碱性锌酸盐体系中Zn的电沉积行为研究简

通过循环伏安、计时电位及电化学阻抗谱技术研究了碱性锌酸盐体系中Zn的阴极还原历程,采用计时电流法结合扫描电镜(SEM)研究了Zn的电化学成核机理。结果表明:溶液中Zn主要以Zn(OH)42-形式存在,Zn(OH)42-通过前置转化反应生成Zn(OH)2;Zn(OH)2在阴极界面上分两步放电,第一步放电后生成Zn(OH)ad吸附在电极表面,而后经第二步放电还原为Zn,两步均不可逆。外加电位为-1.40~-1.50 V时,体系中仅发生Zn(OH)2的第一步放电反应;电位负移至-1.60 V时,Zn(OH)2经历了两步放电过程,但Zn仅吸附在电极表面,电沉积过程处于一种非稳态;当电位负移至-1.70~-1.80 V时,吸附态Zn才持续进入晶格形成完整镀层。体系中Zn的电结晶过程遵循三维连续形核方式。

Electrodeposition Behavior of Zinc in Alkaline Zincate Electrolyte

The cathodic reduction process of Zn in alkaline zincate electrolyte was studied by cyclicvoltammetry (CV), chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS), while the electrochemical nucleation behavior of Zn was also characterized by using chronoamperometry (CA) and scanning electron microscope (SEM) techniques. The results indicated that Zn existed in the electrolyte in the form of Zn(OH)₄^2-, through a preceding reaction which then transformed into Zn(OH)₂ during electrodepositing. As the species directly discharged on the cathode surface, the discharge of Zn(OH)₂ is a two step-process, by the first step Zn(OH)_ad was produced and adsorbed on the surface of cathode, and then was reduced to Zn by the second step. The two steps of reduction of Zn(OH)₂ were all nonreversible reaction. It is beneficial to the electrodeposition of Zn when the applied potential reduces. The first discharge reaction of Zn(OH)₂ occurred when the applied potential was at -1.40~-1.50 V. The two discharge reactions of Zn(OH)₂ were both occurred in the alkaline zincate system when applied potential reduced to -1.60 V but in this case, Zn atoms only adsorbed on the cathode surface and the electrodeposition process was in a non-steady state. The adsorbed Zn could finally electrocrystallized to form a uniform Zn coating only when the applied potential reduces to -1.70~-1.80 V. The electrocrystallization of Zn from alkaline zincate electrolyte may follow a three-dimensional progressive nucleation mechanism.