Effects of Deposition Potential and Temperature on Co(II) Reduction and Electrocrystallization for Preparing Nanocrystalline Co Coatings in Ethylene Glycol Solution

Abstract

Based on cyclic voltammetry (CV) and chronoamperometry (CA) experiments, the effects of deposition potential and temperature on Co(II) reduction and electrocrystallization in ethylene glycol (EG) are reported. CV observations show that Co(II) reduction reaction is irreversible, and both the equilibrium potential and nucleation overpotential, ηnucleation, move to more positive values as the temperature is improved. The diffusion coefficient of Co(II) is 2.24 × 10-6 cm2 s-1 at 323 K and the activation energy for bulk diffusion (Ebd) of Co(II) is 22.03 ± 0.8 kJ mol-1. CA observations show that the Co electrocrystallization mechanism is a 3D nucleation and growth of a new phase under diffusion control. Its mechanism is an instantaneous regime at 323 K at various applied potentials, however, the mechanism changes from a progressive nucleation to an instantaneous nucleation at -1.10 V as the temperature increases. The cobalt nuclei are spherical microstructure, and these innumerable spherical crystal particles can align compactly to form many wirelike crystals bundles. XRD observation confirms the characteristic peak of crystalline Co with a preferred orientation direction and the average size of Co grains is 19 nm. It is also found that the Co coating thickness is affect by the potential and temperature.

Co-deposition of Co–Ni alloy catalysts from an ethylene glycol system for the hydrogen evolution reaction

“…Therefore, all these current densities at the various applied potentials can decrease and tend to level off. 27 In order to further clarify the mechanism of the Co-Ni alloy nucleation and growth process, non-dimensional (j/j max ) 2 vs. (t/t max ) curves deduced from the Sharier-Hills model 38,39 was employed based on eqn (1) and ( 2) from current-time transient curves and exhibited in Fig. 3b.…”

Pure pompon structured Co–Mo alloy electro-deposited from ethylene glycol solution and used as electrocatalysts for hydrogen evolution reaction

“…EG (≥ 99.5%), anhydrous CoCl 2 (99.7%) and Na 2 MoO 4 (≥ 99.5%) were obtained from Aladdin Bio-Chem Technology Co., Ltd (Shanghai). Before using, all the above three reagents were dried based on the previous literatures [36,37]. All other chemicals and reagents used in this study were commercially available and of an analytical reagent grade.…”

“…In recent years, the electrodeposition of Co and Co alloys (including Co-Mo alloys) from nonaqueous systems such as ionic liquid (IL) system, organic solvent, and the mixture of IL and organic solvent, has received intensive interest as reported in several literatures [24,[36][37][38][39][40][41] due to the fact that these techniques could eliminate the necessity to employ additional complexing agents, improve current e ciency, and obtain more variety of materials with better property compared with traditional aqueous systems. For instance, the Co and Co-Al alloys coatings without microcracks had been successfully prepared by Carlin et al [41] from the 1.5:1.0 AlCl 3 :1-ethyl-3-methylimidazolium chloride room temperature molten salt.…”

“…It should be noted that many microcracks could also be observed on the obtained Co-Mo alloy coating surface. Although a few of literatures about Co and Co alloy lms electrodeposited from organic solvents including such DMF [42], DMSO [43] and EG [37] have been published, the literatures about the Co-Mo alloy coatings prepared from organic solvents have been published hardly in previous literatures.…”

“…In our previous works, nanocrystalline Co coating with spherical crystal particles forming many wirelike crystals bundles was prepared from EG system [37]. Subsequently, both the nanocrystalline Co [36] and Co-Ni alloy [24] catalysts were electrodeposited from the [EMIM]HSO 4 -EG system, and they exhibited a better catalytic activity and stability for HER.…”