Construction Of High Efficiency Nickel-based Electrocatalysts For Oxygen And Their Electrochemical Reactions Application In Zinc-air Battery

The development and utilization of renewable energy sources have attracted much attention with the problem of energy shortage and environmental pollution getting worse and worse.In order to achieve the social goals of green,economic,and sustainable development,which is “We want clear water,green mountains and gold,silver as well”,scientific researchers are committed to developing alternative new energy storage and conversion technologies.Metal-air batteries and fuel cells are considered to be the most hopeful and promising sustainable energy sources.Among them,safe and environmentally friendly zinc-air batteries(ZABs)have brought about widespread attention.On the one hand,ZABs show a quite high energy density;On the other hand,zinc has a high theoretical specific energy and nominal voltage;At the same time,zinc has abundant reserves which is really cheap.However,the slow ORR(oxygen reduction reaction)and OER(oxygen evolution reaction)have seriously hindered ZABs? development and practical application.The key is to research and develop the low-cost and high-performance bifunctional electrocatalysts.The current study is still in its infancy and faces many challenges.In this paper,we select nickel-based materials with high catalytic activity and construct a structure with a large specific surface area to promote the bifunctional performance of the catalyst together.The main research contents are as follows:First,a simple strategy was designed to synthesize a free-standing bifunctional oxygen electrocatalyst,Ni S nanowire supported on foam nickel,in situ by hydrothermal method(denoted as Ni S/NF).The free-standing structure does not have any binder,what greatly increases3 the conductivity and stability of the catalyst.At the same time,the electrocatalytic synergistic effect between nickel foam and nickel sulfide nanowires promoted electron transfer,improved electrical conductivity,changed the surface electronic structure,and significantly improved the OER and ORR electrocatalytic activity of a single component as well(E1/2=0.72 V,?=280 m V).The liquid ZABs with Ni S/NF as catalyst has a higher power density(226 mW cm-2)and superior stable cycle performance(380 h),even comparable to commercial precious metal catalysts(Pt/C).This work provided a prospective idea and strategy for rechargeable ZABs.Subsequently,Fe/N co-doped carbon nanofibers(Fe-N-CNFs)were prepared by electrospinning technology.And ultra-thin Ni Fe LDH(Layered Double Hydroxide)nanosheets were loaded on Fe-N-CNFs to solve the problem of single functionality.After that,we made a ZABs with Ni Fe LDH@Fe-N-CNFs as the cathode showing outstanding catalytic activity and stability,benefiting from the Fe-N-C active sites in the Fe/N co-doped carbon matrix,the uniformly loaded Ni Fe LDH and the large specific surface area of the cross-linked network nanostructure.The battery can discharge steadily at 1.2 V for 35 hours with constant current and can achieve a specific capacity of 695.2 m Ah g-1.It still can stably cycle for 75 hours at a high current density(20 mA cm-2).