Propriedades eletrocatalíticas e anticorrosivas de revestimentos de ZnCo obtidos em meio de solvente eutético

Abstract

The performance of Zn, Co and Zn-Co coatings in RDH electrocatalysis was evaluated using Tafel parameters calculated from LSV experiments in 1 mol L−1 KOH at 0.5 mV s−1 and 298 K. The Zn and Zn-Co films were electrodeposited from electrolytic solutions prepared using a deep eutectic solvent based on choline chloride (ChCl) and ethylene glycol (EG) in molar ratio of 1:2 (ChCl:2EG), varying the concentrations of Zn2+ and Co2+ ions from 0 to 0.4 mol L−1. The substrate used was Cu and the deposition mode was potentiostatic at −1.3 V and 343 K. The cyclic voltammograms showed characteristic processes of reduction and oxidation of metals in ChCl:2EG. The Zn2+ diffusion coefficients varied between 8.93 (± 0.77) × 10−11 cm2 s−1 (303 K) and 4.55 (± 0.34) × 10−10 cm2 s−1 (343 K). The diffusion coefficients determined for Co2+ varied between 2.64 (± 0.07) ×10−7 cm2 s−1 (303 K) and 4.43 (± 0.48) ×10 −7 cm2 s−1 (343 K). The apparent activation energy (Ea), calculated from ln D graphs as a function of the inverse of the absolute temperature, for the diffusion of Zn2+ and Co2+ ions was 35.93 kJ mol−1 and 11.07 kJ mol−1, respectively. The SEM images showed that the increase in the amount of Co in the coatings led to the formation of cracks, favoring the use of the alloys as electrocatalysts. Furthermore, a close correlation was observed between the composition of the electrolyte solution and that of the electrodeposits. The Zn and Zn-Co films showed electrocatalytic activity against RDH in an alkaline medium, with Tafel coefficients of 170.28 mV dec–1 and overpotential, at 10 mA cm–2, of −641 mV for Zn; 123.50 mV dec–1 and −494 mV for the Zn96Co4 alloy and 113.46 mV dec–1 and −377 mV for the Zn3Co97 alloy. Regarding the Zn, Co and ZnCo coatings in the corrosion study, in a medium of NaCl 3.5% m/m, voltammograms were obtained, on a 1020 carbon steel substrate, in DES ChCl:2EG as solvent, varying the concentrations of Zn2+ and Co2+ ions from 0 to 0.4 mol L−1. The potentiostatic mode was used, applying a potential of −1.4 V at 343 K. The morphological characterization of the electrodeposit surface was carried out using SEM and the distribution of the metals Zn and Co was determined by EDS. The polarization curve tests of the species obtained at 293K, on a 1020 carbon steel substrate, with concentrations ranging from Zn2+ and Co2+ from 0 to 0.4 mol L−1. It was observed that, in comparison with 1020 carbon steel, the Zn coating presented a higher corrosion current, due to the sacrificial nature of Zn in relation to steel.