Study On Deposition Mechanism Of Ni/TiO₂ Composite Coating And Its Preparation From Deep Eutectic Solvent

Composite electrodeposition can effectively control metal materials to achieve nano-scale growth,and has been applied in the fields of supported structural materials,biosensing and catalysis.Because the composite electrodeposition process involves a complex solid-liquid two-phase interface,the deposition process of metal ions and inert particles is difficult to be directly observed,so most of the research on composite electrodeposition focuses on the performance of the coating.The study of the co-deposition behavior of inert particles and metal ions in the composite electrodeposition process is of great significance for controlling the growth of metal nanoparticles and guiding the preparation of functional coatings.Therefore,in this paper,the influence mechanism of the pre-adsorption of inert particles on the metal ion deposition in the initial stage of composite electrodeposition is studied,and a green Ni/TiO₂composite coating with higher hardness and stronger corrosion resistance is prepared in deep eutectic solvent.The nucleation and growth processes of nickel ions on the substrate surface at different potentials are studied.A set of multi-channel time-sharing common electrodeposition device is designed and developed,which can obtain the deposition samples at multiple times in one time,avoiding the electrodeposition condition deviation caused by multiple experiments and improve the experimental efficiency.The deposition of nickel ions at different times is observed by scanning electron microscopy.Combined with electrochemical methods such as chronoamperometry,the effects of different potentials on the nucleation and growth mode of nickel ions are studied,and the model of the effect of potential on the nucleation of nickel ions is established.The effect of pre-adsorption TiO₂ particles at the initial stage of composite electrodeposition on nickel ion electrodeposition is studied.Abnormal nucleation and rapid growth of nickel ions induced by pre-adsorbed TiO₂ particles were observed for the first time.A step-by-step electrodeposition method is proposed to separate the effect of pre-adsorbed TiO₂particles on nickel deposition from the composite electrodeposition.Combined with cyclic voltammetry curve and electrochemical impedance spectroscopy,the effect of pre-adsorbed TiO₂ particles on nickel ion deposition was revealed,and the physical model of pre-adsorbed inert particles affecting metal ion deposition is established.The effects of nickel sulfate as the main salt,boric acid and water on the preparation of Ni/TiO₂ composite coating in choline chloride-ethylene glycol eutectic solvent are studied.The solvent decomposition products such as light green nickel hydroxide by-products and trimethylamine doped in the coating during electrodeposition are analyzed by EDS and XRD.The mechanism of boric acid inhibiting the formation of deposition by-products and solvent decomposition was studied.The cyclic voltammetry curves reveal that water can change the complexation form of Ni²⁺in deep eutectic solvents and accelerate the reduction rate of nickel ions.In addition,the microhardness tester and electrochemical impedance spectroscopy analysis show that the Ni/TiO₂ composite coating prepared in deep eutectic solvent has higher hardness and stronger corrosion resistance than the Ni/TiO₂ composite coating prepared in aqueous solution.