ORIGINAL PAPER Synthesis of face centered cubic and hexagonal closed packed nickel using ionic liquids Abhishek Lahiri • Rupak Das Received: 5 January 2010 / Accepted: 18 July 2010 / Published online: 30 July 2010 Ó Springer Science+Business Media B.V. 2010 Abstract Nickel was electrodeposited from NiCl 2 -1- ethyl-3-methylimidazolium chloride at various tempera- tures at a constant potential. It was observed that by varying the electrolysis temperature, face centered cubic (FCC) and hexagonal close packed structured (HCP) nickel could be produced. From spectroscopic studies, it could be said that H ? ions played an important role in the formation of HCP nickel. The hydrogen content in HCP nickel was found to be 1.2 wt%. From the Chronoamperometric studies, the diffusion coefficient of the electroactive species for the electrodeposition of nickel at 150 °C was estimated to be 1.1 9 10 -5 cm 2 s -1 . Keywords Nickel  Hydrogen storage  Electrodeposition  Ionic liquids  Diffusion coefficient 1 Introduction Nickel has two crystal structures namely, the stable face centered cubic (FCC) and hexagonal close packed (HCP). However, the HCP nickel is considered to be metastable phase [1, 2]. The nickel hydrogen phase diagram shows that at high pressures of greater than 100 Mpa there is considerable solubility of hydrogen [3, 4]. At extremely high pressure of 1600–1900 Mpa, nickel forms a low hydrogen content a-Ni solid solution and a hydrogen rich nonstoichiometric b-Ni hydride phase [3]. Such high hydrogen fugacity can be achieved by electrochemical deposition. FCC nickel is usually formed by reducing nickel oxide by hydrogen at high temperature [5]. On contrary, the formation of HCP nickel involves complicated steps. There are few literatures available on the synthesis of HCP nickel. Carturan et al. [6] synthesized HCP nickel by reacting Ni(II) complexes with K/B liquid alloy at 200 °C whereas Mi et al. [7] used NiCl 2 and reacted it with KBH 4 and ethelenediamine at temperatures ranging from 200 to 400 °C. It was also shown that HCP nickel can be obtained by sputtering nickel in hydrogen atmosphere [8]. However, pure HCP nickel phase could not be achieved by the sputtering technique. As HCP nickel is metastable and can be formed in presence of hydrogen, we electrochemically synthesized HCP nickel from NiCl 2 -1-ethyl-3-methylimidazolium chloride. It was observed that FCC nickel formed at 140 °C whereas HCP nickel could be formed at 160 °C. To understand the reaction mechanism for the electro- deposition of nickel, the electrolyte was analyzed using Fourier Transform Infrared Spectroscopy (FTIR). Electro- chemical studies were also performed using chronoamp- erometric technique. To identify the phases formed at the cathode, the material was characterized using scanning electron microscopy (SEM), Energy dispersive X-ray (EDX) and X-ray diffraction (XRD) technique. 2 Experimental Ionic liquid of 1-ethyl-3-methylimidazolium chloride tita- nium metal and NiCl 2 were obtained from Sigma-Aldrich. 5.4 mol% of NiCl 2 was dissolved into EmimCl in a Pyrex A. Lahiri  R. Das Department of Metallurgy and Materials Engineering, University of Alabama, Tuscaloosa, AL 35487, USA A. Lahiri (&) WPI AIMR, Tohoku University, Sendai 980-8579, Japan e-mail: lahiri.abhishek@gmail.com 123 J Appl Electrochem (2010) 40:1991–1995 DOI 10.1007/s10800-010-0178-7