Available online at www.sciencedirect.com Electrochimica Acta 53 (2008) 7426–7435 Electrodeposition of iron in sulphate solutions S.L. D´ ıaz a,1 , J.A. Calder ´ on c,1 , O.E. Barcia a,b,1 , O.R. Mattos a,∗,1 a LNDC—Laborat´ orio de Ensaios N ˜ ao-Destrutivos e Corros˜ ao Prof. Manoel de Castro, EE/PEMM/COPPE, Universidade Federal do Rio de Janeiro, UFRJ, Cx. Postal 68505, CEP 21945-970, Rio de Janeiro, RJ, Brazil b Dep. F´ ısico-Qu´ ımica, IQ/UFRJ, Rio de Janeiro, RJ, Brazil c Grupo de Corrosi´ on y Protecci´ on, Universidad de Antioquia, Medell´ ın, Colombia Received 18 July 2007; received in revised form 8 January 2008; accepted 8 January 2008 Available online 17 January 2008 Abstract The kinetics of iron electrodeposition from acid sulphate solutions onto a platinum electrode was investigated by means of stationary polarisation curves and electrochemical impedance spectroscopy. Together with interfacial pH data previously obtained, the effect of pH was analysed. The formation of at least three adsorbed intermediates at the cathode surface was evidenced in all pH values. The relative rate of their formation and its surface concentration depend on the solution pH as well as on the electrode potential. It is suggested that two of these species catalyses the H + reduction whereas the other one may have a blocking effect on this reaction. © 2008 Elsevier Ltd. All rights reserved. Keywords: Fe electrodeposition; Adsorbed intermediates; Impedance; pH effects; Mechanism 1. Introduction Investigations on iron electrodeposition have been basi- cally restricted to the effects of deposition parameters on the morphological, structural and magnetic properties of the deposits [1–3]. Moreover, the fundamentals of the mechanism that governs iron electrodeposition have received less atten- tion if compared to the highly investigated Fe alloy systems. Indeed, the nature of the anomalous electrodeposition of Fe alloys, such as Zn–Fe, Co–Fe and Ni–Fe, has been the sub- ject of many researches [4–6] but the mechanisms still require improvements. In this particular case, to better understand the codeposition processes, the knowledge on the individual deposition mechanisms must be established. In addition, the increasing interest on the development of Fe thin deposits for magnetic applications [3,7] also calls for the comprehension of the elementary steps that take place during the electrodeposi- tion. Kabanov et al. [8], Bonh¨ oeffer and Jena [9] and later Bock- ris et al. [10] were the earliest to mention the formation and ∗ Corresponding author. Tel.: +55 21 2562 8550; fax: +55 21 2290 1544. E-mail addresses: susana@metalmat.ufrj.br (S.L. D´ ıaz), omattos@metalmat.ufrj.br (O.R. Mattos). 1 ISE member. participation of Fe hydroxide species during iron electrodisso- lution/electrodeposition. Some other more recent works [11,12] have also considered the contribution of this species that result from the increase on the pH of the solution adjacent to the cathode. The presence of this species at the electrode/solution interface might generate adsorption/desorption processes. By investigating Fe nucleation kinetics on a vitreous carbon elec- trode through electrochemical techniques and AFM microscopy, Grujicic and Pesic [13] proposed a theoretical model for Fe elec- trodeposition based on a progressive nucleation mechanism that was associated with the degree of inhibition of the nucleation sites. Evidences of surface alkalination during Fe-group metal and their alloy electrodeposition have been found by means of pH measurements at the vicinity of the electrode using different techniques [14,15]. In a previous work [16], interfacial pH measurements were performed during Zn–Fe electrodeposition using an in-situ non-intrusive setup. It was verified that the interfacial pH increases during individual Fe electrodeposition, meaning that it occurs with simultaneous H + consumption. Electrochemical impedance technique provides information on electrodeposition processes by means of time constants asso- ciated with the elementary steps of these systems. Epelboin et al. [17] indicated that the charge transfer in multiple steps might take place at the electrode surface through adsorbed 0013-4686/$ – see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2008.01.015