Direct synthesis of Ni 2 Al(OH) 7 À x (NO 3 ) x Á nH 2 O layered double hydroxide nanolayers by SILD and their capacitive performance V.P. Tolstoy, A.A. Lobinsky n , O.V. Levin, L.I. Kuklo Department of Chemistry, Saint-Petersburg State University, Peterhof, 198504 Saint-Petersburg, Russian Federation article info Article history: Received 9 September 2014 Accepted 28 September 2014 Available online 12 October 2014 Keywords: Layered double hydroxide Aqueous battery SILD Nanolayers abstract New method of synthesis of Ni 2 Al(OH) 7 Àx (NO 3 ) x Á nH 2 O layered double hydroxide (LDH) films by SILD (Successive Ionic Layer Deposition) is presented in this paper. The obtained nanolayers were character- ized by SEM, XRD, FTIR spectroscopy and electrochemical techniques. The results showed that the as-synthesized product is formed by nanoparticles not greater than 20–100 nm in diameter, having hydrotalcite crystal structure. Electrochemical characterization of the sample prepared by 50 cycles of SILD indicated a capacitive behavior with the specific capacitance value of 52.8 mA h/g at a current density of 1 A/g and 72.2 mA h/g of 0.5 A/g in 1 mol/L KOH aqueous solution. The presented convenient route of synthesis may be used for the preparation of LDH films with high surface area and a large capacitance. & 2014 Elsevier B.V. All rights reserved. 1. Introduction LDH belongs to a numerous group of materials composed of positively charged octahedral sheets with common formula [M 1 Àx 2 þ M x 3 þ (OH) y ], where M 2 þ can be, for example, Ni 2 þ and M 3 þ –Al 3 þ separated by exchangeable anions, including CO 3 2 À or NO 3 À , and water molecules [1]. They are widely used as effective ion- exchange materials, sorbents, materials for optical or magnetic applications, catalysts, electrodes for aqueous battery, etc. [2]. Techniques of LDH synthesis are described in reviews [3,4], one can emphasize sedimentation, sol–gel, ion-exchange and hydro- thermal techniques. Thin layers of LDH are obtained by spin- coating [5] and salts hydrolysis on the solution-ammonia phase boundary [6]. New possibilities of layered LDH synthesis rose after development of Layer-by-Layer (LbL) synthesis techniques that makes possible to deposit LDH layers on the surface of samples with irregular shape, providing exact thickness of the layer [7,8]. In paper [9] as reagents for the LbL synthesis has been used colloid solutions of LDH and solutions of polyelectrolytes. In this study, we on the example of Ni 2 Al(OH) 7Àx (NO 3 ) x Á nH 2 O describe a new simple route of LDH nanolayers SILD synthesis from solutions of nickel and aluminum salts, and its application to aqueous battery electrode materials. This method is one of methods for the LbL synthesis, and has previously been used for the synthesis of a nanolayers of oxides, peroxides, metal fluorides, etc. [10]. 2. Experimental As a substrate for nanolayers synthesis 5 Â 25 mm polycrystalline nickel foam (NF) plates (110 PPI) were used, on which electroche- mical experiments were preformed, and also 10 Â 25 Â 0.35 mm single-crystal silicon plates with 〈100〉 orientation, were used for physical characterization. Extra pure water (Mili-Q) was used in all experiments. Substrates were cleaned in an ultrasonic bath filled with acetone for 10 min. Than silicon plates were sequentially treated for 10 min in concentrated HF, water, 70% HNO 3 , water, 0.1 M KOH and than flushed out by water. NF plates were treated according to the technique described in [11] for 15 min in 6 М HCl solution, then several times rinsed by water and dried on air at 120 1C for 30 min. Aqueous 0.01 M solutions of analytical grade Ni(NO 3 ) 2 Á 6H 2 O (pH 6.5) and Al(NO 3 ) 3 Á 9H 2 O (pH 9.5) were used. рН of these solutions was controlled by addition of NaOH solution. For synthesis of LDH substrate plates were sequential immersed for 30 s into solution of nickel salt, water, solution of aluminum salt and again water. The sequence corresponds to one SILD cycle, which is repeated 50 times to obtain the desired film thickness. FTIR transmission spectra of synthesized films on silicon sur- face were registered by Shimadzu IR Prestige-21 spectrophot- ometer using differential technique with respect to spectra of bare silicon plate. Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/matlet Materials Letters http://dx.doi.org/10.1016/j.matlet.2014.09.134 0167-577X/& 2014 Elsevier B.V. All rights reserved. n Corresponding author. Tel.: þ7 8124284104. E-mail addresses: vptol@yandex.ru (V.P. Tolstoy), lobinsky.a@gmail.com (A.A. Lobinsky), levin@chem.spbu.ru (O.V. Levin), lenkuklo@mail.ru (L.I. Kuklo). Materials Letters 139 (2015) 4–6