Design Of Co-based Nanomaterials And Their Applications In Electrocatalysis And Energy Storage

Energy supply is a key issue for the sustainable development of modern society.Especially when confronted with continuing population growth,increasing depletion of fossil fuels,and worsening effects of climate change,it is essential to develop new clean and sustainable energy sources.In the pursuit of energy security,energy conversion and storage technologies are essential to accelerate large-scale exploitation of these sources.The electrochemical rechargeable batteries(Li-ion battery?LIBs?and electrocatalysis processes?e.g.oxygen evolution reaction?OER?,hydrogen evolution reaction?HER??have been more and more explored.Transition metal compounds have received ever-growing research interests as potential electrode materials for energy storage and conversion due to its tunable stoichiometric compositions,unique crystal structures,and rich redox sites,as well as relatively higher electrical conductivity compared with their transition metal oxide counterparts.However,the challenges of the low special surface area,inferior reactivity,and low electron/ion transfer rate,remain for the practical applications of transition metal compounds in energy devices.Hence,in this article,the reactivity and electron/ion migration rate of materials are improved by designing materials with special structure and compounding them with conductive materials to form heterostructures,so as to enhance their electrochemical properties.The primary contents are as follows:1.Preparation and electrochemical properties of CoS/NC@MoS₂ hollow spheres.Firstly,ZIF-67 hollow spheres were synthesized at room temperature,then in-situ pyrolysis and sulfurization process to obtain CoS/NC hollow spheres.Finally,CoS/NC@MoS₂ hollow spheres were prepared by hydrothermal method.The material exhibits outstanding electrochemical performance when used as HER catalysts and lithium ion batteries anode material:In acidic medium,the overpotential is only 77 mV at 10 mA cm^-22 current density,and a Tafel slope of 67 mV dec^-1,with remarkable stability over 20hours.When the current density increased to 1 A g^-1,a reversible specific capacity of about 802.4 mAh g^-1 still could be achieved over 400 cycles.The excellent electrochemical performance is mainly due to the well-coupled interface between MoS₂and CoS/NC makes full use of the inherent properties of individual MoS₂ and CoS/NC,producing strong electron transport and more active sites between the two phases.2.CoB/FeB composites with good crystallinity for electrochemical water decomposition.The amorphous CoB/FeB composites were obtained by a simple chemical reduction method,and then it was uniformly mixed with sodium borohydride and calcined in a H₂/Ar mixture to obtain a CoB/FeB composite with good crystallinity.The electrochemical properties of the composite materials are different with the content of iron and cobalt.When the content ratio of Fe to Co is close to 1:1,the performance of the composite is the best.Taking Co-Fe-B as an example,when the current density is 10 mA cm^-2,the overpotentials are 109 mV?HER?and 280 mV?OER?,respectively,and the corresponding Tafel slopes are 86.7 mV dec^-1?HER?and 65.4 mV dec^-1?OER?.3.Preparation and lithium storage properties of flower-like Co₃S₄/C nanosheets.Flower-like Co₃S₄/C nanosheets were prepared by one-pot solvothermal and pyrolysis methods.In this method,the flower-like structure of nanosheets was obtained by controlling the type of sulfur source,adding the volume of concentrated ammonia,reaction time and temperature.The final pyrolysis is on the one hand to carbonize the ligand and on the other hand to increase the crystallinity of the material.This unique structure of the material shows good cycle performance.When the current density increases to 400 mA g^-1,the capacity is still stable at 1200.7 mAh g^-1 after 300 cycles.Experiments show that the electrochemical properties of carbon-containing materials have been significantly improved,which put down to the existence of carbon not only increases the conductivity of materials,but also improves the stability of materials.