal types on morphology,structure and performance to prepared material are analyzed.SEM and TEM images show that when the ratio of metal source to carbon source is 1.5,the Fe/GNS-1.5 presents unique ultrathin graphene like structure.During heat treatment progress,the NO₃^-anions are decomposed and release a large amount of gas,which play a key role on nanosheets exfoliation and pores formation.The electrochemical measurement shows that Fe/GNS-1.5 exhibits excellent ORR performance.However,the OER catalytic activity of Fe/GNS-1.5 is poor.What’s more,the Fe/GNS-1.5 based zinc-air battery displays good battery performance with the large power density(156 m W cm^-2),high specific capacity(807m Ah·g^-1)and durable cycling stability（more 600 cycles）.2.To improve the OER activity of iron-based graphene like catalyst,we prepared Fe Ni nanoparticles uniformly dispersed graphene like nanosheets by introducing nickel and adjustment the catalyst composition.The effect of temperature on morphology and catalytic performance is investigated.900°C is the optimal temperature,and the synthesized material has the fantastic ORR/OER catalytic activity and ideal morphology.The onset potential and half potential of Fe Ni/N-C-900 is 0.88 V and 0.78 V,respectively.At 10 m A cm^-2,the OER potential of Fe Ni/N-C-900is 1.648 V.The good catalytic properties of Fe Ni/N-C-900 are derived from the Fe Ni alloy nanoparticles.3.In order to boost the utilization efficiency of catalytic active sites,the Fe and Ni dual-metal atomically dispersed catalyst（Fe/Ni（1:3）-NG）is synthesized through simple hydrothermal and pyrolysis steps.Here,graphene oxide is chosen as carbon substrate to anchor metal ions(Fe³⁺,Ni²⁺)by abundant oxygen-containing functional groups.Carbon nitride is served as nitrogen source.The contributions of different metal ions to ORR and OER are investigated.The electrochemical measurement results show the good ORR performance of nitrogen doped carbon materials.While adding trace Fe³⁺,the ORR activity of catalyst is improved,but the OER performance does not change.Adding trace Ni²⁺is beneficial to OER,but it is not good for ORR.The ORR and OER performance of Fe/Ni（1:3）-NG are greatly improved when trace amount of Fe³⁺and Ni²⁺added at the same time.The excellent catalytic performance of Fe/Ni（1:3）-NG is attributed to the synergy effect between Fe and Ni.The Fe/Ni（1:3）-NG based zinc battery demonstrated the outstanding power density(164.1 m W cm^-2),large specific capacity(824.3 m Ah·g^-1)and wonderful cycling stability（120 h）.