Electrochimica Acta 55 (2010) 1120–1124 Contents lists available at ScienceDirect Electrochimica Acta journal homepage: www.elsevier.com/locate/electacta Electrochemical properties and hydrogen storage mechanism of perovskite-type oxide LaFeO 3 as a negative electrode for Ni/MH batteries Gang Deng a , Yungui Chen a,∗ , Mingda Tao a , Chaoling Wu a , Xiangqian Shen a , Heng Yang a , Ming Liu b a School of Materials Science and Engineering, Sichuan University, Chengdu 610065, PR China b Analysis and Testing Center, Sichuan University, Chengdu 610064, PR China article info Article history: Received 10 June 2009 Received in revised form 28 September 2009 Accepted 28 September 2009 Available online 4 October 2009 Keywords: Hydrogen storage Perovskite-type oxide Negative electrode Ni/MH batteries abstract Perovskite-type oxide LaFeO 3 powder was prepared using a stearic acid combustion method. Its phase structure, electrochemical properties and hydrogen storage mechanism as negative electrodes for nickel/metal hydride (Ni/MH) batteries have been investigated systematically. The results of X-ray diffrac- tion (XRD) analysis show that both the calcined powder and the charged/discharged samples after 10 cycles have orthorhombic structures. The discharge capacity, whose maximum value appeared at the first cycle, is 530.3 mA h g -1 at 333 K and increases with an increase in temperature. The discharge capacity decreases distinctly during the first three cycles and then stays steady at about 80 mA h g -1 , 160 mA h g -1 and 350 mA h g -1 at 298 K, 313 K and 333 K, respectively. The hydrogen storage mechanism is studied by XRD, X-ray photoelectron spectroscopy (XPS) and mass spectrometry (MS), coupled with pressure–composition–temperature (PCT) methods. Hydrogen atoms may be intercalating into the oxide lattice and forming a homogeneous solid solution during the charging process. Crown Copyright © 2009 Published by Elsevier Ltd. All rights reserved. 1. Introduction Nickel/metal hydride (Ni/MH) batteries have been widely studied due to their high capacities, fast charge and discharge capabilities, environment-friendly characteristics and long cyclic stability [1–4]. All of the traditional negative materials in Ni/MH batteries are hydrogen storage alloys, including AB 5 [5,6], AB 2 [7], AB [8], and Mg-based materials [9–11]. Although Ni/MH secondary batteries with AB 5 -type hydrogen storage alloys as negative elec- trodes have been widely applied in portable electronic devices, hand tools and vehicles, the reversible capacities of the alloys are only about 300 mA h g -1 . Moreover, the existence of Co in com- mercial AB 5 -type electrodes increases the price a lot, which is unfavorable for electric vehicle applications, though it prevents the rapid decline in the alloy’s hydrogen absorption capability during the charge–discharge cycling. A solid material that can store hydro- gen reversibly with a capacity of 6.5 mass% and 62 kg H 2 m -3 is the ideal target recommended by the U.S. Department of Energy (DOE) for automobile applications. Therefore, great effort has been invested in developing new types of hydrogen storage materials with improved electrochemical properties at lower cost than state- of-the-art negative electrodes [12–15]. Mandal et al. [16] have ∗ Corresponding author. Tel.: +86 28 8540 7335; fax: +86 28 8546 6916. E-mail addresses: ygchen60@yahoo.com.cn (Y. Chen), Mingliu@scu.edu.cn (M. Liu). developed an unprecedented intake of hydrogen by BaMnO 3 /Pt to the extent of 1.25 mass% at moderate temperatures (190–260 ◦ C) at ambient pressure. However, little attention has been paid to the study of proton-conductive perovskite-type oxides despite their promising characteristics as negative electrode materials for Ni/MH secondary batteries. Esaka et al. [17] has proposed perovskite-type oxides ACe 1-x M x O 3-ı (A = Sr or Ba, M = rare earth element) pre- pared by a conventional solid-state reaction method as innovative electrode materials for Ni/MH batteries. They deduced that the hydrogen storage mechanism is as follows: BaCe (IV) 0.95 Nd 0.05 O 3-ı + xH 2 O + xe - charge ⇋ discharge BaCe IV 0.95-x Ce (III) x Nd 0.05 O 3-ı H (I) x + xOH - (1) Unfortunately, the maximum discharge capacity of the BaCeO 3 - based samples was only 119 mA h g -1 at the discharge current density of 9.25 mA g -1 . Up to now, further research results have not been extensively reported. Recently our research team reported that the discharge capacities of the ABO 3 -type perovskite oxide La 1-x Sr x FeO 3 were more than 500 mAh g -1 at a discharge current density of 31.25 mA g -1 when the temperature rose to 333 K [18]. ABO 3 -type perovskite oxides are superior to traditional hydrogen storage alloys because of their high hydrogen storage capacity, particularly at higher temperature, and at low cost. However, the electrochemical hydrogen storage mechanism of the perovskite oxide has yet to be elucidated. 0013-4686/$ – see front matter. Crown Copyright © 2009 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2009.09.078