Design Of Bifunction Ni-based Catalysts And Its Application In Zinc-air Batteries

With the rapid development of the modern industry and society,consequent problems in energy and environment are arising.More and more attentions are being paid on the development of green and sustainable energy sources.Currently,commercial lithium-ion batteries are faced with a series of problems,such as lithium is expensive and scarcity,electrolyte is toxic and flammable,and poor energy density.Therefore,it is urgent to develop energy storage devices with properties of high capacity,long cycle life,safety and environmental benignity to replace lithium-ion batteries.Zn-air batteries（ZABs）with unique advantages such as drastically high energy density,low-cost,operational safety and environmental benignity,have triggered great research enthusiasm.Oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）are the core reactions of air-electrode of ZAB,which determine the electrochemical performance of ZAB,such as energy conversion efficiency,specific capacity and stability.However,the sluggish kinetics and high overpotentials of ORR and OER processes have greatly limited the commercial application of ZABs.Therefore,great efforts are requested to explore low-cost,highly active and stable ORR and OER bifunctional electrocatalysis.Transition metals are abundant in the earth’s crust,the bifunctional activity is more easily realized by the combination of multiple transition metals,and the synergy effect of the bimetals can effectively improve the catalytic activity by modulating electronic structure of the metal sites.In this paper,the effective regulations on the electronic structure and nanostructure are applied in the catalyst design to obtain active materials with high intrinsic bifunctional ORR/OER activity.The liquid and flexible ZABs based on the designed electrocatalysts were exhibited excellent electrochemical performance,conclusions are as follows:1.By anchoring Ni Fe alloy nanoparticles on nitrogen-doped carbon nanotubes（N-CNT）,an efficient and stable bifunctional electrocatalyst Ni Fe/N-CNT was synthesized,which demonstrated favourable catalytic activity in OER and ORR.Density functional theory,in-situ Raman and oxygen adsorption analyses have demonstrated that the embedded Ni Fe structure can strengthen the adsorption capabilities of OH^-and oxygen which are considered as a crucial step for OER and ORR in alkaline media,respectively.The liquid ZAB based on Ni Fe/N-NCT exhibits excellent power density,specific capacity and cyclic stability.The corresponding flexible ZAB demonstrates excellent electrochemical perfromances as well as mechanical strength.2.Ni Co₂O₄/MXene bifunctional electrocatalyst was facilely fabricated via in-situ anchoring ultra-fine Ni Co₂O₄ nanoparticles on few-layer MXene framework.Due to the synergistic effect between MXene and Ni Co₂O₄ demonstrated by Near edge X-ray absorption fine structure spectroscopy and X-ray photoelectron spectroscopy,the electrocatalyst exhibits excellent ORR/OER bifunctional activities.The liquid and flexible ZABs based on Ni Co₂O₄/MXene bifunctional electrocatalyst both exhibits excellent electrochemical perfromances.