A possible channel effect of the organics adsorbed to the electrode surface on interfacial electron transfer in the alkaline Pb electrodeposition process

Abstract

In this paper, the mechanism of electron transfer (ET) in alkaline lead electrodeposition at 353 K was put forward based on the lower cell voltage, weaker polarization, less negative shift of the cathode peak, and lower charge transfer resistance using 1-benzyl-3-carboxyl-pyridinium (BCP) chloride as an additive, compared with 1-benzyl-3-methyl-pyridinium (BMP) chloride and gelatin. Namely, BCP possesses a π-bond system and a terminal charged group, which captures the Pb(OH)₄²⁻ species by complexation and tethers (see ²⁰⁷Pb-NMR spectroscopy and Raman spectroscopy) the metal ion to the active site of the cathode surface. BCP's positive heteroaromatic ring is adsorbed on the negative cathode (see XPS), and then forms a metal–molecule–metal ion molecular-bridge. The molecular-bridge consisted of a coherent conjugated π-bond, opening a channel for interfacial ET as the delocalization of the π-bond electron. The π-bond system of BCP can improve the ET facilitation compared with the δ bond system of BMP, and the ET resistance was reduced and the cell voltage was decreased relatively. Additives that can coordinate to the metal ion species and form a coherent conjugated system are considered to be used in industrial hydrometallurgy. The smoothing mechanism of the additive to the deposited product is also clarified at the same time.