Applied Surface Science 283 (2013) 871–875 Contents lists available at ScienceDirect Applied Surface Science j ourna l ho me page: www.elsevier.com/locate/apsusc Cobalt hydroxide ultra-fine nanoparticles with excellent energy storage ability Mustafa Aghazadeh a,∗ , Abbas-Ali Malek Barmi a , Davoud Gharailou a , Mohammad Hassan Peyrovi b , Behrouz Sabour b , Firouzeh Najafi Khosroshahi a a Department of Chemistry, Faculty of Science, Islamic Azad University, Shahr-e-Ray Branch, Tehran, Iran b Department of Chemistry, Faculty of Science, Shahid Beheshti University, G. C., P.O. Box 19396-4716, Tehran, Iran a r t i c l e i n f o Article history: Received 14 November 2012 Received in revised form 4 July 2013 Accepted 9 July 2013 Available online 16 July 2013 Keywords: Nanoparticles -Co(OH)2 Pulse current electrodeposition Microstructure Energy storage a b s t r a c t Pulse current deposition was applied for the first time in the cathodic electrodeposition of cobalt hydrox- ide from nitrate bath and ultrafine nanoparticles of -Co(OH) 2 were prepared via this route. The crystal structure and morphology of the prepared Co(OH) 2 were analyzed by X-ray diffraction spectroscopy, scanning and transmission electron microscopes. The XRD analysis revealed that the deposited hydrox- ide has a pure brucite-like phase of Co(OH) 2 . Morphological characterization by SEM and TEM revealed that the prepared -Co(OH) 2 is composed of well-dispersed ultrafine particles with size of about 5 nm. The energy storage ability of the prepared nanoparticles was studied by means of cyclic voltammetry (CV) and galvanostatic charge–discharge tests in 1 M KOH. The nanoparticles showed an excellent energy stor- age ability, where they delivered an energy density of 0.105 Wh/g with coulombic efficiency of 91.8%. Result of this work showed that pulse current cathodic electrodeposition can be recognized as a facile route for the preparation of very fine nanoparticles of cobalt hydroxide. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Cobalt hydroxide, Co(OH) 2 , is a main raw material for lithium ion batteries and a promising candidate for supercapacitors [1,2]. It is usually used as an additive to enhance the conductivity and chargeability of Ni(OH) 2 electrodes. All of these important applica- tions are based on its excellent electrochemical performance which is markedly depended on its grain size, morphology and crystal structure [3]. It is well known that Co(OH) 2 has two polymorphs: - and -Co(OH) 2 .  phase is metastable and easily undergoes a phase transformation into the more stable  phase in strongly alkaline media. Thus, -Co(OH) 2 is often selected as an additive for the alka- line secondary batteries due to the stability in alkaline electrolytes and enhanced conductivity when charged to -CoOOH. Various methods including chemical precipitation, hydro- thermal, solvothermal and solid-state reaction have been devel- oped for the synthesis of the nanostructure of Co(OH) 2 [4–6]. Besides these methods, cathodic electrodeposition has been also applied as an attractive technique in the preparation of Co(OH) 2 nanostructures [7–11]. Kong et al. [7] carried out deposition of Co(OH) 2 on nickel foam from nitrate bath and investigated the effects of different conditions including electrodeposition time ∗ Corresponding author. Tel.: +98 21 55229204; fax: +98 21 55229204. E-mail address: mustafa.aghazadeh@gmail.com (M. Aghazadeh). and potential on the capacitance of the prepared -Co(OH) 2 thin film. Prasad et al. [8] performed galvanostatic deposition from nitrate bath and observed that electrodeposition from Co(NO 3 ) 3 at low pH, high concentration (>1 M) and low current densities (<0.3 mA cm -2 ) leads to the formation of  phase and under other deposition conditions, the better known -Co(OH) 2 is obtained. Zhou et al. [9] investigated the effects of the electrodeposition potential and temperature on the electrochemical capacitance behavior of Co(OH) 2 films and found that Co(OH) 2 reveals the best mesoporous sheet-like morphology and the excellent spe- cific capacitance of as high as 1084 F g -1 when it is deposited at -0.75 V vs. SCE at temperature of 50 ◦ C. The galvanostatic electrodeposition has been also performed from nitrate media on the stainless steel mesh and the flexible porous nanoflakes of -Co(OH) 2 have been prepared [10]. In the previous studies, we reported the high surface area leaf-like nanostructures of - Co(OH) 2 [11] and porous nanoplates of Co 3 O 4 [12] prepared by galvanostatic electrodeposition. The specific capacitances as high as 772.8 F g -1 and 393.6 F g -1 were obtained for the -Co(OH) 2 nano-leaves and Co 3 O 4 nanoplates, respectively. Recently, high surface area Co(OH) 2 nanosheets have been prepared via cathodic electrodeposition and their electrochemical performance has been investigated using cyclic voltammetry and charge–discharge tests. A specific capacitance as high as 1047.3 F g -1 was obtained in aque- ous 1 M KOH within the potential range of -0.3 to 0.5 V (vs. Ag/AgCl) 0169-4332/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apsusc.2013.07.035