Rhodium electrodeposition on pyrolytic graphite electrode: Analysis of chronoamperometric curves Oleg Brylev a,b , Lionel Roue ´ b , Daniel Be ´langer a, * a De ´partement de Chimie, Universite ´ du Que ´bec a ` Montre ´al, C.P. 8888, succursale Centre-Ville, Montre ´al, QC, Canada H3C 3P8 b INRS – Energie, Mate ´riaux et Te ´le ´communications, 1650 Blvd Lionel Boulet, C.P. 1020, Varennes, QC, Canada J3X 1S2 Received 3 November 2004; received in revised form 19 March 2005; accepted 11 April 2005 Available online 23 May 2005 Abstract The electrodeposition of metallic rhodium on pyrolytic graphite from 10 mM Na 3 RhCl 6 +0.5 M NaCl aqueous solution was investigated for the first time. From the analysis of chronoamperometric curves, the nucleation kinetics was compared for two- dimensional (2D) and three-dimensional (3D) electrodeposition processes, applying various models. Rh electrodeposition at 172 and 232 mV vs. Ag/AgCl was interpreted in terms of 3D process of progressive type which turns into instantaneous one at more negative potentials. The principal nucleation parameters (nucleation rate constant, nucleation density) are calculated by using two frequently used models for 3D nucleation and growth (Scharifker–Mostany and Mirkin–Nilov–Heerman–Tarallo), using different fitting procedures. It is shown that both models give similar results. Ó 2005 Elsevier B.V. All rights reserved. Keywords: Rhodium; Electrodeposition; Theoretical models; Nucleation and growth kinetics 1. Introduction Rhodium is a well-known noble metal, belonging to the platinum-group, which plays an important role in many industrial applications [1,2]. The study of rhodium deposits is motivated by the well-known catalytic prop- erties of the metal. In fact, rhodium is a common com- ponent of the catalysts used for the removal of nitrogen oxides, carbon monoxide, and hydrocarbons in automo- bile exhausts and it has been successfully applied for ni- trate reduction in acidic [3,4] and neutral medium [5], in groundwater [6,7], showing the highest activity among transition and coinage metals. However, the cost of Rh restrains its industrial appli- cation: hence it is of a significant interest to obtain thin Rh films. The electrodeposition is widely used for this purpose. Rhodium has been electrodeposited on poly- crystalline and single crystal gold [8–10], Pt [11], Ti [12], vitreous carbon [13,14], and carbon-fiber materials [15]. Concerning the Rh source, different Rh salts have been used, for example, (NH 4 ) 2 RhCl 6 [16], nitric acid solutions containing various complex forms of Rh(III) [15], RhCl 3 [11,17], Rh 2 (SO 4 ) 3 [14], and Na 3 RhCl 6 [8,11,13]. The last one is usually considered as the cheap- est among them and its chemistry in aqueous solutions proves to be surprisingly simple [13], hence, it is used in our investigation. The scope of this paper is to investigate Rh electrode- position on pyrolytic graphite, which is a cheap sub- strate and, for that reason, one of the most appropriate for further industrial applications (e.g. ni- trate removal from groundwater). Chronoamperometric experiments will be used to investigate in details the nucleation and growth mechanism for rhodium parti- 0022-0728/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jelechem.2005.04.006 * Corresponding author. Tel.: +1 514 987 3000x3909; fax: +1 514 987 4054. E-mail addresses: brylev@inorg.chem.msu.ru (O. Brylev), roue@ emt.inrs.ca (L. Roue ´), belanger.daniel@uqam.ca (D. Be ´langer). www.elsevier.com/locate/jelechem Journal of Electroanalytical Chemistry 581 (2005) 22–30 Journal of Electroanalytical Chemistry