A feasibility study of scaling-up the electrolytic production of carbon nanotubes in molten salts Aleksandar T. Dimitrov 1 , George Z. Chen *, Ian A. Kinloch, Derek J. Fray * Department of Material Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ, UK Received 18 July 2002; received in revised form 28 August 2002 Abstract The feasibility of scaling-up the electrolytic production of carbon nanotubes in molten salts has been investigated with the aid of electron microscopy (TEM and SEM). Using molten LiCl as the electrolyte and commercial graphite as both cathode and anode materials, carbon nanomaterials, including nanotubes, were prepared by constant voltage electrolysis. The cell was more than 20 times as large as that used in previous work. The nanotube concentration in the final product increased with cell voltage (including iR drop) from 1 vol.% at 4.0 V to 35 vol.% at 8.4 V. Under desired conditions, the charge and energy consumption for the cathode erosion was 0.28 Ah/g and 4.1 Wh/g, of which 60  /70 wt.% were for producing nanomaterials (nanotubes: /30 vol.%). When adding 1 wt.% SnCl 2 to the electrolyte, partial and fully filled nanotubes were obtained with the nanomaterials containing up to 20 wt.% Sn. Preliminary results from applying the product as the electrode in lithium ion batteries are reported. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Carbon nanotubes; Molten salts; Electrolysis; Scaling up; Electron microscopy 1. Introduction Carbon nanotubes (CNTs) are strong, stiff, and electrically conductive. They possess large aspect ratios and surface areas, and can be either multi- or single walled structures [1]. Practical uses of CNTs have become more promising in recent years, such as fillers in polymer composites, field emitters for flat panel displays, electrodes for supercapacitors and elements in nano-electronics [2  /4]. CNTs are typically produced in the gas phase, by the evaporation of pure carbon using a high-powered energy source (e.g. electric arc, laser or solar heat) or by the catalytic decomposition of gaseous hydrocarbons over a transition metal (e.g. acetylene over Fe) [5  /7]. However, in 1995, Hsu et al. discovered that CNTs could also be produced in molten LiCl by electrolysis using high purity carbon electrodes, presenting the first example of producing CNTs in a condensed phase [8]. In their experiments, the carbon cathode underwent erosion and nanometre sized pro- ducts, including multiwalled CNTs were found in the molten salt (electrolyte). Subsequently they conducted a more detailed study and concluded that for CNT production, the immersion of cathode in the electrolyte needed to be shallow ( B/3 cm), the current moderate ( B/5 A) and the voltage low ( B/5 V) [9]. The discovery of Hsu et al. stimulated further work in this laboratory under various conditions in different electrolytes (LiCl, NaCl and KCl) and, particularly, suitable CNT pre- paration temperatures for each electrolyte were estab- lished [10,11]. It was concluded that CNTs were not to form at temperatures higher than the boiling points of the alkali metals [10,11]. In 2000, Kaptay et al. reported that, on graphite cathode, the electro-deposition of Li, Na, K, Mg and Ca from the respective molten chlorides all led to the formation of CNTs, but not of Sn and Ni [12]. Hsu et al. [13] reported later that the electrolytic method could also be used to make carbon coated metal nanowires by adding a low melting temperature metal or * Corresponding authors. Tel.:  /44-1223-762965; fax:  /44-122- 3334567 E-mail addresses: gzc20@hermes.cam.ac.uk (G.Z. Chen), djf25@hermes.cam.ac.uk (D.J. Fray). 1 Academic Visitor from the Faculty of Technology and Metallurgy, Uni versity ‘St.Cyril and Methodius’, 16 Rudjer Boskovic, 1000 Skopje, R Macedonia. Electrochimica Acta 48 (2002) 91  /102 www.elsevier.com/locate/electacta 0013-4686/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII:S0013-4686(02)00595-9