Silver electrodeposition from air and water-stable ionic liquid: An environmentally friendly alternative to cyanide baths Roberta Bomparola, Stefano Caporali ⁎ , Alessandro Lavacchi, Ugo Bardi Dipartimento di Chimica, Università di Firenze and Consorzio Interuniversitario di Scienza e Tecnologia dei Materiali (INSTM) unità di ricerca di Firenze, Via della Lastruccia 3, 50019 Sesto Fiorentino, Italy Received 2 March 2007; accepted in revised form 2 April 2007 Available online 11 April 2007 Abstract The influence of temperature on the kinetics and the morphology of silver deposits obtained from an air and water-stable ionic liquid (the 1- butyl-3-methyl imidazolium tetrafluoroborate) was studied by means of cyclic voltammetry and chronoamperometry. The nucleation and growth mechanisms have been investigated and the effect of temperature evaluated up to 200 °C. Dense, pure and very thin (about 0.3 μm) silver coatings, with decorative properties, have been obtained on commercial copper electrodes at different temperatures. The characterization of the deposits morphology has been performed by visual investigation and SEM microscopy. Data about thickness were acquired by Calotest® measurements. The deposits result constituted by pure silver as determined by combination of EDX microanalysis and Auger Electron Spectroscopy (AES). The deposition method promises to be a new, environmentally friendly, method for silver electrodeposition which is the reason for the absence of cyanide and volatile toxic solvents in the electroplating bath. © 2007 Elsevier B.V. All rights reserved. Keywords: Ionic liquids; Silver; Electrodeposition; Nucleation mechanism; Cyanide free bath 1. Introduction There exist countless industrial applications where different chemical and physical techniques have been applied in order to produce a thin and homogeneous coating onto a metal, or an alloy, in the intent to improve their chemical and physical properties. Silver is one of the metals which has been more intensively used for coatings [1,2] especially in very thin layers. It shows excellent physiochemical and antibacterial properties, very good corrosion resistance, high bulk conductivity and excellent features for decorative purposes. Industries in fields such as microelectronics, aerospace, automotive and jewelries need homogeneous, thin and good looking silver layers which can be cheaply deposed onto a less noble substrate. Numerous methods have been proposed and patented on the basis on electro- and electroless plating. Also vacuum techniques such as chemical or physical vapour deposition, have been proposed, even though these methods present several drawbacks, such as difficulties in controlling the product quality, slow deposition rate and expensive equipments. Up to now electroplating remains the simplest and cheapest technique capable to produce homogeneous, good looking, very thin silver deposits. Unfor- tunately, almost all the electroplating baths industrially used for silver electroplating are extremely toxic due to their large cyanide content. In aqueous environments, cyanide is unavoid- able in order to complex Ag + ions avoiding their spontaneous reduction. Besides the threat to the operator's health, the disposal of the exhausted plating bath and waste water treatment, are becoming more and more expensive. Ionic liquids (ILs) are a relatively new class of compounds that have attracted intensive interest as a replacement media for a large number of applications [3,4] including electrochemical deposition of metals, due to their thermal stability, good conductivity, low toxicity and non-volatility and recyclability [3,5]. A survey of the chemical and physical properties of ILs can be found in the recent review papers [6,7], while a specific review on their electrochemical properties has been published by Galinski and coworkers [8]. The electrodeposition of metals from ILs has been intensively investigated and a review of these results has been recently published by Abbott and McKenzie [9]. The air and water-stable ILs, based on imidazolium salts, appear Surface & Coatings Technology 201 (2007) 9485 – 9490 www.elsevier.com/locate/surfcoat ⁎ Corresponding author. Tel.: +39 055 457 3119; fax: +39 055 457 3120. E-mail address: stefano.caporali@unifi.it (S. Caporali). 0257-8972/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2007.04.008