Flowerlike Co 3 O 4 microspheres loaded with copper nanoparticle as an efficient bifunctional catalyst for lithium–air batteries Wei Yang a, b, c , Jason Salim d , Chao Ma a , Zhaohui Ma a, b, c , Chunwen Sun a, b, c, ⁎, Jianqi Li a , Liquan Chen a, b, c , Youngsik Kim d, ⁎⁎ a Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China b Key Laboratory for Renewable Energy, Chinese Academy of Sciences, Beijing 100190, China c Beijing Key Laboratory for New Energy Materials and Devices, Beijing 100190, China d Richard G. Lugar Center for Renewable Energy, Department of Mechanical Engineering, Indiana University Purdue University Indianapolis, Indiana 46202, United States abstract article info Article history: Received 30 October 2012 Received in revised form 5 December 2012 Accepted 5 December 2012 Available online 13 December 2012 Keywords: Porous Co3O4 microspheres Copper nanoparticles Efficient bifunctional catalyst Lithium–air batteries Hybrid electrolyte Porous flowerlike Co 3 O 4 microspheres/Cu nanoparticles composite has been synthesized via a combined solvothermal method, subsequent thermal treatment and polyol process. Due to the 3D mesoporous structure, the resulting Co 3 O 4 microspheres/Cu catalyst shows an efficient and stable bifunctional catalytic activity. The cobalt oxide-based catalysts show better performance during the discharging and charging processes at a current density of 0.05 mA cm -2 compared with that of the Vulcan XC-72. The cell with this novel catalyst can be revers- ibly charged/discharged and has a good cycle performance. The preliminary results indicate that the Porous flowerlike Co 3 O 4 microspheres/Cu nanoparticles composite is a promising material for a metal/air battery or a PEM fuel cell as an efficient and stable bifunctional catalyst. © 2012 Elsevier B.V. All rights reserved. 1. Introduction The high cost of energy storage and conversion devices such as the proton-exchange-membrane (PEM) fuel cells and metal/air batteries restrains their practical use [1,2]. Among various metal/air batteries, lithium–air batteries possess the highest theoretical gravimetric ener- gy density. However, for rechargeable lithium–air battery, another issue that has to be addressed in the current technology is the limita- tions of oxygen reduction reaction (ORR) during discharging process and oxygen evolution reaction (OER) during charging process. The sluggish kinetics of ORR and OER in lithium–air batteries are ascribed to the low efficiency of catalysts [3]. The performance of Li–air batte- ries can be drastically improved by incorporating an efficient catalyst to achieve higher discharge voltage, lower charge voltage and rate performance [4]. Therefore, the design of a low-cost and stable bi- functional electrocatalyst is a major challenge to the construction of efficient Li–air batteries. Many spinel cobaltite oxides have been investigated as electro- catalysts for the oxygen reduction reaction (ORR) or oxygen evolu- tion reaction (OER) [5,6]. Molecular mechanisms involving O 2 /H 2 O cycles at cobalt centers suggest the involvement of Co 2+ , Co 3+ , and likely Co 4+ oxidation states during catalysis [7]. In an oxygen-atom li- gand field, Co 2+ (t 2g 5 e g 2 ) is a high spin ion and substitutionally labile, whereas Co 3+ (t 2g 6 e g 0 ) with a higher oxidation state is low spin and substitutionally inert [8]. In general, the ORR is postulated to take place at active sites associated with the cations at the oxide surface in a higher oxidation state [6]. Bruce et al. reported a screening of many catalysts that could be used in facilitating the electrochemical properties of the O 2 electrode in a non-aqueous Li/O 2 cell [2]. Among the oxide catalysts studied, Co 3 O 4 gives the best compromise between initial capacity and capac- ity retention as well as the lowest charging voltage of 4 V. Dai et al. reported a hybrid material consisting of Co 3 O 4 nanocrystals grown on reduced graphene oxide as a high-performance bi-functional cata- lyst for the ORR and OER [9]. Recently, we demonstrated perovskite Sr 0.95 Ce 0.05 CoO 3 -δ loaded with copper nanoparticles on their surface are shown to be excellent, low-cost, and stable bifunctional catalysts for oxygen-reduction and oxygen-evolution reactions in aqueous solution [10]. Very recently, Xu et al. demonstrated that the ORR catalytic activity of the prepared Co 3 O 4 -based catalysts are sensitive to the number and activity of surface-exposed Co 3+ ions that can be tailored by the morphology of cobalt oxides [6]. Porous Co 3 O 4 micro- spheres with an open mesoporous structure have more exposed Co 3+ species and can increase dispersion of another active component [11]. In this work, we examine and compare the ORR and OER activities of porous Co 3 O 4 microspheres and compare with the Vulcan XC-72 and the 50% Pt/carbon-black catalysts. To further improve the catalytic Electrochemistry Communications 28 (2013) 13–16 ⁎ Corresponding author. Tel.: +86 10 82649901; fax: +86 10 82649046. ⁎⁎ Corresponding author. Tel.: +1 317 274 9711; fax: +1 317 274 9744. E-mail addresses: csun@iphy.ac.cn (C. Sun), yk35@iupui.edu (Y. Kim). 1388-2481/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.elecom.2012.12.007 Contents lists available at SciVerse ScienceDirect Electrochemistry Communications journal homepage: www.elsevier.com/locate/elecom