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Volume 104, Issue 5 May 2009 www.sensorsportal.com ISSN 1726-5479

Editor-in-Chief: professor Sergey Y. Yurish, phone: +34 696067716, fax: +34 93 4011989, e-mail: [email protected]

Editors for Western Europe Meijer, Gerard C.M., Delft University of Technology, The Netherlands Ferrari, Vittorio, Universitá di Brescia, Italy Editor South America Costa-Felix, Rodrigo, Inmetro, Brazil Editor for Eastern Europe Sachenko, Anatoly, Ternopil State Economic University, Ukraine

Editors for North America Datskos, Panos G., Oak Ridge National Laboratory, USA Fabien, J. Josse, Marquette University, USA Katz, Evgeny, Clarkson University, USA

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and Technology, Japan Arcega, Francisco, University of Zaragoza, Spain Arguel, Philippe, CNRS, France Ahn, Jae-Pyoung, Korea Institute of Science and Technology, Korea Arndt, Michael, Robert Bosch GmbH, Germany Ascoli, Giorgio, George Mason University, USA Atalay, Selcuk, Inonu University, Turkey Atghiaee, Ahmad, University of Tehran, Iran Augutis, Vygantas, Kaunas University of Technology, Lithuania Avachit, Patil Lalchand, North Maharashtra University, India Ayesh, Aladdin, De Montfort University, UK Bahreyni, Behraad, University of Manitoba, Canada Baoxian, Ye, Zhengzhou University, China Barford, Lee, Agilent Laboratories, USA Barlingay, Ravindra, RF Arrays Systems, India Basu, Sukumar, Jadavpur University, India Beck, Stephen, University of Sheffield, UK Ben Bouzid, Sihem, Institut National de Recherche Scientifique, Tunisia Benachaiba, Chellali, Universitaire de Bechar, Algeria Binnie, T. David, Napier University, UK Bischoff, Gerlinde, Inst. Analytical Chemistry, Germany Bodas, Dhananjay, IMTEK, Germany Borges Carval, Nuno, Universidade de Aveiro, Portugal Bousbia-Salah, Mounir, University of Annaba, Algeria Bouvet, Marcel, CNRS – UPMC, France Brudzewski, Kazimierz, Warsaw University of Technology, Poland Cai, Chenxin, Nanjing Normal University, China Cai, Qingyun, Hunan University, China Campanella, Luigi, University La Sapienza, Italy Carvalho, Vitor, Minho University, Portugal Cecelja, Franjo, Brunel University, London, UK Cerda Belmonte, Judith, Imperial College London, UK Chakrabarty, Chandan Kumar, Universiti Tenaga Nasional, Malaysia Chakravorty, Dipankar, Association for the Cultivation of Science, India Changhai, Ru, Harbin Engineering University, China Chaudhari, Gajanan, Shri Shivaji Science College, India Chavali, Murthy, VIT University, Tamil Nadu, India Chen, Jiming, Zhejiang University, China Chen, Rongshun, National Tsing Hua University, Taiwan Cheng, Kuo-Sheng, National Cheng Kung University, Taiwan Chiang, Jeffrey (Cheng-Ta), Industrial Technol. Research Institute, Taiwan Chiriac, Horia, National Institute of Research and Development, Romania Chowdhuri, Arijit, University of Delhi, India Chung, Wen-Yaw, Chung Yuan Christian University, Taiwan Corres, Jesus, Universidad Publica de Navarra, Spain Cortes, Camilo A., Universidad Nacional de Colombia, Colombia Courtois, Christian, Universite de Valenciennes, France Cusano, Andrea, University of Sannio, Italy D'Amico, Arnaldo, Università di Tor Vergata, Italy De Stefano, Luca, Institute for Microelectronics and Microsystem, Italy Deshmukh, Kiran, Shri Shivaji Mahavidyalaya, Barshi, India Dickert, Franz L., Vienna University, Austria Dieguez, Angel, University of Barcelona, Spain Dimitropoulos, Panos, University of Thessaly, Greece Ding, Jianning, Jiangsu Polytechnic University, China Djordjevich, Alexandar, City University of Hong Kong, Hong Kong

