Preparation And Electrochemical Properties Of Nickel-based Layered Double Metal Hydroxide Composites

The ever-increasing demand for clean energy drives the rapid development of energy conversion and storage devices,for which the development of new electrode materials is crucial.Nickel-based layered double hydroxides（LDHs）have attracted much attention of researchers due to their large specific surface area and tunable layered structure.However,limited by the poor structural stability and low charge transfer ability,nickel-based LDH still has a lot of space for improvement from the requirements of high-performance electrode materials.In this thesis,aiming at the development of high-efficiency bifunctional electrode materials,nickel-based LDH was modified by anion intercalation and metal cation regulation,and an integrated strategy was adopted to construct LDH composite electrodes in situ.The evolution mechanism for microstructure and morphology of the prepared active materials were explored by combining phase and micromorphological characterization methods.The energy conversion and storage mechanism were revealed by comprehensively corresponding electrochemical test methods.The specific work is described as follows:（1）The samples were synthesized by a facile hydrothermal method.The sodium dodecyl sulfate（SDS）was used as the intercalating agent for regulating the interlayer structure of LDH.The results reveal that the redistribution of charge-compensating ions between the LDH layers due to the introduction of SDS may be the main reason for the transformation of nanoflakes to nanowire/nanosheet hierarchical structure.The amount of SDS intercalating agent does not show a positive correlation with the electrochemical performance of the synthesized LDH.The CSL-2 exhibits the high specific capacity of 509.2 C g^-1at 1 A g^-1.Further analysis indicates that its high specific capacity performance mainly benefits from the electrochemical energy storage behavior dominated by the diffusion-controlled process.As-prepared supercapacitor exhibits a specific capacity of 73.5 C g^-1at a current density of 1 A g^-1,demonstrating its impressive charge storage capability.The results of electrocatalytic hydrogen evolution tests performed on CSL-2 suggest that a lower overpotential of181 m V is required to obtain 10 m A cm^-2in 1 M KOH electrolyte.Furthermore,it was tested for hydrogen evolution for 10 h at this overpotential,and the performance has 98.1%retention with almost no decay.（2）As derivative,Co₂NiO₄/NF was controllably synthesized by employing NiCo-LDH/NF as a precursor.Next,the integrated NiV-LDH@Co₂NiO₄/NF electrode was synthesized by secondary hydrothermal deposition of NiV-LDH on Co₂NiO₄/NF.Studies have shown that vanadium and nickel-based LDH have a highly matched crystal structure,so it is easy to precipitated into the layers of LDHs hydrothermally.The introduction of vanadium changes the surface energy during crystal growth,which leads to changes in the morphology and size of the nanosheets,and finally evolves into nano-coral arrays.Furthermore,the doping of vanadium induces the formation of additional electrocatalytically active sites on the electrode surface,which greatly promotes the improvement of electrochemical performance.In the energy storage performance test,NiV-LDH@Co₂NiO₄/NF has a high specific capacity of1381.8 C g^-1at 1 A g^-1.There are 79.8%of capacity retention after 5000 cycles GCD tests at the increased current density of 5 A g^-1.The as-prepared quasi-solid-state hybrid supercapacitor exhibits the power density of 878.6 W kg^-1at 68.7 W h kg^-1,while the power density increases to 7097.1 W kg^-1,it can output the energy density of 29.6 W h kg^-1.Connecting two same supercapacitors in series can continuously provide energy for an LED lamp with an operating voltage of 2.2 V,fully demonstrating its great potential for practical applications in the field of electrochemical energy storage.The electrocatalytic hydrogen evolution performance results show that it only needs the overpotential of 86 m V to reach the current density of 10 m A cm^-2,while the overpotential reaches 350 m V,the current density on the electrode has increased tenfold.NiV-LDH@Co₂NiO₄/NF exhibits excellent performance in the fields of supercapacitors and electrocatalytic water splitting for hydrogen evolution,which also provides an effective reference for the design and synthesis of integrated bifunctional LDH electrode materials in the future.