The Research Of The Process And Performance Of Electrodepositing Gold In The Ionic Liquid [BMIm][BF₄]

Gold deposits have numerous excellent physical and chemical properties,such as the golden yellow appearance,excellent electrical conductivity,topping thermal conductivity and outstanding chemical stability,and they are widely used in many fields.Nowadays,cyanide baths,which contain toxic cyanide,are the most widely used gold electroplating.It is essential to develop a non-toxic gold electroplating of excellent properties.In this work,aqueous solutions were replaced by ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate?[BMIm][BF4]?as the solvent,and the appropriate complex agent and additive were added to the electrolyte.The optimized gold electroplating was confirmed with the contrast of the properties of electrolytes and deposits,which contained 0.050 mol·L^-1 HAuCl₄·3H₂O,0.30 mol·L^-1 5,5-dimethylhydantoin?DMH?and 20 mmol·L^-1 2-aminopyridine.The temperature was 328 K;the current density was 3.5 mA·cm-2,and the stirring speed was 500 rpm in electrodeposition.The golden-yellow gold deposit with refined grains and excellent conductivities can be obtained in ionic liquid [BMIm][BF4] containing HAuCl₄·3H₂O and DMH and 2-aminopyridine.The electrolytes were chemically stable.The deposition rate was 4⁵ ?m·h-1,and the cathodic current efficiency was 100% under the optimized process conditions.However,the coverage ability of the electrolytes was relatively poor.The influences of DMH and 2-aminopyridine were studied by the linear sweep voltammetry?LSV?.The gold complexes Au?DMH?4-,Au?DMH?2-can be formed by DMH and Au³⁺,Au+,and the surface convert process was inhibited in the reduction process.The addition of DMH increased the cathodic polarization,which can brighten gold deposits and refine crystal grains of gold deposits.2-Aminopyridine was absorbed on Au nuclei,which inhibited the reduction process of Au.The addition of 2-aminopyridine had synergistic effects with DMH on brightening gold deposits and refining crystal grains.Cyclic voltammetry?CV?was used to investigated the electrochemical behavior on different working electrodes in electrolytes.The reduction of Au³⁺ to Au on GCE had a two-step reduction process.The first reduction process was Au³⁺ to Au+,and the second process was Au+ to Au.Besides the two above-mentioned reduction processes,the reduction of Au³⁺ contained the third process when the working electrode was Au and Pt electrode,respectively.This process may correspond to the reduction of gold complexes on specific crystal faces of Au and Pt electrode,which were exposed in electrolytes.Au can be oxidized in the electrolyte when glassy carbon electrode,Au and Pt electrode were used as the working electrode.The processes were of the oxidation of Au to Au+ and the oxidation of Au+ to Au³⁺ successively,which were the same on the different electrodes.Besides,the addition of DMH and 2-aminopyridine did not bring side reactions.The kinetic parameters and the nucleation process of gold were investigated.The transfer coefficient ? of the reduction of Au³⁺ to Au+ was 0.24 in different electrolytes,where were not changed by DMH and 2-aminopyridine nearly.The diffusion coefficient D of gold complexes were 6.699×10-7,6.269×10-7,5.118×10-7 cm2·s-1 in bath containing HAuCl₄·3H₂O,containing HAuCl₄·3H₂O and DMH,containing HAuCl₄·3H₂O and DMH and 2-aminopyridine,respectively.The diffusion coefficient D decreased with adding DMH and 2-aminopyridine,which was related to the formation of gold complexes and the increased viscosity of baths.The transfer coefficients ? were 0.136 and 0.146 respectively when Au,Pt electrode were used as the working electrode,and the diffusion coefficients D were 1.729×10-6,1.840×10-6 cm2·s-1.It revealed that the diffusion processes of gold complexes were easier on the surfaces of Au and Pt electrode.The reduction of Au³⁺ to Au+ and Au+ to Au were jointly controlled by the diffusion process and the electrochemical process,and the two reduction processes were irreversible.The nucleation process of gold were studied by chronoamporometry.The nucleation methods were progressive on GCE,which were not influenced by the addition of DMH and 2-aminopyridine.