【摘要】 随着电解精炼法制备高纯金技术的发展，导电性好、重量轻且可重复使用的Ti阴极在5N（99.999%）级高纯金电解中得到广泛使用，然而Au在Ti阴极上的电沉积机制尚不明确。本文在NaCl-HAuCl₄溶液中对Au在Ti电极上的电沉积过程及机制进行了研究，使用循环伏安法（CV）研究了[AuCl₄]^-在Ti电极上的还原过程及其动力学，并计算了[AuCl₄]^-在Ti电极表面的传递系数和扩散系数，使用计时电流法研究了Au在Ti电极表面的形核过程。Ti电极在不同溶液和不同电位区间的CV曲线表明，在-0.56和-0.92 V处的两个还原峰分别对应[AuCl₄]^-还原反应和析氢反应，且Au在Ti电极表面的沉积为[AuCl₄]^-→Au一步过程。不同扫描速率下的CV曲线表明，Au的沉积为受扩散控制的不可逆过程，计算得出[AuCl₄]^-在Ti表面的传递系数为0.157，扩散系数为1.16×10^-4 cm²·s^-1。通过对不同电位下的计时电流数据进行分析，并将实际形核曲线和理论形核曲线进行对比，确定Au在Ti表面的形核为三维形核，符合Scharifer-Hills瞬时形核理论。更多还原

【Abstract】 The cathode plate made of Ti has gradually become the main cathode of high-purity gold electrolysis because of the advantages of being lightweight, easy to peel off with the electrolysis Au, reusable, and low cost. So, it is necessary to investigate the electrodeposition mechanism for Au on Ti cathode. The electrodeposition process and mechanism of Au on Ti cathode were investigated in NaCl-HAuCl₄ aqueous solution. Cyclic voltammetry（CV） was used to examine the reduction process and kinetics of [AuCl₄]^-on Ti electrode, and the transfer coefficients and diffusion coefficients of [AuCl₄]^-on the surface of Ti electrode were calculated. Chronoamperometry（CA） was used to examine the nucleation mechanism of Au on Ti electrode surface. The three-electrode system was used for all electrochemical experiments. Ti electrode of 3 mm diameter was used as the working electrode, Pt sheet electrode（2 cm×2 cm） was used as the auxiliary electrode, and a saturated calomel electrode（SCE） was used as the reference electrode. The temperature of the electrolytic cell was maintained at 25 ℃ during the experiment. To examine the electrochemical behavior of Au deposition on Ti electrode, CV tests were carried out in 0.1 mol·L^-1 NaCl+5 mmol·L^-1 HAuCl₄ aqueous solution with a potential scanning range of-1.5～1.5 V and a potential scanning rate of 50 mV·s^-1. Furthermore, the control tests were performed in 0.1 mol·L^-1 Na Cl and 0.1 mol·L^-1 Na Cl+5 mmol·L^-1 HCl aqueous solutions with the same conditions in order to discuss the effects of NaCl and H⁺ on CV curves of NaCl-HAuCl₄ aqueous solution, respectively. The results of the control experiments showed that there was no reduction wave on CV curves in NaCl aqueous solution, while a reduction wave occurs on CV curves obtained in NaCl-HCl aqueous solution at-1.3V, which was attributed to hydrogen evolution on the surface of Ti electrode due to H⁺ addition. This also demonstrated that hydrogen evolution would occur at Ti electrode in aqueous solution containing 5 mmol·L^-1 H⁺ in the potential range of-1.5～1.5 V and lead to the corresponding reduction wave on CV curve. Two reduction waves appeared on CV curve in 0.1 mol·L^-1 NaCl+5 mmol·L^-1 HAuCl₄ solution at-0.56 and-0.92 V, respectively. Moreover, the positive scanning curve intersected with the negative scanning curve at-0.37 V during the back-scanning, and the positive scanning current started to be greater than the negative scanning current, which proved that there was Au deposited on the surface of Ti electrode. As the sweepback potential continued to increase, a corresponding oxidation wave appeared on the sweepback curve, which was attributed to the oxidation of Au deposited. These results indicated that an Au deposition reaction and a hydrogen evolution reaction would occur at Ti electrode in NaCl-HAuCl₄ aqueous solution in the potential interval of-1.5～1.5 V. Consequently, the two reduction waves appearing on CV curve in NaCl-HAuCl₄ aqueous solution corresponded to the reduction of [AuCl₄]^-and H⁺, respectively. An additional CV test was performed in NaCl-HAuCl₄ aqueous solution to investigate the deposition mechanism of Au on Ti electrode further. The endpoint potential in the negative direction of this scan was adjusted to-0.7 V, while the other conditions were kept constant. There was only one reduction wave and the corresponding oxidation wave on CV curve, which indicated that the deposition reaction of Au on Ti electrode occurred before-0.7 V, i.e., the first reduction wave appearing on CV curve in NaCl-HAuCl₄ aqueous solution corresponded to the deposition reaction of Au, the second reduction wave corresponded to the hydrogen evolution reaction, and the deposition of Au was a one-step reduction process of [AuCl₄]^-→Au. CV tests were carried out to investigate the reduction kinetics of [AuCl₄]^-on the surface of Ti electrode in 0.1 mol·L^-1 NaCl+5 mmol·L^-1 HAuCl₄ aqueous solution at different scan rates. The reduction wave potential E_p at different scan rates was linearly related to lgv, and the value of E_p became more negative as the scan rate increased. Concurrently, the reduction wave current density j_p was linearly related to v^1/2. These results indicated that the deposition of Au was an irreversible process controlled by diffusion. The transfer and diffusion coefficients of [Au Cl₄]^-on Ti surface were calculated to be 0.157 and 1.16×10^-4 cm²·s^-1, respectively, based on the data of CV curve obtained at different scan rates. Chronoamperometry tests were carried out at different potentials to investigate the nucleation mechanism of Au on Ti electrode. With the fall of the step potential, the time-current curves start to peak, and the current dropped rapidly after reaching the peak I_m and eventually stabilized. This phenomenon indicated that the nucleation process of Au on Ti surface belonged to three-dimensional nucleation. Comparing the actual nucleation curves with the theoretical nucleation curves, it was determined that the nucleation of Au on Ti surface was three-dimensional and follows the SchariferHills transient nucleation theory.更多还原