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Microsystems, Italy Francis, Laurent, University Catholique de Louvain, Belgium Fu, Weiling, South-Western Hospital, Chongqing, China Gaura, Elena, Coventry University, UK Geng, Yanfeng, China University of Petroleum, China Gole, James, Georgia Institute of Technology, USA Gong, Hao, National University of Singapore, Singapore Gonzalez de la Rosa, Juan Jose, University of Cadiz, Spain Granel, Annette, Goteborg University, Sweden Graff, Mason, The University of Texas at Arlington, USA Guan, Shan, Eastman Kodak, USA Guillet, Bruno, University of Caen, France Guo, Zhen, New Jersey Institute of Technology, USA Gupta, Narendra Kumar, Napier University, UK Hadjiloucas, Sillas, The University of Reading, UK Hashsham, Syed, Michigan State University, USA Hasni, Abdelhafid, Bechar University, Algeria Hernandez, Alvaro, University of Alcala, Spain Hernandez, Wilmar, Universidad Politecnica de Madrid, Spain Homentcovschi, Dorel, SUNY Binghamton, USA Horstman, Tom, U.S. Automation Group, LLC, USA Hsiai, Tzung (John), University of Southern California, USA Huang, Jeng-Sheng, Chung Yuan Christian University, Taiwan Huang, Star, National Tsing Hua University, Taiwan Huang, Wei, PSG Design Center, USA Hui, David, University of New Orleans, USA Jaffrezic-Renault, Nicole, Ecole Centrale de Lyon, France Jaime Calvo-Galleg, Jaime, Universidad de Salamanca, Spain James, Daniel, Griffith University, Australia Janting, Jakob, DELTA Danish Electronics, Denmark Jiang, Liudi, University of Southampton, UK Jiang, Wei, University of Virginia, USA Jiao, Zheng, Shanghai University, China John, Joachim, IMEC, Belgium Kalach, Andrew, Voronezh Institute of Ministry of Interior, Russia Kang, Moonho, Sunmoon University, Korea South Kaniusas, Eugenijus, Vienna University of Technology, Austria Katake, Anup, Texas A&M University, USA Kausel, Wilfried, University of Music, Vienna, Austria Kavasoglu, Nese, Mugla University, Turkey Ke, Cathy, Tyndall National Institute, Ireland Khan, Asif, Aligarh Muslim University, Aligarh, India Kim, Min Young, Kyungpook National University, Korea South Ko, Sang Choon, Electronics and Telecommunications Research Institute,

Kockar, Hakan, Balikesir University, Turkey Kotulska, Malgorzata, Wroclaw University of Technology, Poland Kratz, Henrik, Uppsala University, Sweden Kumar, Arun, University of South Florida, USA Kumar, Subodh, National Physical Laboratory, India Kung, Chih-Hsien, Chang-Jung Christian University, Taiwan Lacnjevac, Caslav, University of Belgrade, Serbia Lay-Ekuakille, Aime, University of Lecce, Italy Lee, Jang Myung, Pusan National University, Korea South Lee, Jun Su, Amkor Technology, Inc. South Korea Lei, Hua, National Starch and Chemical Company, USA Li, Genxi, Nanjing University, China Li, Hui, Shanghai Jiaotong University, China Li, Xian-Fang, Central South University, China Liang, Yuanchang, University of Washington, USA Liawruangrath, Saisunee, Chiang Mai University, Thailand Liew, Kim Meow, City University of Hong Kong, Hong Kong Lin, Hermann, National Kaohsiung University, Taiwan Lin, Paul, Cleveland State University, USA Linderholm, Pontus, EPFL - Microsystems Laboratory, Switzerland Liu, Aihua, University of Oklahoma, USA Liu Changgeng, Louisiana State University, USA Liu, Cheng-Hsien, National Tsing Hua University, Taiwan Liu, Songqin, Southeast University, China Lodeiro, Carlos, Universidade NOVA de Lisboa, Portugal Lorenzo, Maria Encarnacio, Universidad Autonoma de Madrid, Spain Lukaszewicz, Jerzy Pawel, Nicholas Copernicus University, Poland Ma, Zhanfang, Northeast Normal University, China Majstorovic, Vidosav, University of Belgrade, Serbia Marquez, Alfredo, Centro de Investigacion en Materiales Avanzados, Mexico Matay, Ladislav, Slovak Academy of Sciences, Slovakia Mathur, Prafull, National Physical Laboratory, India Maurya, D.K., Institute of Materials Research and Engineering, Singapore Mekid, Samir, University of Manchester, UK Melnyk, Ivan, Photon Control Inc., Canada Mendes, Paulo, University of Minho, Portugal Mennell, Julie, Northumbria University, UK Mi, Bin, Boston Scientific Corporation, USA Minas, Graca, University of Minho, Portugal Moghavvemi, Mahmoud, University of Malaya, Malaysia Mohammadi, Mohammad-Reza, University of Cambridge, UK Molina Flores, Esteban, Benemérita Universidad Autónoma de Puebla,

