The effects of thiourea (TU) on the kinetics and electrochemical nucleation of tin from stannous chloride bath in acidic medium have been investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry. CV results showed that the tin reduction is a one-step reaction and indicated that TU inhibited the reduction of tin ions at high concentration. EIS analysis showed that the electrodeposition process of tin is affected by the addition of TU. The nucleation mechanism of tin was studied using both Sharifker-Hills (SH) and Palomar-Pardavé (PP) models. SH model indicated that hydrogen evolution and tin reduction occurred simultaneously. Non-dimensional current-time transients curves based on PP model revealed that the tin nucleation followed 3D progressive mechanism without TU and with 0.01 M TU, while the nucleation process changes to 3D instantaneous in presence of 0.1 M TU. However, at 1 M TU, the nucleation mechanism is located between instantaneous and progressive model. The proton reduction reaction was inhibited at all concentrations of TU. Quantitative determination showed that in the presence of TU, the diffusion coefficient of tin species, the hydrogen evolution rate constant, the nucleation rate constant and the number of active sites were decreased.

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