Benzoate Anion-intercalation Transition Metal Hydroxide Nanostructures: Synthesis And Capacitance Property

With the continuous consumption of fossil fuels and environmental pollution,it is imperative to develop clean alternative energy and advanced energy storage systems.As a new energy storage system,supercapacitors have received extensive attention from researchers due to their advantages of high power density,fast charging/discharging,and outstanding cycle stability and safety.However,its lower energy density limits its development.Transition metal hydroxide has become one of the current research hotspots due to its high capacitance and environmental friendliness.Due to problems such as slow reaction kinetics and inevitable volume changes at high charge/discharge rates,most layered hydroxides exhibit poor rate performance and electrochemical stability.The electrode material with a multi-dimensional hierarchical structure can significantly improve its electrochemical performance.For transition metal layered hydroxides,increasing the distance between layers is a very good way to improve electrochemical performance.According to the exchangeability of anions between layers of the layered metal hydroxide,the distance between layers can be adjusted by intercalating anions of different lengths.However,the correlation between the rate performance of ion diffusion and the distance between layers is unclear.In this work,a series of benzoate anion intercalated layered hydroxide nanomaterials were prepared in order to expand the interlayer spacing under the nanoscale structure.At the same time,the capacitance performance of the prepared materials was also tested.Scanning electron microscope(SEM),transmission electron microscope(TEM),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),specific surface area analysis(BET)and fourier transform infrared spectroscopy(FT-IR)are used to characterize the crystal structure,composition,and microscopic morphology of the materials.Cyclic voltammetry(CV),galvanostatic charge–discharge(GCD),cycle stability and alternating current impedance test(EIS)are used to characterize the electrochemical properties of the material.The research content mainly includes the following two aspects:i)B-M-LHSs(M=Co,Ni,and Co Ni)intercalated with benzoate ion were synthesized by a one-step co-precipitation method.The three synthesized materials are all one-dimensional nanoribbon-like microscopic morphologies.B-Co Ni-LHSs exhibits better electrochemical performance than the other two single metal samples in the three-electrode system,which may be the synergistic effect of cobalt and nickel metals.The B-Co Ni-LHSs electrode can reach a high specific capacity of 570 C g^–1(1267 F g^–1)at 1 A g^–1,and it can still maintain 81.09%of the original capacity after8000 GCD cycles.The hybrid supercapacitor device(denoted as B-M-LHSs//AC)assembled using B-Co Ni-LHSs and commercial activated carbon(AC)as the positive electrode material and the negative electrode material can reach a voltage window of0-1.6V by finding the potential through CV and GCD test.Compared with the other two devices,the B-Co Ni-LHSs//AC device exhibits a higher energy density(31.7 Wh kg^–1 at 780 W kg^–1).ii)First of all,ZIF-L-Co was synthesized using 2-methylimidazole and cobalt nitrate hexahydrate.Then,Zn_xNi_1-xCo-LDH-NO₃^–(x=0,0.25,0.5,0.75,and 1)with different Zn/Ni ratios were prepared using water-assisted co-precipitation and ion etching processes.Finally,the prepared Zn_0.25Ni_0.75Co-LDH-NO₃^–is subjected to an ion exchange process to obtain benzoate ion(BA^–)intercalated Zn_0.25Ni_0.75Co-LDH-BA^–and acetate ion(AA^–)intercalated Zn_0.25Ni_0.75Co-LDH-AA^–.We found that Zn_0.25Ni_0.75Co-LDH-NO₃^–shows better electrochemical performance among the five materials prepared with different Zn/Ni ratios in the three-electrode system test.In the prepared Zn_0.25Ni_0.75Co-LDH intercalated with BA^–,AA^–,and NO₃^–,Zn_0.25Ni_0.75Co-LDH-BA^–showed a higher specific capacity(378 m Ah g^–1 at 1 A g^–1)and longer-lasting cycle stability(91.2%capacity retention after 10,000 GCD cycles).A hybrid supercapacitor(denoted as Zn_0.25Ni_0.75Co-LDH-BA^–//AC)assembled using Zn_0.25Ni_0.75Co-LDH-BA^–as the positive electrode and AC as the negative electrode.It can reach a voltage window of 0-1.6 V,and can simultaneously reach an energy density of 52.5 Wh kg^–1 and a power density of 800 W kg^–1.