ISSN 1068-3755, Surface Engineering and Applied Electrochemistry, 2012, Vol. 48, No. 2, pp. 170–174. © Allerton Press, Inc., 2012. Original Russian Text © R.D. Apostolova, Yu.A. Tkachenko, O.V. Kolomoyets, E.M. Shembel’, 2012, published in Elektronnaya Obrabotka Materialov, 2012, No. 2, pp. 97–103. 170 INTRODUCTION Electrochemical capacitors (EC) are used as power sources in computing, audio, video equipment, medi- cal and household appliances, in clocks, electronic games, cameras, hybrid engine starting systems, backup power sources, and other devices. As the need for power sources of high energy, power, and increased resources is continually growing, hybrid devices that combine lithium-ion intercalation or other systems and electrochemical capacitors such as Faraday pseudocapacitors or non-Faraday double-layer capac- itors are becoming more and more attractive. In this regard, the range of studies of the modification and development of electrode materials for EC is con- stantly expanding [1–3]. The authors believe that oxides and sulfides of tran- sition metals obtained in thin layers on metal bases are promising electrode materials for thin-layer electro- lytic EC [4]. Studies of thin-layer electrolytic nickel sulfide NiS in an alkaline medium have shown that nickel sulfide is converted to a nickel oxide compound that can exhibit 147 F/g when cycling for more than 200 cycles [5]. Electrode materials based on nickel oxide compounds are of interest in regards to EC. Their characteristics depend greatly on the active mass obtaining method. Electrolytically produced compos- ites of NiO nanoscale plates at carbon nanofibers in an KOH solution (1 mol/L) provide a capacitance of 465 F/g in the range of 0–0.45 V (relative to Ag/AgCl) [6]. Composite carbon nanosized tubes with NiO in a KOH solution (2 mol/L) give 102.6 F/g [7]. The capacitor characteristics of the NiO films obtained by the hydrothermal method are inferior to the charac- teristics of the electrochemically deposited films of NiO with a capacitance of 148 F/g, which have a sim- ilar crystal structure but different a surface morphol- ogy [8]. According to [9], the capacitance of the NiO electrode reaches only 10 F/g, while, according to [10], 59 F/g, whereas the capacitance of electrodepos- ited Ni(OH) 2 reaches 2595 F/g [11]. As the continuation of previous work [5], in this report, we present the results of the study of the pseudocapacitor properties of electrolytic thin-layer nickel hydroxide Ni(OH) 2 in KOH solutions. Nickel hydroxide Ni(OH) 2 is used in electrodes (particularly in alkaline batteries) as the positive elec- trode active material, in which the following reversible reaction occurs: Ni(OH) 2 + OH – NiOOH + H 2 O + (1) The reversibility of reaction (1) is explained by the high efficiency of the redox transitions between the main phases of α-Ni(OH) 2 , β-Ni(OH) 2 , β-NiOOH, and γ-NiOOH in accordance with the scheme pro- posed by Bode et al. [12] and further supplemented in [13], while remaining a subject of controversy in stud- ies of Ni(OH) 2 . The most important characteristics are the structure and surface area, which determine the capacitor properties of Ni(OH) 2 and depend on the synthesis conditions and changes in the Ni(OH) 2 in the process of the operation and storage. Below are the results of studies of electrolytic thin- layer hydroxide Ni(OH) 2 in an alkaline medium depending on the method and technical parameters of e . Thin-layer Electrolytic Nickel Hydroxide Ni(OH) 2 in an Electrochemical Capacitor R. D. Apostolova a , Yu. A. Tkachenko a , O. V. Kolomoyets a , and E. M. Shembel’ a, b a Ukrainian State University of Chemical Technology, pr. Gagarina 8, Dnepropetrovsk, 49005 Ukraine b Enerize Corporation, Coral Springs, Fl, USA e-mail: shembel@onil.dp.ua Received July 18, 2011 Abstract—Thin-layer electrolytic nickel hydroxide Ni(OH) 2 has been obtained from an aqueous solution of nickel sulfate and nickel nitrate. The capacitor characteristics of Ni(OH) 2 depending on the synthesis and technology parameters, the thermal treatment and storage conditions of the deposits, the KOH concentra- tion, the potential sweep rates, and the relation with the adverse process of oxygen isolation in an electro- chemical capacitor were investigated by cyclic voltammetry. It was established that the optimal KOH concen- tration in the solution of an electrochemical capacitor is 0.1 M, and it allows one to attain an active material discharge capacitance of 427–457 F/g. The additional anode polarization of cathode deposited Ni(OH) 2 sta- bilizes the discharge characteristics of the obtained Ni(OH) 2 + NiO mixture in storage processes. It was established that the mass transport process in the solid state phase is the limiting stage of the Ni(OH) 2 /NiOOH system’s electrode process in a KOH medium. DOI: 10.3103/S1068375512020020