The Preparation Of Composite Sols And Electrochemical Formation Of Composite Films For Copper-silica

In this work,Cu（Ⅱ）-SiO₂ composite sols with different compositions were prepared.Cu-SiO₂ composite film were prepared by potentiostatic electrochemical method using Cu（Ⅱ）-SiO₂ composite sol as electrolyte.The electrochemical formation mechanisms of prepared films were studied.Three serials of stable Cu（Ⅱ）-SiO₂ composite sols with different pH values（I）,different ratio of n_Cu²⁺:n_SiO2（Ⅱ）and n_Cu²⁺:n_Cit^3-（Ⅲ）were prepared using Cu（Ac）₂ as copper source,TEOS as silicon source,Na₃Cit as complexing agent.The distributions of Cu（Ⅱ）complexes in different sols were also analyzed.Composite films were deposited on ITO conductive glass using as-pereapred composite sols as electrolytes.The deposited films were characterized as Cu-SiO₂ by X-ray diffraction（XRD）.The formation mechanisms of composite films were studied by various electrochemical techniques.The results of cyclic voltammetry（CV）,linear sweep voltammetry（LSV）and electrochemical impedance spectroscopy（EIS）indicated that Cu（Ⅱ）reduced to Cu by one-step reaction.SiO₂ deposited inducely at the same time.Chronoamperometry（CA）results showed that the electrocrystallization of Cu in the sols followed instantaneous nucleation mechanism.In the composite sols I,the deposition potential of Cu shifted negetively with the increase of the pH value of the sol,because the different types of Cu（Ⅱ）complexes in the sols of different pH values.In the sol of lower pH,there were many[Cu₂Cit₂H_-1]^3-ions which were easy to discharge.The reaction resistance increased significantly with the increase of overpotential.In the sol of larger pH value,they were mainly[Cu₂Cit₂H_-2]^4-ions which were difficult to be reduced.Smaller reaction resistance occurred at a higher potential.In the composite sols with pH of 6.30,there were a lot of[Cu₂Cit₂H_-2]^4-and Cit^3-ions.The concentration of[Cu₂Cit₂H_-2]^4-ions and free Cit^3-ions increased with the increase of the ratio of n_Cu²⁺:n_SiO2.Larger concentration of the[Cu₂Cit₂H_-2]^4-ions led to the increase of electrodeposition current.Free Cit^3-ions increased in reaction resistance.The electrodeposition of Cu was controlled by the diffusion coefficient at higher overpotentials.In the composite sols with pH of 5.20,the main ions were[Cu₂Cit₂H_-2]^4-and[Cu₂Cit₂H_-1]^3-ions in sols of n_Cu²⁺:n_Cit^3-with 1:2 or 1:1.In the sol of the ratio with 2:1,the main ions were[Cu₂CitH_-1]ions.At lower overpotential,the reaction resistance decreased with the increase of the ratio of n_Cu²⁺:n_Cit^3-,because the concentration of Cu²⁺ions increased.At higher overpotentials,the reaction resistance increased.