Mexico Moradi, Majid, University of Kerman, Iran Morello, Rosario, University "Mediterranea" of Reggio Calabria, Italy Mounir, Ben Ali, University of Sousse, Tunisia Mulla, Imtiaz Sirajuddin, National Chemical Laboratory, Pune, India Neelamegam, Periasamy, Sastra Deemed University, India Neshkova, Milka, Bulgarian Academy of Sciences, Bulgaria Oberhammer, Joachim, Royal Institute of Technology, Sweden Ould Lahoucine, Cherif, University of Guelma, Algeria Pamidighanta, Sayanu, Bharat Electronics Limited (BEL), India Pan, Jisheng, Institute of Materials Research & Engineering, Singapore Park, Joon-Shik, Korea Electronics Technology Institute, Korea South Penza, Michele, ENEA C.R., Italy Pereira, Jose Miguel, Instituto Politecnico de Setebal, Portugal Petsev, Dimiter, University of New Mexico, USA Pogacnik, Lea, University of Ljubljana, Slovenia Post, Michael, National Research Council, Canada Prance, Robert, University of Sussex, UK Prasad, Ambika, Gulbarga University, India Prateepasen, Asa, Kingmoungut's University of Technology, Thailand Pullini, Daniele, Centro Ricerche FIAT, Italy Pumera, Martin, National Institute for Materials Science, Japan Radhakrishnan, S. National Chemical Laboratory, Pune, India Rajanna, K., Indian Institute of Science, India Ramadan, Qasem, Institute of Microelectronics, Singapore Rao, Basuthkar, Tata Inst. of Fundamental Research, India Raoof, Kosai, Joseph Fourier University of Grenoble, France Reig, Candid, University of Valencia, Spain Restivo, Maria Teresa, University of Porto, Portugal Robert, Michel, University Henri Poincare, France Rezazadeh, Ghader, Urmia University, Iran Royo, Santiago, Universitat Politecnica de Catalunya, Spain Rodriguez, Angel, Universidad Politecnica de Cataluna, Spain Rothberg, Steve, Loughborough University, UK Sadana, Ajit, University of Mississippi, USA Sadeghian Marnani, Hamed, TU Delft, The Netherlands Sandacci, Serghei, Sensor Technology Ltd., UK Sapozhnikova, Ksenia, D.I.Mendeleyev Institute for Metrology, Russia Saxena, Vibha, Bhbha Atomic Research Centre, Mumbai, India

Korea South Schneider, John K., Ultra-Scan Corporation, USA Seif, Selemani, Alabama A & M University, USA Seifter, Achim, Los Alamos National Laboratory, USA Sengupta, Deepak, Advance Bio-Photonics, India Shankar, B. Baliga, General Monitors Transnational, USA Shearwood, Christopher, Nanyang Technological University, Singapore Shin, Kyuho, Samsung Advanced Institute of Technology, Korea Shmaliy, Yuriy, Kharkiv National University of Radio Electronics,

Ukraine Silva Girao, Pedro, Technical University of Lisbon, Portugal Singh, V. R., National Physical Laboratory, India Slomovitz, Daniel, UTE, Uruguay Smith, Martin, Open University, UK Soleymanpour, Ahmad, Damghan Basic Science University, Iran Somani, Prakash R., Centre for Materials for Electronics Technol., India Srinivas, Talabattula, Indian Institute of Science, Bangalore, India Srivastava, Arvind K., Northwestern University, USA Stefan-van Staden, Raluca-Ioana, University of Pretoria, South Africa Sumriddetchka, Sarun, National Electronics and Computer Technology

