Study On The Preparation And Electrochemical Application Of Electrode Based On Metal Micro-nano Structure Skeleton

Excessive exploitation and use of fossil fuels have seriously endangered the survival and health of human beings.The transformation and storage of clean energy have been paid more and more attention.A large part of the clean instantaneous energy such as solar,tidal and wind power is not well utilized,resulting in considerable energy waste.Therefore,it is necessary to carry out large-scale storage and conversion of electric energy,such as storing electric energy into energy storage devices or converting electric energy into hydrogen energy through electrocatalysis.As a kind of energy storage device with high power density,the capacitor can make up for battery shortcoming in energy storage.It can charge and discharge rapidly and has good long-term cycle stability.Researchers have combined the benefits of batteries and capacitors into a new type of energy storage device called pseudocapacitor.In order to ensure that the supercapacitor has both a fast energy storage rate and a large charge storage capacity,it is necessary to increase the electrode material load and the redox reaction rate.However,the two are negatively correlated to a large extent,and a large amount of bulk active substances actually reduce the redox rate.In recent years,researchers have improved the loading capacity and reactivity of active materials by optimizing electrodes'structural design,thus speeding up the energy storage process.We designed a series of surface structured nickel thin films loaded with various forms of nanomaterials as electrochemical electrodes for energy storage and conversion.A large number of three-dimensional micro-and nanostructure arrays are arranged on the structured nickel thin film,resulting in the electrode substrate with a large surface area.We have developed a new method to fabricate micro-and nanostructured metal electrodes by combining photolithography,reactive ion etching,nanoimprint and electroplating.The growth of porous transition metal sulfide nanomaterials on this three-dimensional substrate can further increase the transfer rate of electron and ion during redox.We chose Ni Co₂S₄,a binary metal sulfide,as the active electrode material,which has excellent electrochemical activity and electronic conductivity.More importantly,Ni Co₂S₄ can be synthesized into a variety of nanomaterials with large specific surface areas,which can provide much more electrochemically active sites.In this paper,the energy storage and electrocatalysis of the electrode composed of structured nickel film and Ni Co₂S₄ have been studied and the specific contents are as follows:The preparation and performance study of electrochemical energy storage of Ni Co₂S₄/NC array electrode.Vertically aligned and ordered arrays of Ni Co₂S₄nanoflake covered slender nickel columns(NCs)are achieved by thermal nanoimprint lithography(T-NIL),electroplating in combination with hydrothermal growth.The composite structure consists of two kinds of straight ion-movement channels.One is the large channel formed by the gap between the Ni micron column arrays as the downward transport of ions,and the other is the small channel provided by the gap between the two-dimensional Ni Co₂S₄ lamellar nanoflakes for the internal transport of ions.The vertical standing?5 nm ultrathin Ni Co₂S₄ nanoflakes build a porous covering with straight ion channels without the“dead volume”,leading to thickness-independent capacity.Benefiting from the architecture acting as a“superhighway”for ultrafast ion/electron transport and providing large surface area,high electrical conductivity and abundant availability of electrochemically active sites,such Ni Co₂S₄@NC-array electrode achieves a specific capacity reaching up to 486.9 m Ah g^-1.The electrode even can work with a high specific capacity of 150 m Ah g^-1 at a very high current density of100 A g^-1.In particular,due to the advanced structure features,the electrode exhibits excellent flexibility with an unexpected improvement of capacity under large bending,and excellent cycling stability with a noticeable resistance decrease after cycles.An asymmetric pseudocapacitor applying the Ni Co₂S₄@NC-array as a positive electrode achieves an energy density of 66.5 Wh kg^-1 at a power density of 400 W kg^-1,much superior over most reported values for asymmetric devices with Ni Co₂S₄ electrodes.This work provides a scalable and simple approach toward achieving thickness independent electrodes with ultrafast ion/electron transport for energy storage.Preparation and study on the electrochemical properties of coral-like structure nanomaterials.In order to investigate the influence of nanoscale metal skeleton on the electrochemical energy storage performance of the electrode.We report hierarchically porous,high surface area electrodes consisting of a 3D current collector of nickel nano-branches(NNB)covered with Ni-Co-S nanoparticles with sulfide vacancies.Much different from previously reported collectors,such as nickel foams with micron-size ligaments and disorderly distributed ultra-large pores,the NNB are rooted in a thin slice,and each nano-branch interconnect to each other,forming multi-dendritic nanostructure arrays.After the growth of Ni-Co-S nanocrystals,the whole electrode has a coralloid composite nanostructure.The nickel nanoarray provides a fast path for electron transport and facilitates rapid ion diffusion near the surface of active Ni-Co-S.The Ni-Co-S@NNB electrode exhibits extremely high rate performance with 91%capacity retention from 1 to 20 A g^-1,and even still remains 83.6%capacity at 40 A g^-1,much superior to the reported Ni Co₂S₄-based electrodes.This is attributed to the unique nano-architecture providing increased ion availability of electrochemically active sites and high conductivity for fast electron transport.Especially the electrode achieves remarkable long-term cycle stability with more than 100%initial capacity value after5,000 cycles at 5 A g^-1,and exhibits excellent cycle reversibility even at 20 A g^-1.This should be attributed to the sulfide vacancies in Ni-Co-S nano-branches,and the NNB provides better accommodation of the mechanical and structural strain associated with fast electrochemical reactions.An asymmetric pseudocapacitor applying such electrode achieves a high energy density of 99.9 W h kg^-1 and exhibit superior cycling stability at a high current density of 20 A g^-1.This work has a large spatial extension and provides a new path for developing highly redox-active complex nanostructured electrodes.Preparation of metal-based micro-nano composites and their applications in water electrolysis.In order to exert the catalytic ability of electrocatalysts,it is necessary to regulate the electronic structure and micro morphology of materials.For most transition metal compounds,the active sites are mainly located at the edge of the structure,while the tightly packed inner region prevents the formation of active catalytic sites.Therefore,creating more edge regions by designing nanostructures with large active surface area is expected to improve the electrocatalytic performance.We have designed a three-dimensional electrocatalytic electrode with a large edge region.The one-dimensional Ni Co₂S₄ nanowire arrays are arranged on the nickel micron column arrays,forming a multilevel micro-nano composite electrode structure.By increasing the contact area between the electrode and the solution,the system resistance and overpotential caused by electrode polarization were reduced,and the rate of electrochemical water splitting was enhanced.We compared the catalytic performance of Ni Co₂S₄ nanosheet with that of nanowires,and the Ni Co₂S₄ nanowires with the larger specific surface area had a better electrocatalytic performance.The current density generated by the hydrolysis reaction is as high as 108.2 m A cm^-2 at the overpotential of570 m V.The high oxidation peak indicates that this electrode is also an excellent electrochemical energy storage electrode.The electrochemical impedance spectroscopy(EIS)test shows that the charge transfer resistance(R_ct)of the electrode is very small,which indicates that the Ni Co₂S₄-NW@NC electrode has excellent interfacial charge transfer ability,which confirms that the electrode has excellent electrocatalytic activity and excellent electrocatalytic activity.In addition,we also conducted a long-term stability test for 20 hours,and after 20 hours of operation,the electrode still showed excellent electrocatalytic activity.