Electrochimica Acta 70 (2012) 153–157 Contents lists available at SciVerse ScienceDirect Electrochimica Acta jou rn al hom epa ge: www.elsevier.com/locate/electacta Electrocatalysis of free glycerol at a nanonickel modified graphite electrode and its determination in biodiesel Ramin M.A. Tehrani a , Sulaiman Ab Ghani b,∗ a Department of Chemistry, Shahre Rey Branch, Islamic Azad University, Tehran, Iran b Pusat Pengajian Sains Kimia, Universiti Sains Malaysia, 11800 USM, Pulau Pinang, Malaysia a r t i c l e i n f o Article history: Received 4 November 2011 Received in revised form 8 March 2012 Accepted 10 March 2012 Available online 17 March 2012 Keywords: Biodiesel Electrocatalytic oxidation Glycerol Hexagonal close-packed Nickel nanocrystals a b s t r a c t This study reports the success of using an electrosynthesized nanocrystalline hexagonal close-packed (hcp) nickel (Ni) modified composite graphite (CG) electrode for the electrocatalytic oxidation of glycerol in alkaline medium (0.1 M KOH). The hcp-nano Ni modified CG had an improved response and remarkable electrocatalytic oxidation of glycerol over the bare CG. The electrocatalysis was the result of the formation of NiOOH during the oxidation process. The process was influenced by the scan rate and concentration of glycerol. A linear relationship between the concentrations of glycerol with the current was obtained over a range of 0.5–12.0 mM glycerol, with a limit of detection (S/N = 3) at 0.033 mM glycerol. The hcp-nano Ni modified CG electrode was applied to directly determine the free glycerol concentration in the biodiesel samples. As a glycerol sensor, the hcp-nano Ni modified CG is quite stable. © 2012 Elsevier Ltd. All rights reserved. 1. Introduction As fossil fuels and other energy sources are often only available in limited amount, it is important to find renewable alternatives such as biodiesel (mono alkyl esters). Biodiesel with long chain fatty acids is generated from vegetable oils and animal fats with a by-product called glycerol (the simplest triol) [1,2]. Glycerol has a high energy density, is less toxic than methanol and can be elec- trochemically oxidized. The electro-oxidation of glycerol on direct alcohol fuel cells (DAFCs) has attracted increasing attention from both energy and environmental fraternities in recent years [3,4]. The electrocatalytic oxidation of glycerol on electrodes such as pal- ladium (Pd) [1,3,4] and platinum (Pt) [2,5,6] has been investigated. However, many efforts have been undertaken to reduce the cost of production of DAFCs with the usage of less expensive electrodes such as Ni, which have an equally high catalytic activity [7–11]. The catalytic behavior of Ni toward alcohols has been investigated since the early 1970s [8]. The catalytic oxidation of alcohols is, generally, more facile in the alkaline medium [9,10] in which Ni has demon- strated long-term stability [9]. The catalytic activity is attributed to anodic polarization of the highly valent oxy-hydroxide species of Ni (i.e.,  and -NiOOH), which act as strong oxidizing agents for alcohols [8,11]. The use of Ni nanoparticles (NPs) (size 350 nm) with catalytic properties for the electro-oxidation of glycerol in alkaline media ∗ Corresponding author. Tel.: +60 46534030; fax: +60 46574854. E-mail addresses: rmt@iausr.ac.ir (R. M.A. Tehrani), sag@usm.my (S. Ab Ghani). has been reported [8]. Ni NPs normally crystallize in a face cen- tered cubic (fcc) arrangement [11,12]. However, the chemically synthesized metastable hcp Ni NPs (size ∼ 200 nm) have been utilized recently for glycerol oxidation [12]. Previously, our labo- ratory has succeeded in carrying out the electrosynthesis of hcp Ni (size ∼ 10 nm) on CG electrode via a high scan rate voltammetry technique [11]. It is the most recent report on the electrochemical synthesis of hcp Ni besides the last one reported 46 years ago [13]. The electrosynthesized hcp Ni nanocrystal has been used for the electro-oxidation of methanol in alkaline medium [9]. Glycerol is widely used as a raw material in pharmaceutical for- mulation, as a sweetener in the food industry and is a byproduct in the production of biodiesel. Thus, the quality of these materi- als must be assessed and ensured free of glycerol [2,5,14,15]. The analysis of glycerol in biodiesel has utilized chromatographic [16], photometric [17] and amperometric [14,15] methods. However, there has never been a report on the usage of hcp-nano Ni modified CG being used in the analysis of glycerol via its electro-oxidation in alkaline media. This study demonstrates the application of hcp-nano Ni modified CG electrode (hcp-nano Ni/CG) in electro- catalyzing the oxidation of glycerol and its application for direct determination of free glycerol in biodiesel samples. 2. Experimental 2.1. Reagents and apparatus All reagents (AR grade) were purchased from Fluka Chemie, Switzerland without further purification. Biodiesel (B100) samples 0013-4686/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2012.03.044