• Citer

Electrochemical deposition of gold from the choline chloride – ethylene glycol deep eutectic solvent

par Nguyen, Van Trang
Président du jury Ustarroz Troyano, Jon
Promoteur Doneux, Thomas
Co-Promoteur Lam, Tran Dai
Publication Non publié, 2025-07-08

Thèse de doctorat

• Accès en ligne
• Détails
• Contenu
• Statistiques

Résumé :

This thesis presents a comprehensive investigation into the electrodeposition of gold from the choline chloride - ethylene glycol (ChCl-EG) deep eutectic solvent, with a focus on understanding the gold redox behavior, the nucleation and growth mechanisms, and the influence of specific additives. The study aims at contributing to a sustainable, cyanide-free alternative for gold plating, motivated by the environmental and health hazards associated with conventional cyanide-based baths.The first part of the research systematically examines the electrochemical properties of gold precursors (AuCl and HAuCl4) in ChCl-EG on glassy carbon and platinum electrodes using cyclic voltammetry, chronoamperometry and electrochemical quartz crystal microbalance (EQCM). The results demonstrate distinct differences in nucleation behavior, diffusion coefficients, and electron transfer numbers between Au(I) and Au(III), with evidence of both progressive and instantaneous nucleation pathways, as well as a comproportionation phenomenon in certain systems. The reduction of HAuCl4 on the glassy carbon electrode proceeds via a two-step mechanism involving an intermediate Au(I) species, whereas on the Pt electrode, the reduction occurs directly from Au(III) to metallic Au(0). Furthermore, EQCM results reveal that the comproportionation reaction occurs only in HAuCl4-containing solutions and is absent in those containing AuCl.In the second part, the effects of two additives - mercaptosuccinic acid (MSA) and 5,5-dimethylhydantoin (DMH) - are explored. MSA forms strong complexes with gold ions, significantly altering the redox potentials of the involved couples, decreasing the diffusion coefficients, and stabilizing the Au(I) and Au(III) species. Even at low concentrations, MSA causes pronounced changes in the electrochemical properties of the systems. Its impact is considerably greater in AuCl-based solutions than in those with HAuCl4, likely due to MSA stronger complexation with Au(I) compared to Au(III). In contrast, DMH shows minimal impact on electrochemical responses, indicating a weak interaction with gold in the deep eutectic solvent. Electron transfer numbers and EQCM data confirm these contrasting behaviors.The final part evaluates the feasibility of applying deep eutectic solvents in immersion gold plating processes such as Electroless Nickel Immersion Gold (ENIG). Specifically: (i) Au(III) species exhibit a higher deposition rate than Au(I); (ii) HAuCl4 enables a higher plating rate than AuCl3; (iii) for AuCl-based systems, the presence of MSA decreases the deposition rate; and (iv) in Au(III) systems, MSAhas distinct effects on HAuCl4 and AuCl3.This thesis provides valuable insights into the electrochemical mechanisms governing gold deposition in deep eutectic solvents and supports their potential as environmentally benign alternatives for future gold electroplating technologies.