Electrochimica Acta 139 (2014) 180–189 Contents lists available at ScienceDirect Electrochimica Acta j our na l ho me pa g e: www.elsevier.com/locate/electacta Influence of the nature of the electrode material and process variables on the kinetics of the chlorine evolution reaction. The case of IrO 2 -based electrocatalysts Davide Rosestolato ∗ , Jacopo Fregoni, Sergio Ferro, Achille De Battisti Dipartimento di Scienze Chimiche e Farmaceutiche, Università degli Studi di Ferrara, via Fossato di Mortara 17, 44121, Ferrara, Italy a r t i c l e i n f o Article history: Received 27 March 2014 Received in revised form 1 July 2014 Accepted 2 July 2014 Available online 17 July 2014 Keywords: Chlorine Evolution Reaction iridium oxide adsorbed intermediates kinetics adsorption isotherm a b s t r a c t Kinetic studies on the chlorine evolution reaction (ChlER) on oxide-based materials have been the sub- ject of a number of papers since the seventies, following the introduction of DSAs (Dimensionally Stable Anodes) in chlor-alkali plants. On the basis of experimental data, different pathways have been proposed for the reaction over the years. Actually, specific experimental conditions and different approaches in sample preparation may lead to conflicting explanations. In the present paper, the ChlER kinetics has been studied at four electrode materials based on iridium and titanium oxides (with a 1:2 molar ratio). Electrodes were synthetized at two temperatures (350 and 450 ◦ C) and by two different preparation methods: physical vapor deposition (rf-magnetron sputtering) and a conventional sol-gel technique, using special precursors developed in our laboratory. Both methodologies guarantee a high level of repro- ducibility. As also observed by other authors, experimental data have shown a lack of linearity in Tafel plots, high b slopes and reaction orders with respect to chloride ≤ 1, which have been justified on the basis of a Volmer-Heyrovsky pathway, by considering a model proposed by Tilak and Conway in 1992. This approach highlighted the role of the adsorbed intermediates, also at low overpotentials, for all electrode materials. To analyze further the kinetics, Langmuir and Frumkin models for intermediates adsorption were considered. Values for the lateral interaction parameter g were estimated, which ranged between 1 and 10, in all cases. Concerning the effect of pH, its influence on the ChlER rate seems to be related only with electrode surface modifications, without any involvement of protons in the rate determining step of the process. A slight inhibiting effect was assessed, by increasing the protons concentration. Eventually, impedance spectroscopy analysis did not appear sensitive to intermediate adsorption, plausibly because of the low variation of the coverage within the Tafel region; a poorly resolved contribution related to porosity was found in the case of samples prepared at 350 ◦ C. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction The introduction of mixed-oxide film-electrodes (the so-called DSAs, Dimensionally Stable Anodes) in the chlor-alkali technology has represented a fundamental progress in industrial electrochem- istry, leading to enormous energy saving and cleaner processes, through a continuous progress in cell and electrode engineering. The impressive industrial impact of the original invention [1–5], further enhanced by the extension of DSA applications to the oxy- gen evolution reaction (relevant to aqueous electrometallurgy and hydrogen production), has obviously prompted the fundamental ∗ Corresponding author. Tel.: +39 0532 455166. E-mail addresses: rssdvd@unife.it, davide.rosestolato@gmail.com (D. Rosestolato). research, mainly addressed to DSA-coating synthesis and charac- terization. In fact, papers have been published on the subject as early as 1972-1974, already quite well focused on preparation technique and microstructural properties of RuO 2 coatings [6,7]. The further development of research has been more and more concerned with the latter themes, while what could have been the main target, the chlorine evolution reaction (ChlER), has been relatively less studied. On the other hand, the first of the two themes is quite rich and com- plex. The methodology of preparation of active coatings, with the wide variety of parameters involved (i.e., the quality and quantity of precursors, the choice of the path leading from precursor mix- ture to final mixed-oxide coating), has attracted, and attracts so far, a number of research works. In comparison, the study of a “facile” electrochemical reaction, namely the electrochemical oxidation of chlorides, has been considered a bit obvious. http://dx.doi.org/10.1016/j.electacta.2014.07.037 0013-4686/© 2014 Elsevier Ltd. All rights reserved.