Multiple Nucleation Processes during the Platinum Electrodeposition Onto Glassy Carbon Electrodes Influence of the Temperature
Authors: Mendoza Huizar Luis Humberto , Marquez Ricardo 
Published: February 2020

Introduction
The deposition of noble metal particles on some substrates is a field of great interest due the resulting electrocatalytic properties [1, 2]. This is because these particles can exhibit a larger efficient surface area and higher activity [3]. In this sense, Pt nanoparticles deposited on carbon substrates are of special interest [4, 7] due to the low cost, performance and high efficiency. Pt has been electrodeposited onto carbon substrates including highly oriented graphite (HOPG) electrode [6], carbon nanotubes [7], carbon fiber [8], graphite [9], conducting polymers and macroporous carbon [10], glassy carbon [11, 12], among others. In the case of platinum electrodeposition process onto GCE, the information concerning kinetical of the nucleation and growth process is scarce. Therefore, in the present work, we carried out an electrochemical study, in order to understand the Pt electrodeposition process onto this system.
Methodology
Pt electrodeposits onto GCE were carried out from an aqueous solution containing 0.01 M K2PtCl4 at 25, 30, 35 and 40 oC. All solutions were prepared using analytic grade reagents with ultra pure water (Millipore-Q system) and were deoxygenated by bubbling N2 for 15 minutes before each experiment. A 3-compartment electrochemical cell was used in the electrochemical experiments. An Ag/AgCl and graphite bar served as the reference and counter electrode, respectively. A glassy carbon disk of 3 mm of diameter was used as working electrode and polished to mirror–like finish and ultrasonicated before each experiment. The three electrodes remained connected to an EPSILON potentiostat and a personal computer with the BASi-Epsilon-EC software during the experiments to keep them under control and obtain the results.
Results and discussion
Figure 1 shows a set of current density transients recorded at a potential value of -0.010 V at different temperature values. These transients were obtained applying an initial potential 0.600 V on the surface of the GCE electrode. In this Figure, it is possible to observe that at shorter times, there is a falling current transient that can be associated with a process that follows Langmuir adsorption-desorption kinetics [13]. After this falling current, in each case, the j-t plots pass through a first maximum (t < 5 s), and a second maximum (t > 5 s), which corresponds to a secundary nucleation and growth process. Also, note that for the transients obtained at 25 y 30 oC, there is a third maximum, which coresponds a new nucleation and growth process. These transients were fitted to a nucleation model which considers that the total current is given by jT=j1+j2+j3, where j1, j2, and j3 corresponds to the nucleation and growth process of the first, second and third maxima, respectively.
Conclusions
Pt electrodeposition on GCE was studied at different temperatures using potentiostatic and voltammetric techniques. The effect of the temperature effect on kinetics parameters such as diffusion coefficient, and charge transfer coefficient was analyzed. The values of nucleation rate and rate constant of the proton reduction reaction increased with the temperature increment and the applied overpotential. The values of the transfer coefficient was analyzed and a decrease in its value with the temperature increment is observed.

Acknowledgements: LHMH gratefully acknowledges financial support from CONACYT (project CB2015-257823) and to the Universidad Autónoma del Estado de Hidalgo.
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Figure 1