Multifaceted insights into Au coatings electrodeposited from a ChCl-EG based Deep Eutectic Solvent (DES): Unravelling the effect of surfactant polarity and current density on the morphology, mechanical properties, and anti-tarnishing efficacy

In the present work, the effect of surface polarity of cationic, anionic, and non-ionic surfactants on the structural, mechanical and anti-tarnishing efficacy of Au coatings electrodeposited from a ChCl-EG based bath is investigated. X-ray diffraction studies and first-principles calculations reveal that both cationic and anionic surfactants tend to get adsorbed on other facets rather than (111), effectively facilitating the growth of Au along (111) planes during the electrodeposition. In the presence of CTAB, the electrodeposited Au layer has a smooth surface with almost a globular morphology. However, in the presence of SDS, the morphology of the Au coating changes from globular to sharp-edged facets. In the presence of PVP, the Au coating has an irregular faceted type morphology. The anti-tarnishing efficacy of the coatings is determined using EIS and static immersion tests. The findings reveal that in the presence of cationic and anionic surfactants, the Au coatings have better resistance to tarnishing in a sulphide medium. Therefore, a strategy for developing tarnishing-resistant Au coatings via electrodeposition involves the control of surface morphology, which is well facilitated by using proper surfactants.