Graphene nanoplatelets supported metal nanoparticles for electrochemical oxidation of hydrazine Qijin Wan a, ⁎, Yi Liu a , Zhaohao Wang a , Wei Wei a , Beibei Li a , Jing Zou a , Nianjun Yang b, ⁎⁎ a School of Chemical Engineering & Pharmacy, Key Laboratory for Green Chemical Process of Ministry of Education, Hubei Key Lab of Novel Reactor & Green Chemical Technology, Wuhan Institute of Technology, Wuhan 430073, China b Fraunhofer Institute for Applied Solid State Physics (IAF), Freiburg 79108, Germany abstract article info Article history: Received 9 December 2012 Received in revised form 10 January 2013 Accepted 11 January 2013 Available online 20 January 2013 Keywords: Graphene nanoplatelets (GNPs) Metal nanoparticles Electrochemical oxidation of hydrazine Electrodeposition Graphene nanoplatelets have been applied as the support to electrodeposit monometallic Au and Pd nanoparticles as well as bimetallic Au–Pd nanoparticles. These nanoparticles have been characterized with scanning electron microscope, energy dispersive X-ray spectroscopy, X-ray diffraction spectroscopy, and electrochemical techniques. They are further utilized as the catalysts for electrochemical oxidation of hydrazine. The oxidation peak potential is -0.35 and 0.53 V (vs. SCE) when monometallic Pd and Au nanoparticle are used as the catalysts. When bimetallic nanoparticles are applied as the catalyst, their composition affects the peak potential and peak current for the oxidation of hydrazine. Higher oxidation current is achieved when bimetallic Au–Pd nanoparticles with an atomic ratio of 3:1 are deposited on graphene nanoplatelets. Metal nanoparticle-loaded graphene nanoplatelets are thus novel platforms for electrocatalytic, electroanalytical, environmental, and related applications. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Graphene nanoplatelets (GNPs) are the stack of graphene sheets with an overall thickness of about 5 to 25 nm. They have “platelet” mor- phology with a diameter ranging from 0.5 to 25 μm, resulting in high aspect ratios up to the thousands. Their thermal and mechanical prop- erties are similar to carbon nanotubes (CNTs) but their aspect ratios are higher than CNTs. GNPs have been thus widely applied as the elec- trode materials in many fields [1–6], e.g. for sensing applications, for loading catalysts, and for constructing batteries and supercapacitors. We are interested here in applying GNPs as the support (electrode material) for electrochemical oxidation of hydrazine. Hydrazine is a powerful reduction agent and has been used for various applications [6–18]. Since 1960s electrochemical oxidation and detection of hydra- zine has been extensively investigated on various metal electrodes (e.g. platinum, palladium, nickel, cobalt, gold, and silver) [7–12]. On these electrodes reduced overpotentials for the oxidation of hydrazine have been observed. Other solid electrodes, mainly carbon based elec- trodes (e.g. glassy carbon electrode, carbon paste electrode, CNTs, and boron-doped diamond) [13–18] have been utilized. For the oxidation of hydrazine on these electrodes, high overpotentials and small oxida- tion currents have been reported, indicating limited activity towards electrochemical oxidation of hydrazine. To reduce overpotentials and enhance oxidation currents for the oxidation of hydrazine, chemical modification of electrodes (e.g. with transition metal complexes, hydro- quinone derivatives, or metal nanoparticles) [19–23] has been applied. Due to synergetic effect of bimetallic catalysts, bimetallic nanoparticle- modified electrodes have been proved to be one of the most efficient electrode systems. Among many bimetallic nanoparticles, Au and Pd nanoparticles have been approved to be efficient as the catalysts for phosphoric acid fuel cell, CO/H 2 oxidation, oxidation of alcohols, and production of vinyl acetate monomers [6,24–27]. These bimetallic nanoparticle-modified electrodes show more advantages than mono- metallic components [28–30], such as higher catalytic performance, bet- ter sensitivity, and longer stability of electrode systems. However, the application of GNPs as the support to deposit monometallic (e.g. Au and Pd) nanoparticles and bimetallic Au–Pd nanoparticles has not been reported up to now. The application of bimetallic Au–Pd nanoparticles as the catalysts for the oxidation of hydrazine is still missing in literature. Herein we report electrodeposition of monometallic Au and Pd nanoparticles as well as bimetallic Au–Pd nanoparticles on GNPs. The deposition was conducted at a constant potential in a solution of HAuCl 4, H 2 PdCl 4 , or a mixture of HAuCl 4 and H 2 PdCl 4 . In order to vary the composition of bimetallic nanoparticles, the molar concentration ratio (atomic ratio) of HAuCl 4 and H 2 PdCl 4 has been changed from 1:3, 1:1 to 3:1 as some test examples. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectrometry (EDX) has been ap- plied to characterize surface morphologies and to semi-quantitatively determine the compositions of these nanoparticles; X-ray diffraction (XRD) has been used to analyze crystalline structures of these mono- metallic and bimetallic nanoparticles; electrochemical impedance spec- troscopy (EIS) has been utilized to investigate interface properties of these nanoparticle-coated electrodes. For the first time, electrochemical Electrochemistry Communications 29 (2013) 29–32 ⁎ Corresponding author. Tel.: +86 2787194511. ⁎⁎ Corresponding author. Tel.: +49 7615159647. E-mail addresses: qijinwan@mail.wit.edu.cn (Q. Wan), nianjun.yang@iaf.fraunhofer.de (N. Yang). 1388-2481/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.elecom.2013.01.007 Contents lists available at SciVerse ScienceDirect Electrochemistry Communications journal homepage: www.elsevier.com/locate/elecom