Synthesis Of Nanomaterials Derived From Metal-organic Frames And Study On Performance Of Mixed Zinc Base Supercapacitor

Due to the uneven distribution in time and district of green and renewable energy（solar energy,tidal energy and wind energy）,the electric energy produced by these renewable energy can not directly fed into the grid,which may increase the percussive load of power network.Therefore,the development of high-performance electric energy storage devices is necessary to,cut peaks and fill valleys of the grid,and reduce the phenomena of light abandonment and wind abandonment.Supercapacitors have drawn wide attention because of their long cycle life,high power density and high safety,and are considered as one of the promising energy storage devices.It is well known that the performance of supercapacitor is determined by their electrode materials.To achieve high energy density at high power density,the electrode materials should possess ultra-high specific surface area for more active center and rich pore structure for fast mass transfer and reliving volume effect during rapid charge and discharge process.In addition,according to formula of energy density,the output voltage also plays an important impact on the energy density of supercapacitor devices.Therefore,the design and assembly of high-performance hybrid supercapacitor devices is one of the hot research directions in this field.In this dissertation,using the metal-organic framework as the precursor,the hollow Ni₃Se₄@Co₃Se₄ double-shell microspheres,the basic cobalt phosphate/nickel phosphate hierarchical core-shell microspheres and hollow nickel boride microspheres are constructed by controlled liquid phase etching process,which successfully inherit the high specific surface area and rich pore structure of their parents.The unique hollow or double-shell structure and abundant macroporous/mesoporous-microporous mass transfer channels can realize rapid mass transfer and alleviate the volume effect during charge and discharge,significantly enhancing the ratio and cycle stability of as-prepared electrode materials.In addition,the prepared electrode material is further assembled into a hybrid supercapacitor system with AC or zinc anode,which significantly improves the output voltage of capacitors.Especially,the hybrid zinc-based supercapacitor devices deliver a stable output voltage platform of above 1.5 V,which can meet the requirements of most civil devices.The research content can be divided into three systems,as follows:1.Construction of Ni₃Se₄@Co₃Se₄ double-shell microspheres and their supercapacitor performance:A novel double-shell microsphere with Ni₃Se₄ as the outer layer and Co₃Se₄ as the inner layer（Ni₃Se₄@Co₃Se₄）has been constructed by LDH coating and then Se^2-etching strategy.This strategy presents certain universality and can be extended to Ni and Mn systems.To construct Ni₃Se₄@Ni Se and Ni₃Se₄@Mn Se double-shell microsphere.During Se^2-etching process,the organic ligands in the core and OH^-in the shell will be gradually replaced by Se^2-to obtain the target selenides.The released free ligands and OH^-will migrate out of the material,and the migration of ions will form rich ion diffusion channels,for fast electrolyte mass transfer.Therefore,the specific capacitance of the optimized Ni₃Se₄@Co₃Se₄-1:3 sample can reach 1120.4 F g^-1 at the current density of 1 A g^-1,and the Ni₃Se₄@Co₃Se₄-1:3 present excellent rate performance of maintaining 92.1%of the initial capacity when the current density is increased by 10 times.Then the Ni₃Se₄@Co₃Se₄-1:3//AC asymmetric supercapacitors and Ni₃Se₄@Co₃Se₄-1:3//r Go-Zn zinc base hybrid supercapacitors are assembled by taking Ni₃Se₄@Co₃Se₄-1:3 as positive electrode and AC and r GO functional zinc plates as negative electrode respectively.The electrochemical test results show that the energy density of Ni₃Se₄@Co₃Se₄-1:3//r GO-Zn can reach about 6 times than Ni₃Se₄@Co₃Se₄-1:3//AC due to the increased output voltage.The Ni₃Se₄@Co₃Se₄-1:3//r GO-Zn display a high energy density of 271.18 Wh kg^-1 at the power density of 1.67k W kg^-1.The Zn negative electrode can dramatically improve the energy density of supercapacitors,which provides a feasible path for the research and development of dual-high energy storage devices with both high energy density and high power density.2.Construction of hierarchical basic Co/Ni phosphate core-shell microspheres for mixed zinc-based supercapacitors application:By adjusting the ratio of OH^-and PO₄^3-ions of etching solution,a series of basic core-shell microspheres（BCNP）with"tree vein"hierarchical pore structure were constructed.In the process of etching,BTC^3-with large molecular size is in situ replaced by OH^-and PO₄^3-with small molecular size,resulting in local size shrinkage effect to form lots of mesoporous pore structure.At the same time,the competitive coordination of OH^-and PO₄^3-ions will produce disordered microporous channels,which are connected with mesoporous pore channels to form tree-vein pore structure.The unique tree-vein pore structure can effectively increase accessible active center and ensures rapid electrolyte supply to the active center.Thus,the BCNP finally achieves a high specific capacitance of 1601.4 F g^-1 at a current density of 1 A g^-1,as well as an excellent ratio performance that maintains an initial capacitance of 82.2%with the current density increased from 1 to 10 A g^-1.In addition,the assembled BCNP//r GO-Zn hybrid supercapacitor devices can achieve an energy density of376.5Wh kg^-1 at a power density of 1.658 k W kg^-1,which is much higher than most reported supercapacitor devices.Moreover,the BCNP//r GO-Zn device presents a charging and discharging platform above 1.5 V,and can power the thermometer for more than 3 hours when the charging time is about 1 minute,which shows outstanding application prospect.3.Construction of hollow nickel boride microspheres for Zinc-based hybrid supercapacitors application:In this study,we develop a method for preparing bimetallic boride hollow nanospheres.Firstly,uniform Co/Ni MOFs bimetallic microspheres with different Co/Ni ratios are prepared by hydrothermal method,and then Co-doped Ni₂B hollow microspheres（CNB）with low crystallinity are obtained by reduction of Na BH₄.The low crystalline phase of CNB produce a large number of defects in the material,which is benefit to increase the active sites for electrochemical reactions.Meanwhile,the unique hollow structure can shorten the electron transfer/ion diffusion path and expose more charge storage active centers for high specific capacity.Therefore,the optimized CNB hollow sphere show a high specific capacitance up to2173 F g^-1 and excellent cycle life.In addition,the asymmetric supercapacitor device composed with r GO-Zn shows an excellent energy density(454.72Wh kg^-1)at a power density of 0.46k W kg^-1,which display excellent application value.