Electrochimica Acta 90 (2013) 332–343 Contents lists available at SciVerse ScienceDirect Electrochimica Acta jou rn al h om epa ge: www.elsevier.com/locate/electacta Electrochemical impedance spectroscopy study of the oxygen evolution reaction on a gas-evolving anode composed of lead dioxide microﬁbers Fabiano R. Costa, Débora V. Franco, Leonardo M. Da Silva ∗,1 Departamento de Química, Universidade Federal dos Vales do Jequitinhonha e Mucuri, Rodovia MGT 367, km 583, 5000, Alto da Jacuba, 39.100-000 Diamantina, MG, Brazil a r t i c l e i n f o Article history: Received 17 October 2012 Received in revised form 7 December 2012 Accepted 11 December 2012 Available online 19 December 2012 Keywords: Gas-evolving anode Lead dioxide microﬁbers Oxygen evolution reaction Adsorption of reaction intermediates a b s t r a c t The oxygen evolution reaction (OER) during the electrolysis of electrolyte-free water on a gas-evolving anode composed of lead dioxide microﬁbers (MF--PbO 2 ) was studied in a solid polymer electrolyte cell using the electrochemical impedance spectroscopy (EIS) technique. EIS spectra were recorded as a func- tion of the overpotential for the OER. Impedance spectra characterized by two time constants distributed in the low and high frequency domains indicated that both the charge transfer and adsorption of reaction intermediates affect the electrode kinetics. In addition, it was veriﬁed that morphological aspects do not comprise the main cause for the time constant observed in the high frequency domain. In trying to inter- pret the EIS ﬁndings, a transfer function was derived for the electrode mechanism of Pavlov and Monahov in order to permit the evaluation of the adsorption pseudocapacitance, the double-layer capacitance and the charge transfer and adsorption resistances. It was veriﬁed that the adsorption pseudocapacitance is potential-dependent while the double-layer capacitance is almost potential-independent. It was also ver- iﬁed that the adsorption resistance decreases exponentially upon increasing the overpotential, exhibiting Tafel-like behavior. The apparent charge transfer coefﬁcient, the exchange current density and the kinetic rate constant were evaluated from the impedance data. © 2012 Elsevier Ltd. All rights reserved. 1. Introduction The development of gas-evolving electrodes (GEE) for appli- cations in solid polymer electrolyte (SPE) reactors (cells) has permitted carrying out the electrolysis of electrolyte-free water in order to generate oxygen, oxygen-ozone and hydrogen, as well performing electro-organic synthesis and combustion (oxida- tion) of different organic pollutants [1–13]. In addition, in some cases, it is known that a given electrode material presenting some degree of instability in acid and/or alkaline environments can present very high stability when it is used as a GEE in an SPE cell [4,8,9]. In an SPE cell in the zero-gap conﬁguration, the electrode maintains intimate contact with the SPE in order to permit ionic and electronic transport inside the cell, i.e., in the reaction zones formed at the electrode/SPE/H 2 O (three-phase) interface. A very promising application of GEE in SPE cells is the electrochemical combustion of emerging pollutants found in contaminated waters as a consequence of anthropic activities (e.g., some classes of pharmaceuticals) [14]. As previously dis- ∗ Corresponding author. Tel.: +55 38 3532 6000; fax: +55 38 3532 6000. E-mail addresses: lsilvamorais@hotmail.com, leonardo.morais@ufvjm.edu.br (L.M. Da Silva). 1 ISE Member. cussed by Houk et al. [13], a distinct advantage of using SPE cell technology in large-scale applications aiming toward the combustion of pollutants is the production of a ﬁnal product (efﬂuent) without the need for desalting and/or pH adjust- ment. However, the use of SPE cells for treating pollutants present in contaminated waters has some disadvantages, such as the exces- sively long periods required for decontamination due to the low ionic strength and/or inadequate (ill-deﬁned) conﬁguration of the membrane electrode assembly [13]. Therefore, the improvement of GEEs for applications in SPE reactors aiming at the electrochemi- cal combustion of pollutants comprises an important task from the technological point of view. Suitable electrode materials for the fabrication of GEEs for applications regarding the oxidation of organic pollutants are - PbO 2 , SnO 2 –Sb 2 O 5 , BDD (boron-doped diamond), etc. [15–19]. The highest oxidation power for the combustion of pollutants is pre- sented by PbO 2 , SnO 2 –Sb 2 O 5 and BDD [20]. Despite their high efﬁciency for removing organic pollutants, doped-SnO 2 anodes have the major drawback of a short service life at moderate and high current densities that limits their practical applications [20]. As discussed by Sirés et al. [21], PbO 2 is widely used as an anode owing to its well-proven advantages, including its low cost com- pared to noble metals, ease of preparation on different substrates (planar or porous), low electrical resistivity, good chemical stability 0013-4686/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.electacta.2012.12.043