Journal of Power Sources 201 (2012) 360–367 Contents lists available at SciVerse ScienceDirect Journal of Power Sources jou rnal h omepa g e: www.elsevier.com/locate/jpowsour An insight into the electrochemical behavior of Co/Al layered double hydroxide thin films prepared by electrodeposition Erika Scavetta a,∗ , Barbara Ballarin a , Claudio Corticelli a , Isacco Gualandi a , Domenica Tonelli a , Vanessa Prevot b,c , Claude Forano b,c , Christine Mousty b,c,∗∗ a Dip. Chimica Fisica e Inorganica, ALMA MATER STUDIORUM-Università di Bologna Viale Risorgimento 4, 40136 Bologna, Italy b Clermont Université, Université Blaise Pascal, Laboratoire des Matériaux Inorganiques, BP 10448, F-63000 Clermont-Ferrand, France c CNRS, UMR 6002, LMI, F-63177 Aubière, France a r t i c l e i n f o Article history: Received 5 September 2011 Accepted 31 October 2011 Available online 6 November 2011 Keywords: Co/Al layered double hydroxide Electrodeposition Coated electrode Electrooxidation a b s t r a c t A detailed study aimed at clarifying the electrochemical behavior of Co/Al-LDH thin films, prepared on Pt electrode by electrodeposition at -0.9 V, has been carried out. Reproducible thin and homogeneous films with variable amounts of LDH coated on the electrode surface have been achieved by varying the electrodeposition time (t = 5, 10, 30 and 60 s): 29.2 ± 0.7, 37.9 ± 1.4, 55.1 ± 2.1 and 62.5 ± 4.3 g cm -2 , respectively. X-ray diffraction, spectroscopic techniques and the electrochemical quartz crystal microbal- ance analysis have been used to give an insight into the phase changes occurring when the as-prepared Co/Al-LDH thin films were oxidized and reduced by cycling the potential between 0 and 0.6 V/SCE in 0.1 M KOH. Our experiments demonstrate that the irreversible oxidation peak observed in the first cycle corresponds to the transformation of the Co(II)/Al-LDH phase in a -Co(III)OOH like phase. This result- ing phase is stable under cycling and shows a pseudo-capacitive behavior with an estimated specific capacitance of 500 F g -1 . © 2011 Elsevier B.V. All rights reserved. 1. Introduction Layered double hydroxides (LDH) or hydrotalcite-like com- pounds (HTlc) are lamellar compounds with the chemical formula [M a (II) 1-x M b (III) x (OH) 2 ] x+ (A n- x/n ) × mH 2 O, shortly named M a /M b -A, where M a (II) and M b (III) are metal cations, A n- is an anion. Pure LDH phases with M a equal cobalt can be obtained with x rang- ing between 0.22 and 0.50 [1,2]. Due to their anion exchange and intercalation properties and their wide range of metal composi- tions, LDH have found many applications in different fields, such as precursors for coatings and catalysts [3,4], hosts for photoac- tivation and photocatalysis [5] and anion exchangers [6]. More recently, these materials have been also applied with increasing interest to the electrochemical field, in energy storage devices [7,8], as electrode coatings for amperometric or potentiometric sensors [9–11] and as biosensors, being suitable hosts for enzymes [12,13]. In particular, cobalt containing LDH phases have been evaluated ∗ Corresponding author. Tel.: +39 0512093256; fax: +39 0512093690. ∗∗ Corresponding author at: Clermont Université, Université Blaise Pascal, Labo- ratoire des Matériaux Inorganiques, BP 10448, F-63000 Clermont-Ferrand, France. Tel.: +33 473 407 598; fax: +33 473 407 108. E-mail addresses: erika.scavetta2@unibo.it (E. Scavetta), Christine.Mousty@univ-bpclermont.fr (C. Mousty). as amperometric sensors to detect sugars [14]. Recently, an elec- trochromic device, based on an ITO electrode coated with a thin film of electrodeposited Co/Al-LDH, has been successfully devel- oped [15]. Furthermore, Co based LDH modified electrodes, as thin films or as pressed electrodes, have been used as supercapacitors, energy storage devices that possess high energy densities and long cycle lifetimes [16–23]. Note that Co containing LDH phases can be easily prepared by coprecipitation involving the mixing of a metal salt solution and an alkaline solution [24]. However with the aim of tuning struc- tural and morphological properties of LDH, alternative synthetic methods have been described. Uniform and large-sized platelets of well-crystallized Co/Al-LDH have been synthesized by homoge- nous precipitation method based on the slow hydrolysis of urea [25]. Recently, O’Hare et al. [26] reported that the combination of homogenous precipitation and reverse microemulsion method permits to prepare Co/Al-LDH nanoplatelets with controlled parti- cle sizes. Co based LDH gels are also accessible either by a sol–gel process involving hydrolysis and condensation of alkoxides precur- sors in alcohol [27,28] or by acetate precursors hydrolysis in polyol medium [29]. Moreover, to prepare LDH thin films, a promising procedure optimized in the last few years by Scavetta et al. [30,31] consists of a one-step electrodeposition of Ni/Al or Co/Al-LDHs allowing simultaneously LDH synthesis and modification of the electrode’s 0378-7753/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2011.10.122