Electrochimica Acta 56 (2011) 8138–8146 Contents lists available at ScienceDirect Electrochimica Acta j ourna l ho me pag e: www.elsevier.com/locate/electacta Spectroelectrochemical study of trichloroacetic acid reduction at copper electrodes in an aqueous sodium sulfate medium María Deseada Esclapez a , María Isabel Díez-García b , Verónica Sáez b , Ignacio Tudela b , Juan Manuel Pérez c , José González-García b , Pedro Bonete a,∗ a Grupo de Fotoquímica y Electroquímica de semiconductores, Departamento de Química Física e Instituto Universitario de Electroquímica, Universidad de Alicante, Ap. Correos 99, 03080 Alicante, Spain b Grupo de Nuevos Desarrollos Tecnológicos en Electroquímica: Sonoelectroquímica y Bioelectroquímica, Departamento de Química Física e Instituto Universitario de Electroquímica, Universidad de Alicante, Ap. Correos 99, 03080 Alicante, Spain c Grupo de Espectroelectroquímica, Fotoelectroquímica y Modelización, Departamento de Química Física e Instituto Universitario de Electroquímica, Universidad de Alicante, Ap. Correos 99, 03080 Alicante, Spain a r t i c l e i n f o Article history: Received 9 February 2011 Received in revised form 14 May 2011 Accepted 27 May 2011 Available online 23 July 2011 Keywords: Trichloroacetic acid Copper electrode Degradation Treatment SERS a b s t r a c t The electrochemical reduction of trichloroacetic acid (TCAA) in water has been analyzed through voltam- metric studies with a copper rotating disc electrode supported by controlled-potential bulk electrolysis and electrochemical surface-enhanced Raman spectroscopy (SERS) experiments. The influences of the mass-transport conditions and concentration were studied. It has been pointed out that the electro- chemical reduction of trichloroacetic acid takes place prior to the massive hydrogen evolution. Strong adsorption was observed on the electrode surface, and dichloroacetic acid (DCAA), monochloroacetic acid (MCAA), and chloride anions were detected as reduction products. The SERS experiments point to a secondary mechanism in which dissociative adsorption of the trichloroacetic acid gives rise to the adsorption of CO, and therefore, to the production of 1C molecules as by-products of the electrochemical reduction. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction The electrochemistry of halogenated organic compounds has routinely been focused on the study of the mechanistic details of the cleavage of the carbon–halogen bond in organic solvents [1–4], and we have found relatively little fundamental informa- tion concerning the electrocatalytic reactions of the halogenated compounds in aqueous media [5]. However, due to recently estab- lished environmental applications of electrochemical technology in the degradation of persistent and pollutant compounds in wastew- aters, the aqueous medium is once again being studied [6–10]. The results reported vary widely, and it should be highlighted that some electrode potentials used in bulk electrolyses [11] are higher than the onset for the massive hydrogen evolution; these can yield reasonable current efficiencies, and some expectation surrounding such results. Recent results [12–14] using lead, copper, and glassy car- bon as cathode materials for the electrochemical reduction of perchloroethylene, together with the availability of new ∗ Corresponding author. Tel.: +34 965903855. E-mail address: Pedro.Bonete@ua.es (P. Bonete). spectroelectrochemical [15] techniques, have motivated the rein- troduction of fundamental studies of the electroreduction of halocompounds in aqueous media, in spite of the fact that the voltammetric responses do not give rise to well-defined waves. Concerning this, we have focused on the electrochemical degra- dation of trichloroacetic acid (TCAA). The electrocatalysis of TCAA reduction in water has not received enough attention in the litera- ture. Polarographic studies in aqueous media have been carried out for haloacetics (HAAs) [16]; a totally irreversible two-electron step- wise reduction of trichloroacetic and dichloroacetic acids (DCAA) is postulated, with loss of the chloride anion at potentials of -0.8 V and -1.57 V vs. SCE, in the pH range from 4 to 10.4. The elec- troreduction was characterized by zero-order kinetics with respect to hydrogen ions for pH values greater than 6. Chlorinated car- boxylic acids have also been the subject of fundamental studies using a platinum cathode [17] in an acidic medium. The authors reported current peaks at positive potentials on the SHE scale for monochloroacetic acid (MCAA) and DCAA, but not for TCAA. The sluggish kinetics of the electroreduction of trichloroacetic acid have provoked the analysis of different approaches for overcoming this drawback. For example, surfactant-intercalated clay films were cast on pyrolytic graphite, and the electrochemical reduction was greatly catalyzed in comparison with a bare electrode [18]. Pletcher 0013-4686/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2011.05.133