Initial Stages of Sn Electrodeposition on Glassy Carbon Electrodes in Acid Solutions. Effect of Temperature and Thiourea Addition

L.A. AZPEITIA; A.E. BOLZÁN; C.A. GERVASI

Providence

Congreso; 68th Annual Meeting of the International Society of Electrochemistry- Electrochemistry without borders; 2017

International Society of Electrochemistry

Among other uses, Sn has been proposed as anode material for lithium batteries, particularly because of its excellent intercalation properties for lithium ions. An interesting possibility is the development of carbon based electrodes, such as graphite or graphene, coated by Sn. In order to advance in the knowledge of the electrodeposition of Sn on carbon substrates, we have studied the electrodeposition of Sn on glassy carbon (GC) electrodes between 283 and 338 K C in sulphuric acid solutions in the absence and the presence of thiourea, (TU) employing voltammetric runs, potential steps and electrochemical impedance spectroscopy coupled with SEM analysis. The voltammetric runs show a single cathodic current peak that moves to less positive potentials as the TU concentration is increased, and, at the same time, the threshold potential for the hydrogen evolution reaction decreases. The analysis of the current transients related to the electrodeposition of Sn at constant potential show that the corresponding current peaks moves to longer times in the presence of TU along with a change in the nucleation mechanism. Thus, in the absence of TU, the adimensional analysis of the current transients fit a model associated to an instantaneous nucleation and 2D growth under diffusion control. The presence of TU in the platting solution apparently changes the mechanism to a progressive nucleation process, seemingly due to the adsorption of the molecule blocking active surface sites. The SEM images show that Sn particles deposited from TU-free solutions exhibit a rather cubic form with a mean size of about 2x10-9 cm2, and are well distributed on the electrode surface. Conversely, deposits formed from TU-containing solutions exhibit comparatively very large and dispersed particles, particularly at the lowest temperature. It is also possible to observe the presence of dispersed aggregates formed by rather large sticks at right-angle. The Nyquist plots obtained in TU-free solutions between 60 kHz and 10 mHz, show two time constants at high frequencies followed by an inductive loop, assigned to the relaxation of an adsorbed species, and finally a Warburg impedance at low frequencies, which is related to the transport of ions to the reaction interface. On the other hand, Nyquist plots obtained in TU-containing solutions exhibit a single time constant, at least in the 60 kHz ? 10 mHz frequency range