Cu-SiO2复合薄膜的电化学过程

Research on Electrochemical Process of Cu-SiO2 Composite Film

目前有关凝胶薄膜电化学形成机理的研究较少。以醋酸铜、正硅酸乙酯和柠檬酸钠在室温下配制了nCu2+∶nCit3-为1∶2,pH值为5.2,nCu2+∶nSi分别为3∶7,2∶8和1∶9的澄清透明的复合溶胶(Sol 1,Sol 2,Sol 3);以这3种复合溶胶为电解液,采用恒电位沉积法在氧化铟锡(ITO)电极上制备了Cu-SiO2凝胶薄膜,并用X射线衍射仪(XRD)、扫描电镜(SEM/EDS)对薄膜进行表征;采用循环伏安法(CV)、交流阻抗技术(EIS)和计时安培法(CA)研究了复合薄膜的沉积机理。结果表明:在沉积电位范围内得到Cu-SiO2薄膜;在低电位下,Cu在Sol 1和Sol 2中的沉积过程为电化学控制,随着电位负移,电化学控制和Cu(Ⅱ)扩散控制同时存在,且Cu(Ⅱ)扩散控制起主要作用。反应电阻随着电位负移先减小再增大,反应电阻增大可能与ITO电极表面凝胶膜的形成有关。Sol 3中,研究电位下同时存在电化学控制和Cu(Ⅱ)扩散控制,且随着电位负移,Cu(Ⅱ)扩散控制也占主要作用。反应电阻随着沉积电位负移一直增大;研究电位下,Cu在溶胶中的电结晶过程遵循三维瞬时成核(3DI)生长机理。

Three stable transparent composite sols with various molar ratios(nCu2+∶nSi)of 3∶7,2∶8 and 1∶9 were prepared using copper acetate,sodium citrate and tetraethyl-silane at room temperature,respectively,which possessed the pH value of 5.2 and the Cu2+/Cit3-ratio of 1∶2.Subsequently,three kinds of composite films were prepared directly on the ITO electrode by potentiostatic electrodeposition method using the above sols as electrolytes,and X-ray diffractometer(XRD)and scanning electron microscopy(SEM/EDS)were employed to analyze the composite films.In addition,the deposition mechanism of composite films was studied by cyclic voltammetry(CV),chronoamperometry(CA)and electrochemical impedance spectroscopy(EIS).Results showed that a Cu-SiO2 film was prepared at deposition potential.At the low potential,the deposition process of Cu in Sol 1 and Sol 2 was electrochemically controlled.As the potential shifted negatively,the process was controlled by electrochemistry and Cu(Ⅱ)diffusion,and the latter played a dominant role.When the potential changed negatively,the reaction resistance decreased firstly and then increased,and the increase of reaction resistance might be related to the formation of gel film on the surface of ITO electrode.In Sol 3,the electrochemical control and Cu(Ⅱ)diffusion control existed at all potentials,and Cu(Ⅱ)diffusion also played a dominant role with the negative shift of potential.The reaction resistance increased as the potential turned negative.Furthermore,under the applied potential,the nucleation mechanism of Cu in sols belonged to the instantaneous nucleation with three-dimensional growth(3DI).