Center, Thailand Sun, Chengliang, Polytechnic University, Hong-Kong Sun, Dongming, Jilin University, China Sun, Junhua, Beijing University of Aeronautics and Astronautics, China Sun, Zhiqiang, Central South University, China Suri, C. Raman, Institute of Microbial Technology, India Sysoev, Victor, Saratov State Technical University, Russia Szewczyk, Roman, Industrial Research Institute for Automation and

Measurement, Poland Tan, Ooi Kiang, Nanyang Technological University, Singapore, Tang, Dianping, Southwest University, China Tang, Jaw-Luen, National Chung Cheng University, Taiwan Teker, Kasif, Frostburg State University, USA Thumbavanam Pad, Kartik, Carnegie Mellon University, USA Tian, Gui Yun, University of Newcastle, UK Tsiantos, Vassilios, Technological Educational Institute of Kaval, Greece Tsigara, Anna, National Hellenic Research Foundation, Greece Twomey, Karen, University College Cork, Ireland Valente, Antonio, University, Vila Real, - U.T.A.D., Portugal Vaseashta, Ashok, Marshall University, USA Vazquez, Carmen, Carlos III University in Madrid, Spain Vieira, Manuela, Instituto Superior de Engenharia de Lisboa, Portugal Vigna, Benedetto, STMicroelectronics, Italy Vrba, Radimir, Brno University of Technology, Czech Republic Wandelt, Barbara, Technical University of Lodz, Poland Wang, Jiangping, Xi'an Shiyou University, China Wang, Kedong, Beihang University, China Wang, Liang, Advanced Micro Devices, USA Wang, Mi, University of Leeds, UK Wang, Shinn-Fwu, Ching Yun University, Taiwan Wang, Wei-Chih, University of Washington, USA Wang, Wensheng, University of Pennsylvania, USA Watson, Steven, Center for NanoSpace Technologies Inc., USA Weiping, Yan, Dalian University of Technology, China Wells, Stephen, Southern Company Services, USA Wolkenberg, Andrzej, Institute of Electron Technology, Poland Woods, R. Clive, Louisiana State University, USA Wu, DerHo, National Pingtung University of Science and Technology,

Taiwan Wu, Zhaoyang, Hunan University, China Xiu Tao, Ge, Chuzhou University, China Xu, Lisheng, The Chinese University of Hong Kong, Hong Kong Xu, Tao, University of California, Irvine, USA Yang, Dongfang, National Research Council, Canada Yang, Wuqiang, The University of Manchester, UK Yaping Dan, Harvard University, USA Ymeti, Aurel, University of Twente, Netherland Yong Zhao, Northeastern University, China Yu, Haihu, Wuhan University of Technology, China Yuan, Yong, Massey University, New Zealand Yufera Garcia, Alberto, Seville University, Spain Zagnoni, Michele, University of Southampton, UK Zamani, Cyrus, Universitat de Barcelona, Spain Zeni, Luigi, Second University of Naples, Italy Zhang, Minglong, Shanghai University, China Zhang, Qintao, University of California at Berkeley, USA Zhang, Weiping, Shanghai Jiao Tong University, China Zhang, Wenming, Shanghai Jiao Tong University, China Zhong, Haoxiang, Henan Normal University, China Zhu, Qing, Fujifilm Dimatix, Inc., USA Zorzano, Luis, Universidad de La Rioja, Spain Zourob, Mohammed, University of Cambridge, UK

Sensors & Transducers Journal (ISSN 1726-5479) is a peer review international journal published monthly online by International Frequency Sensor Association (IFSA). Available in electronic and on CD. Copyright © 2009 by International Frequency Sensor Association. All rights reserved.

