Preparation Of Co-P Functional Thin Film Materials By Additive-assisted Deep Eutectic Solvent Electrodepositio

Co-P has good qualities such as magnetic properties,mechanical properties,wear resistance,and strong corrosion resistance,making it a perfect alternative for hard chromium plating.At the same time,the Co-P thin film material has good electrocatalytic hydrogen evolution performance and is an ideal cheap catalytic electrode material.Electrodeposition technology is an effective method for preparing Co-P thin film electrodes that can be carried out in aqueous systems with a wide p H range;however,this process is accompanied by hydrogen evolution side reactions that seriously affect the quality and performance of thin film coatings.Compared with the traditional aqueous solution system,the deep eutectic solvent is a new type of electrolyte with a stable structure,controllable properties,and non-interference from the side reaction of hydrogen evolution.It can be used for the controllable preparation of functional Co-P thin film material materials by electrodeposition.In addition,the electrodeposition process of Co-P can be regulated by the introduction of appropriate additives in the deposition system,and then Co-P coatings with specific micro-morphology,crystal structure,element and species composition,good corrosion resistance,and catalytic performance can be obtained.In this paper,the influence of additives in choline chloride-ethylene glycol deep eutectic solvent（Ethaline）on the electrodeposition of Co-P thin film materials is systematically explored.The main research contents and results are as follows:（1）The effects of additives（saccharin（SA）and 1,4-butynediol）and main salts（CoCl₂·6H₂O and Co SO₄·7H₂O）on the morphology,elemental composition,and corrosion resistance of electrodeposited Co-P coatings were evaluated.The results show that the introduction of SA into the Ethaline system containing CoCl₂·6H₂O can significantly improve the surface microcracks of the coating and increase the P content of the coating,which is beneficial for obtaining Co-P plating.With the introduction of 6 m M SA,the electrochemical reduction of Co（II）in the Ethaline system is promoted,the nucleation rate of Co-P nanocrystals is accelerated,and the nucleation mode changes from 2D/3D progressive nucleation to 3D transient nucleation.The micro-cracks on the coating surface gradually improved with the increase in SA content,and the grain size and roughness of the coating also decreased.However,when the addition amount was greater than 12m M,the effect of SA was gradually negative.The P content in the coating was positively correlated with the increase of the SA content;that is,when the SA content increased from 0 m M to 20 m M,the P content in the coating increased from 5.1 at.%to 20 at.%,and the coating structure changed from crystalline to amorphous.The addition of 12 m M SA resulted in dense and amorphous Co-P coatings.And the corrosion current density of the coatings in 3.5 wt.%Na Cl solution was 0.53μA·cm^-2,and the corrosion resistance of the coatings was nearly 10 times higher than that of the Co-P coatings without SA addition(5.08μA·cm^-2).It shows excellent protection and corrosion resistance to Q235 carbon steel in a long-term immersion test.（2）The influence of the water content in the Ethaline-CoCl₂-Na H₂PO₂ electrolyte on the morphology,species composition,and catalytic performance of electrolyzed Co-P prepared by electrodeposition was investigated.The results show that the electroreduction of Co-P is promoted as the water content in the system gradually increases,but it is also accompanied by more severe hydrogen reduction.The introduction of water changed the solvent environment of the system and interfered with the formation of Co（II）-Cl complexes.The introduction of an appropriate amount of water（15 wt.%）caused the phase of the deposited material to change from pure Co to Co（OH）₂and cobalt phosphate hydrate,and its microscopic morphology changed from nanosheet-stacked spherical to dendrite-stacked coral tree.In addition,the introduction of 15 wt.%water is detrimental to the electrocatalytic water evolution（HER）performance of Co-P electrode materials,while it can promote its oxygen evolution（OER）performance to a certain extent.The long-term stability test showed that the OER overpotential partial pressure and bubble adhesion of the Co-P thin film electrode with 15 wt.%water deposition at 30 m A·cm^-2 current density were significantly better than those of the Co-P thin film electrode with no water addition deposition.The structure analysis showed that the introduction of water into the system caused the formation of a large number of OER active substances on the surface of the Co-P electrode.During the OER process,the structure is transformed through the formation of a finer hexagonal prism structure,which is conducive to the gas diffusion of the electrode material and improves the gas phobicity of the electrode surface to improve the catalytic activity and stability of the electrode.