| Electron transfer (ET) has belonged to heart of kinetics of reaction. ET occurred at interface is strongly dependent on the structure of interface. Investigation of ET occurred in the metal-solution interface can help us to understand the basic electrochemical behavior in the process of metal species electrodeposition. In the alkaline media, the investigation of effect of additive on interfacial ET in process of Pb electrodeposition can provide information for choosing additive used in electrodeposition process, additionally, such Pb electrodeposition in alkaline media with less pollution also meets the currently industrial Pb hydrometallurgy requirement for environment protection.In the process of electrodeposition of lead in alkaline media, ET occurred at metal-solution interface was investigated in this paper. At the same time, the effects of industrial additives JZ-04, sodium lignin sulfonate (SLS), gelatin, ionic liquids compounds 1-benzyl-3-carboxyl pyridinium (BCP) chloride and 1-benzy 1-3-methyl pyrdinium (BMP) chloride on Pb electrodeposition, such as cell voltage, polarization and morphology of electrodeposit were investigated. The effects of BCP and BMP on ET mechanism in alkaline electrolyte are reported. The experimental results indicate that the addition of JZ-04 or BCP into blank electrolyte has a very little effect on cell voltage and polarization. The electrodeposit obtained from electrolyte with JZ-04 or BCP rather than with SLS, gelatin and BMP is smoothest. However, BMP with same molecular length with BCP causes a huge increase of cell voltage and polarization.According to the experiments of linear sweep voltammetry, potentiodynamic polarization, cyclic voltammetry and electrochemical impedance spectroscopy (EIS) combined with X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM), the model of effects of additive on ET is put forward. Firstly, ET is controlled by the electron tunneling mechanism. The tunneling probability increases with the decrease of tunneling distance. When additive is added into blank solution, a selectively physical adsorption of additive to active salient of cathode surface will occur. The tunneling distance becomes larger and ET becomes difficult. Therefore the cell voltage and ET resistance increase. But BCP with a terminal hydrophilic charged group -COO captures Pb(OH)4 2- species by coordination and makes it close to cathode surface.The tunneling distance becomes short. Additionally, BCP forms metal-molecule-metal ions molecular-bridge between cathode and Pb(OH)42- due to its adsorption and coordination. This molecular-bridge consisted of coherent π bond opens channel for electron transfer. Thus ET through molecular-bridge is promoted. While BMP with a hydrophobic methyl -CH3 cannot form molecular-bridge because-CH3 will not coordinate to Pb(OH)42-Therefore a distinct electrochemical difference between the cases of BCP and BMP occurs.Additionlly, by using MS,13C-NMR,’H-NMR, and IR, in this paper the component of industrial additive JZ-04 is characterized and result shows that the substance with BCP structure is primary component. BMP is synthesized in laboratory and characterized by’H-NMR,13C-NMR.Due to that Pb(Ⅱ) species can be extensively hydrolysed in alkaline solution, therefore, by using Raman spectroscopy and 207Pb-NMR combined with XRD, ICPAE, thermogravimetric analysis, in this paper the hydrolysis product of Pb(Ⅱ) species in the electrolyte with or without BCP is proved. The results indicate that it may be not a polynuclear but mononuclear lead complex... |
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