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Volume 104 Issue 5 May 2009

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Research Articles

Biosensors Development Based on Potential Target of Conducting Polymers Ravindra P. Singh and Jeong-Woo Choi............................................................................................ 1 Designing Binocular Stereo Omni-Directional Vision Sensors Yi-ping Tang, Chen-jun Pang, Yi-hua Zhu ......................................................................................... 19 A Stainless Steel Electrode Phantom to Study the Forward Problem of Electrical Impedance Tomography (EIT) Tushar Kanti Bera and J. Nagaraju..................................................................................................... 33 Single-mode D-type Optical Fiber Sensor in Spectra Method at a Specific Incident Angle of 89° Ming-Hung Chiu, Po-Chin Chiu, Yi-Hsien Liu, Wei-Ding Zheng ........................................................ 41 Effect of Low Frequency Pulsed DC on Human Skin in Vivo: Resistance Studies in Reverse Iontophoresis Pavan Kumar Kathuroju and Nagaraju Jampana............................................................................... 47 Low Frequency Noises of Hydrogen Sensors Zara Mkhitaryan, Ferdinand Gasparyan, Armine Surmalyan............................................................. 58 Fe2O3 - ZnO Based Gas Sensors L. A. Patil ............................................................................................................................................ 68 Effect of Yttria on Gas Sensitivity of Tungsten Trioxide M. H. Shahrokh Abadi, M. N. Hamidon, Rahman Wagiran, Abdul Halim Shaari, Norhisam Misron, Norhafizah Abdullah. .......................................................................................................................... 76 Liquefied Petroleum Gas (LPG) Sensing Properties of Nanosized Sprayed CdIn2O4 Thin Films R. J. Deokate, R. R. Salunkhe, K. Y. Rajpure.................................................................................... 87 Optimization of a Novel Humidity Sensing Mechanism Strip Length Souhil Kouda, Zohir Dibi, Abdelghani Dendouga, Samir Barra.......................................................... 96 Humidity Sensing Studies of WO3-ZnO Nanocomposite N. K. Pandey, Anupam Tripathi, Karunesh Tiwari.............................................................................. 109 Electrochemical Reduction of Potassium Ferricyanide Mediated by Magnesium Diboride Modified Carbon Electrode WeeTee Tan, Farhan Yusri and Zulkarnain Zainal ............................................................................ 119 Authors are encouraged to submit article in MS Word (doc) and Acrobat (pdf) formats by e-mail: [email protected] Please visit journal’s webpage with preparation instructions: http://www.sensorsportal.com/HTML/DIGEST/Submition.htm

International Frequency Sensor Association (IFSA).

Sensors & Transducers Journal, Vol. 104, Issue 5, May 2009, pp. 119-127

119

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Electrochemical Reduction of Potassium Ferricyanide Mediated by Magnesium Diboride Modified Carbon Electrode

*WeeTee TAN, FARHAN Yusri and ZULKARNAIN Zainal Department of Chemistry, Faculty of Science, Universiti Putra Malaysia,

43400 UPM, Serdang, Selangor D.E., Malaysia E-mail: [email protected]

Received: 10 February 2009 /Accepted: 19 May 2009 /Published: 25 May 2009 Abstract: Use of a glassy carbon (GC) modified by adhered microparticles of MgB2 mediates the reduction process of Fe(III)(CN)6

3- during cyclic voltammetry. Peak potential was observed to shift slightly to less negative value by about 50 mV and current is significantly enhanced by about two folds. The sensitivity under conditions of cyclic voltammetry is significantly dependent on pH, electrolyte and scan rate. The result of scanning electron micrograph of MgB2 obtained before and after electrolysis show the size increased slightly to the size ranging from 2 - 5.5 µm attributing to the hydration effect and/or incorporation of some ionic species into the crystal lattices of MgB2. Interestingly, redox reaction of Fe(III) solution using modified GC electrode remain constant even after 15 cycling. It is therefore evident that the MgB2 modified GC electrode posseses some degree of stability. Potential use of MgB2 as a useful electrode material is therefore clearly evident. Copyright © 2009 IFSA. Keywords: Solid state voltametry of microparticles, MgB2 modified GC electrode, Fe(III)/(II) redox couple, Electrocatalysis 1. Introduction Magnesium diboride (MgB2) is an odourless and brittle compound, exists in the form of powder, crystals and ceramics where the colour varies from one form to the other; black in powder, yellow in crystals and pink in ceramics. It has simple crystal structure with Mg layer alternating with honeycomb B layer [1]. It is also a simple binary compound which contains only 3 atoms per hexagonal cell. In year 2001, Jun Akamitsu et al. discovered that Tc for MgB2 is 39 k. The Tc is double from previous


