Mechanism and Kinetics of Chromium Electrochemical Nucleation and Growth from a Choline Chloride/Ethylene Glycol Deep Eutectic Solvent

Abstract

The nucleation and growth of chromium onto glassy carbon electrode from Cr(III) ions dissolved in a deep eutectic solvent, composed by a mixture of choline chloride and ethylene glycol were studied. From both potentiostatic and potentiodynamic methods, it was evidenced that Cr electrodeposition, from Cr(III) ions, takes place through two stages: firstly, from Cr(III) to Cr(II), forming soluble species, followed by reduction from Cr(II) to Cr(0). It was found that the Cr electrodeposition kinetics and mechanism are different depending on whether it is occurring from Cr(III) or from Cr(II) ions. From analysis of the potentiostatic experimental current density transients, new models were proposed to explain the chromium nucleation and growth in these initial conditions. These models involve contributions to the overall current due to: an adsorption process, diffusion of Cr(III) ions to the electrode surfaces to form Cr(II) ions, Cr 3D nucleation and diffusion-controlled growth and residual water reaction over the growing surfaces of the Cr nuclei. The proposed models help determining the charge percentage due to each individual contribution to the total process. Scanning electron microscopy and energy dispersive spectroscopy were used to determine the morphology and the elemental composition of the deposit respectively.

Influence of water content and applied potential on the electrodeposition of Ni coatings from deep eutectic solvents

“…1(b)) and reaches a plateau. This phenomenon indicates the contribution of additional electrochemical processes into the overall current, similar to what has been reported previously for the electrodeposition of cobalt with concomitant proton reduction [54] or, more recently, for the electrodeposition of chromium from a choline chloride-ethylene glycol DES with concomitant reduction of water [55]. In the present manuscript, the current arises from the reduction of water on the Ni growing centers.…”

Factors Affecting Nucleation and Growth of Chromium Electrodeposited from Cr3+ Electrolytes Based on Deep Eutectic Solvents

“…The values of α = 0.19 and D = 8.5 ×10 -7 cm 2 s -1 were obtained from the slopes of E p vs. ln ν and j p vs. ν 1/2 plots, respectively. The value of D is slightly lower than the reported value 3.5×10 -6 cm 2 s -1 obtained in 0.05 mol dm -3 Cr 3+ /EG-DES at 70 o C [26] and this result is logical due to lower temperature (30 o C) and high viscosity of electrolyte used here in our experiment.…”

“…The kinetic parameters , , A, N 0 and AN 0 are also calculated based on these constants. As presented in Table 1a, the average diffusion coefficient of Cr 3+ is 5.7 ×10 -7 cm 2 s -1 and that of Cr 2+ is 2.515×10 -7 cm 2 s -1 which is slightly lower than the results reported by Mejía-Caballero I et al [26].…”

“…Ethylene glycol (EG) and urea (U) have been used as HBDs with ChCl to obtain their relevant DES used to electrodeposit Cr from. Seldom reports have explored the mechanism and kinetics of Cr electrodepostion from these solvents [25,26], which are very important to get the knowledge about the optimum conditions for the desired performance.…”

Chromium electrodeposition using electrolytes based on trivalent chromium compounds: a review

“…Åêñïåðèìåíòàëüíî äîñë³äaeåíî ïðîöåñ åëåê-òðîõ³ì³÷íî¿ íóêëåàö³¿ õðîìó íà ñêëîâóãëåöåâîìó êàòîä³ ïðè îñàäaeåíí³ ìåòàëó ç åëåêòðîë³òó íà îñíîâ³ åâòåêòè÷íî¿ ñóì³ø³ õîë³í õëîðèäó òà åòèëåíãë³êîëþ [164]. Ðîçðîáëåíî ê³íåòè÷íó ìîäåëü, ÿêà âðàõîâóº ñòà䳿 äèôó糿 ³îí³â Cr(III) äî åëåêòðîäíî¿ ïîâåðõí³, àäñîðáö³¿, ïåðåíåñåííÿ çàðÿäó, 3D íóêëåàö³¿ òà ðîñòó êðèñòàë³â.…”