Preparation And Supercapacitor Properties Of Nickel-based Selenides

With the increasing energy crisis and environmental problems,the demand for clean energy is increasing.Research and development of efficient energy conversion and storage devices has become a key issue.As a new type of green electrochemical energy storage device,supercapacitors stand out among many energy storage devices because of their considerable energy storage capacity,high output power density,excellent cycle life,low energy consumption and environmental friendliness.As multifunctional materials with high conductivity and high electrochemical activity,transition metal selenide have been successfully applied in many fields.However,the current reports on transition metal selenides as electrode materials for supercapacitors are very limited,and the existing work is still limited to the synthesis and research of metal selenides with simple structure and single composition.The problems of low utilization rate of materials and agglomeration of particles are often unavoidable,resulting in unsatisfactory electrochemical performance of these selenides.Therefore,it is of great research significance to prepare electrode materials with high specific capacitance and excellent rate performance through reasonable material composition and structural design to give full play to the high conductivity advantage of transition metal selenide materials and further improve their charge storage capacity.Based on the above considerations,the main research contents of this paper are:A binary metal?Ni,Co?Se₂ nanowire array was directly constructed on a flexible carbon cloth?CC?substrate by a simple two-step method.After the heat treatment selenization,a uniform and regular nanowire array structure for the Ni-Co-based precursor was highly retained.The effect of two metal ions on the morphology and electrochemical properties of the material was revealed by comparing the ratios of different Ni/Co.The binary metal?Ni,Co?Se2 exhibits higher electrochemical activity than the mono-metal selenide electrode,where NCS/CC-1 achieves 1227.2 F g^-1 at a current density of 1 A g^-1(with a specific capacitance of 1.84 F cm^-2),the assembled NCS/CC-1//AC has an energy density of 38.5 Wh kg^-1 at a power density of 800 W kg^-1.A hierarchical NiSe@Co₂?CO₃??OH?₂ heterogeneous nanowire array was fabricated on nickel foam?NF?using a simple two-step soft chemical route.The NiSe nanowires with excellent conductivity were built in situ on the NF surface,and serve as a bridge between high-speed electron transport between electroactive materials and the current collector while exerting their capacitive properties.The Co2?CO3??OH?2 nanowires grew transversely on NiSe to form a one-dimensional heterostructure,which provides more electrochemical active sites.As a result,the electrode achieves an excellent areal specific capacitance of 9.56 F cm^-2(at a current density of 4 mA cm^-2).The energy density of NiSe@Co₂?CO₃??OH?₂//AC hybrid supercapacitor reaches 0.89 mWh cm^-2(at a power density of 3.2 mW cm^-2).A bimetallic hollow?Ni,Co?0.85Se nanocage was prepared by a two-step etching and hydrothermal method using the Metal-Organic framework compound ZIF-67 as a template.The Ni element is introduced into the material by etching of Ni?NO3?2,and the precursor nanocage is transformed into a yolk-shell structure in which the ZIF-67 core is wrapped by the nanosheet stacking shell.After hydrothermal selenization,the core was completely removed and the nanocage shell is retained.The superior electrochemical properties of as-prepared material due to its high specific surface area structure with porous surface and hollow interior.?Ni,Co?_0.85Se nanocage exhibits a specific capacitance of 1062.7 F g-1 at a current density of 2 A g-1,and the assembled?Ni,Co?_0.85Se//AC has a power density of up to4 kW kg^-1,the energy density can still reach 19.2 Wh kg^-1.