Study On Supercapacitor And Electrocatalytic Water Splitting Properties Based On NiCo Bimetallic Compounds

With the rapid development of economy and society,the utilization of energy resources is becoming increasingly critical for human life and social development.However,the over-exploitation of traditional resources such as coal,oil and natural gas has caused serious environmental problems and energy crisis.Renewable energy conversion and storage technology is considered to be an effective and convenient strategy for energy production and one of the effective ways to solve energy problems.Nowadays,there has been a large number of renewable energy devices,including fuel cells,lithium-ion batteries,supercapacitors,metal air cells,solar cells,etc.Among them,electrocatalytic water decomposition and supercapacitors have the characteristics of high working efficiency,stable working voltage platform and strong mechanical stability,which have attracted extensive attention of scientific research personnel.As an electrode material,the design of different reactions requires combination of several factors to obtain good electrochemical performance.Some of these factors are common to all electrocatalysts or supercapacitors,such as high surface area,fast mass transfer rate,and high conductivity,others may be exclusive to specific applications,such as electronic structure,crystal phase,ion/mass adsorption/desorption capacity,and physical structure.Therefore,it is very important to find suitable electrode materials to accelerate the energy conversion efficiency of the supercapacitors and overall water decomposition reaction.Ni Co transition-metal-based materials are considered as alternative electrode materials for commercial noble-metal-based catalysts such as ruthenium and iridium due to their unique two-dimensional layered structure and easy regulation of electronic structure.However,because the nanoparticles are easy to agglomerate,there are some weaknesses in the conductivity and active site,which limit its further application in the field of electrode materials.Based on these factors,in order to improve the defects or deficiencies of Ni Co transition-metal-base materials,several convenient preparation routes are designed purposefully,and three kinds of Ni Co transition-metal-based electrode materials with unique properties were successfully synthesized,following by the morphology characterization and application performance testing.The specific contents of this paper are as follows:1.An Oxygen-rich vacancy nickel-cobalt layered-double-hydroxide（O_v-Ni Co-LDH）with excellent supercapacitive properties was prepared by electrodeposition and in situ oxidation on a nickel foam collector.The oxygen vacancy concentration of the ultrathin nanosheets was adjusted by H₂O₂ treatment.This unique structure achieves high electrolyte accessibility and greatly reduces the diffusion path of electrolyte ions.At 1 A·g^-1 current density,the specific capacitance of O_v-Ni Co-LDH reaches 1160 C·g^-1,which is higher than that of most similar supercapacitor electrode materials.In addition,when it is assembled into symmetrical supercapacitor devices as both positive and negative electrode materials,excellent energy density and power density(216.19Wh·kg^-1 at a power density of 1.75 k W·kg^-1)and high cycle stability（71.45%capacitance retention after 2000 cycles）are obtained2.The O_v-Ni Co-LDO HNTAs/NF,which are hollow nanotubes with rich oxygen vacancy,have been prepared on bare foam nickel by electrodeposition,solid vapor deposition and hydrothermal method.The structure of the hollow nanotube array and the consentration of oxygen vacancy were regulated by etching Zn O template and glycol reduction,respectively.This unique hollow structure is conducive to the rapid transport of electrolyte ions and provides abundant active specific surface area and active sites.The O_v-Ni Co-LDO HNTAs/NF electrode material showed excellent electrocatalytic water splitting performance.The overpotential were 149 and 30 m V at the current density of 10 m A·cm^-2towards OER and HER,respectively,which shows excellent cyclic stability.In addition,the water decomposition device provides ultra-low water splitting potential(1.56 V at 10 m A·cm^-2 current density)and high cyclic stability（no significant performance degradation after 24 hours of cycling）.3.Ti₃C₂ MXene was synthesized by two-stage hydrothermal method,and Se doping was used to prepare Ni Co Se@MXene nanocomposites with excellent performance of HER and supercapacitor.The conductivity of Ni Co Se@MXene nanocomposites has been improved by the combination of ultra-high conductivity Ti₃C₂MXene.In addition,the lamellar structure of Ni Co Se@MXene provides a higher specific surface area and active site,greatly enhancing its electrochemical activity.After optimization,Ni Co Se@MXene nanocomposite showed excellent electrocatalytic performance of HER,with a hydrogen evolution potential of 40 m V in alkaline electrolyte solution at a current density of 10 m A·cm^-2,low Tafel slope and high stability.In addition,Ni Co Se@MXene nanocomposites also exhibit excellent ultracapacitor performance when used as electrode material for supercapacitors.When the current density is 2 A·g^-1,the specific capacitance value is up to 2710 F·g^-1,and the capacitance retention rate remains 77.8%after 5000 cycles.