Electron transport and electrocatalytic properties of MWCNT/nickel nanocomposites: Hydrazine and diethylaminoethanethiol as analytical probes Abolanle S. Adekunle a , Kenneth I. Ozoemena a,b, * a Department of Chemistry, University of Pretoria, Pretoria 0002, South Africa b Energy and Processes Unit, Materials Science and Manufacturing, Council for Scientific and Industrial Research (CSIR), Pretoria 0001, South Africa article info Article history: Received 17 November 2009 Received in revised form 13 April 2010 Accepted 14 April 2010 Available online 20 April 2010 Keywords: Multi-walled carbon nanotube Edge plane pyrolytic graphite electrode Nickel and nickel oxide nanoparticles Cyclic voltammetry Impedance spectroscopy Hydrazine abstract This work describes the electron transport and electrocatalytic properties of chemically-synthesized nickel (Ni) and nickel oxide (NiO) nanoparticles supported on multi-walled carbon nanotubes (MWCNT) platforms. Successful modification of the electrodes with the Ni and NiO nanoparticles was confirmed by techniques such as FTIR, FESEM, HRSEM, TEM, XRD, EDX and cyclic voltammetry (CV). The electrocata- lytic oxidation of DEAET and hydrazine on the modified electrodes was investigated using CV and elec- trochemical impedance spectroscopy (EIS) and discussed. Results showed that EPPGE–MWCNT–Ni electrode gave the best electro-oxidation response towards DEAET and hydrazine. The catalytic rate con- stant and the limit of detection of the electrode to DEAET and hydrazine were 5.93  10 9 cm 3 mol 1 s 1 (0.87 lM) and 7.67  10 8 cm 3 mol 1 s 1 (0.29 lM), respectively. The electrochemical Gibbs free energy change due to adsorption (DG 0 ) for the EPPGE–MWCNT–Ni in DEAET and hydrazine were estimated as 18.14 and 17.21 kJ mol 1 , respectively. The electrode has proven to be a potential electrochemical sensor for DEAET and hydrazine. Ó 2010 Elsevier B.V. All rights reserved. 1. Introduction Metal nanoparticles as catalysts have been vigorously investi- gated because of their specific properties, such as large surface area, and their superior properties, different from those of the bulk materials [1]. Nevertheless, with the high surface area to volume ratios and surface energies, the stabilization of synthesized nano- particles becomes one of the primary challenges for some of their applications. Stabilization agents or substrates used for metal nanoparticles synthesis include: carboxylic acid [2], crown ether [3], sodium citrate [4] and carbon nanotubes (CNTs) [5–8]. Among them, CNT-stabilized nanoparticles are important due to their po- tential applications as broad-band optical emitters [5], electrodes [6] and catalysts [8]. Acid treated CNTs are composed mainly of carboxylic and phenolic groups, which can act as nucleation cen- tres for metal ions during the reduction [9]. Until now, only a few works on the preparation of mono-disperse nickel nanoparticles have been reported [10–12]. Among several applications of Ni-based species as sensor for both biological and chemical analytes include carbon composite electrode (CCE) modi- fied with nickel (II) hexacyanoferrate used for amperometric detec- tion of thiosulfate [13], modified CCE with Ru-complex and nickel pentacyanonitrosylferrate for detection of sulfur oxoanions [14], nickel electrodes and glassy carbon electrode modified with nickel film for sulphides detection in alkaline or acidic media [14]. Others include detection of thiocyanate ion [15], glucose [16], and recently, diethlaminoethanethiol (DEAET) [17]. On the other hand, NiO nano- particles have gain interests as supporting materials or catalyst for sensing purpose [18], while Ni–MWCNT modified electrode had also been used in supercapacitors [19]. Due to the electronic prop- erties of carbon nanotubes electronic properties and their large sur- face area [6], research on the possible applications of CNTs decorated with metal nanoparticles, particularly nickel is beginning to receive some attention in electrochemistry [19–24]. Hydrazine (N 2 H 4 ) is an important analyte which has found applications in the manufacture of photographic developing solu- tions, insecticides [25], agriculture chemicals, power reducing agent in fuel cells [26], corrosion inhibitor and antioxidant [25]. Hydrazine and its methyl derivatives have been implicated as po- tential carcinogens, mutagens and hepatotoxic substances that could cause liver and kidney damages [27]. These properties of hydrazine, both as useful materials and hazardous substances, have made it imperative to study its electro-oxidative behaviour at low cost and easily available carbon electrodes. The Chemical Weapons Convention (CWC) prohibits the devel- opment, production and stockpiling of chemical warfare (CW) agents and their precursors in the environment and other related matrices [28]. 2-Diethylaminoethanethiol (DEAET) is a thiol com- pound and the degradation product of the V-type nerve agent 1572-6657/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jelechem.2010.04.010 * Corresponding author at: Energy and Processes Unit, Materials Science and Manufacturing, Council for Scientific and Industrial Research (CSIR), Pretoria 0001, South Africa. Tel.: +27 12 841 3664; fax: +27 12 841 2135. E-mail address: kozoemena@csir.co.za (K.I. Ozoemena). Journal of Electroanalytical Chemistry 645 (2010) 41–49 Contents lists available at ScienceDirect Journal of Electroanalytical Chemistry journal homepage: www.elsevier.com/locate/jelechem