Electrogeneration of hydrogen peroxide in gas diffusion electrodes: Application of iron (II) phthalocyanine as a modifier of carbon black Fernando L. Silva, Rafael M. Reis, Willyam R.P. Barros, Robson S. Rocha, Marcos R.V. Lanza ⇑ Instituto de Química de São Carlos, Universidade de São Paulo, Avenida Trabalhador São Carlense 400, São Carlos 13566-590, SP, Brazil article info Article history: Received 13 December 2013 Received in revised form 5 March 2014 Accepted 6 March 2014 Available online 15 March 2014 Keywords: Hydrogen peroxide Gas diffusion electrodes Iron (II) phthalocyanine Electrochemical reduction of oxygen abstract Hydrogen peroxide (H 2 O 2 ) is commonly produced by redox reactions involving organic compounds in organic medium, but such processes present several limitations including the need to extract and concen- trate a highly active product. Hydrogen peroxide can be generated in situ by the electrochemical reduc- tion of oxygen in aqueous medium, and the process is particularly efficient when gas diffusion electrodes (GDEs) are employed. A key challenge in the development of such electrodes is the choice of the catalytic particles. This paper describes the evaluation of iron (II) phthalocyanine as a modifier of pigment carbon black used in the construction of GDEs. After 90 min of electrolysis at constant potential, a GDE contain- ing 5% of modifier generated 240 mg L 1 of H 2 O 2 (rate constant 7 mg L 1 min 1 ; energy consumption 165 kW h kg 1 H 2 O 2 ) while the unmodified GDE produced only 175 mg L 1 of H 2 O 2 (3 mg L 1 min 1 ; 300 kW h kg 1 H 2 O 2 ) under the same experimental conditions. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction Hydrogen peroxide (H 2 O 2 ) is a potent oxidizing agent and is used widely in organic synthesis, in bleaching paper and in the treatment of effluents containing organic contaminants [1–8]. Hydrogen peroxide may be synthesized on an industrial scale by a process involving autoxidation of a substituted anthrahydroqui- none in organic medium, followed by reduction of the anthraqui- none so-formed by hydrogen gas in the presence of a catalyst. While the anthraquinone method accounts for approximately 85% of commercially produced H 2 O 2 [9], the process is subject to a number of restrictions since it involves extraction of the organic phase followed by concentration and purification of the active agent. A number of alternative methods for the industrial synthesis of H 2 O 2 have been proposed, such as direct synthesis from molec- ular O 2 catalyzed by Au/Ti [10] or Pd/Au [11] and the application of microbial fuel cells [12]. However, these methods suffer from var- ious limitations including poor production efficiencies, elevated costs and low concentrations of H 2 O 2 formed. Furthermore, manu- facture of H 2 O 2 at a site that is distant from its point of use neces- sitates the storage and transportation of a somewhat unstable and highly active agent [9,13,14]. In this context, electrochemical technology offers the possibil- ity of generating H 2 O 2 in situ, in aqueous medium at a range of temperatures and pH values, and at concentrations reaching up to hundreds of milligrams per liter [15–21]. The primary reactant in the electrochemical process is O 2 and this should be dissolved in the reaction medium [22]. The rate of the electrochemical process depends on the efficient replacement of O 2 in the electro- lyte present at the electrode surface. However, the solubility of O 2 in water is low and decreases with increasing temperature of the medium, a factor that determines the operational limit for the synthesis of high concentrations of H 2 O 2 when conventional elec- trodes are employed. On the other hand, gas diffusion electrodes (GDEs) comprise a porous and hydrophobic structure that enables O 2 to be supplied directly to the electrode/electrolyte interface without limit [23–27]. In this manner, the GDE removes the limita- tions of mass transportation imposed by the low solubility of O 2 [27], and allows high yields of H 2 O 2 to be generated in both acidic [28] and alkaline [29] media. A key challenge in developing GDEs specifically for the genera- tion of H 2 O 2 is the choice of catalytic particles. Typically, GDEs are constructed with pigment carbon black, the particles of which have a graphite-type crystalline structure. In order to maximize the effi- ciency of H 2 O 2 generation and to achieve higher concentrations of the peroxide, particularly at less negative potentials, it is necessary to incorporate modifiers into the graphitic material. Studies have been conducted with various types of modifiers including organic [25] and organometallic [24] compounds and rare earth oxide nano- particles [26]. Such investigations are particularly important since the results obtained can provide an indication of the mechanism http://dx.doi.org/10.1016/j.jelechem.2014.03.007 1572-6657/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel.: +55 16 33738659; fax: +55 16 33739903. E-mail address: marcoslanza@iqsc.usp.br (M.R.V. Lanza). Journal of Electroanalytical Chemistry 722-723 (2014) 32–37 Contents lists available at ScienceDirect Journal of Electroanalytical Chemistry journal homepage: www.elsevier.com/locate/jelechem