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record of intermetallic Tc [1]. The isotopes studies in previous report showed that Tc was shifted by 1 K if MgB2 with B10 isotope was used instead of MgB2 with B11 isotope [2,3] while there was no effect when change from isotope Mg 24 to isotope Mg 25 [3]. There is a growing consensus that the electro-phonon interaction is responsible for the superconductivity [4]. It was not discovered 40 years ago due to difficulty in preparation [1]. However, recently method of growing MgB2 such as single crystal [5], powder [6], and wires [7] have been developed. In application it can be used as a magnet due to light weight for magnetic-resonans-imaging application [1]. The study of electrochemistry for MgB2 is still rather lacking. Electrochemical characterization and mediation studies using MgB2 modified solid electrode has not been reported. In this work, an attempt is made to report the work done using MgB2 as sensing electrode materials which is mechanically attached to the surface of glassy carbon (GC) working electrode via solid phase voltammetry of microparticles (SPVM). 2. Experimental 2.1. Instrument and Electro Analytical Analysis Methods Electrochemical workstations of Bioanalytical System Inc. USA: Model BAS 50W with potentiostat driven by electroanalytical measuring software were connected to PC computer to perform cyclic voltammetry (CV), chronoamperometry (CC), and chronoamperometry (CA). An Ag/AgCl (3M NaCl) and platinum wire were used as a reference and counter electrodes respectively. The working electrode used in this study was 3 mm diameter glassy carbon (GC). Unless otherwise stated, the voltammetric experiments were carried out at 25 ± 2oC using 1.0M KCl as supporting electrolyte. Solution was degassed with nitrogen for ten minutes prior to recording the voltammogram. 2.2. Reagents All reagents were analytical reagent or electrochemical grade purity. All solutions were prepared using distilled water. Unless otherwise specified, the supporting electrolyte was 1.0 M KCl in aqueous media at room temperature. 2.3. Procedures The solid compound magnesium diboride (MgB2) was transferred to the surface of the glassy carbon (GC) electrode as followed: Sample amount of 1-3 mg of MgB2 were placed on a coarse grade filter paper. Glassy carbon was pressed onto the substance and rubbed over the material, causing some compound to adhere to the electrode surface. For electrochemical measurements, the electrode was transferred into the solution. The clean glassy carbon surface could be renewed after the measurement by polishing with 0.5 µm alumina slurry, followed by ultrasonic cleaning for about 2-3 minutes, rinsing with distilled water. 3. Result and Discussion 3.1. Characterization of Magnesium Diboride Using Different Solid State Electrodes Fig. 1 shows the cyclic voltammograms of using the bare GC working electrode and MgB2 modified GC electrode in 0.1 M KCl supporting electrolytes. The working potential window (where electroactivity due to electrode materials and electrolyte is negligible) was found to be in the range of -1.0 to at least 1.0 V and 0.0 V to -1.30 V for bare GC electrode and MgB2 modified GC electrode


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during the initial potential cycle. A considerable extension of the working window at the cathodic region is observed when MgB2 modified GC is used. Although the working window at anodic region is deteriorating due to the “electrocatalysed” oxidation of the aqueous electrolyte or the reactivity of MgB2 microparticles giving rise to a limiting current appearing at about 0.2 V. This limiting current, however diminishes in subsequent cycle (2nd cycle) allowing potential working window to be widened at the anodic region to near 0.8 V. It shows that MgB2 modified GC electrode is useful for redox reaction studies appearing at a more negative potential of up to at least -1.3 volt and is only useful at anodic region if 2nd cycle is used.

Fig. 1. Cyclic voltammogram (Background) obtained for the bare GC working electrode (a) and magnesium diboride modified GC electrode (b) in 0.1M potassium chloride.

Fig. 2 shows the CV of 0.1 M KCl taken at varying working electrodes modified with magnesium diboride in 0.1M KCl. The MgB2 modified solid electrodes exhibit potential working range of -1.3 to 0.6 V, -0.8 to 0.6 V and -0.4 to 0.6 V for GC, Pt and Au electrodes respectively. Hence in terms of the degree of accessibility of potential working window for various solid electrodes, GC > Pt > Au. It is interesting to note that both GC and Au modified electrodes have quite a similar background / capacitance current despite the fact that GC electrode (3 mm diameter) used has a larger surface area than that of Au (1 mm diameter).

Fig. 2. Cyclic voltammetry obtained for the (a) GC (b) pt (c) gold electrode modified with magnesium diboride in 0.1M potassium chloride, scan rate 100 mV/s.


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3.2. Electrochemical Characterization in Electrolyte of Varying pH For these studies, the pH of 0.1M KCl solution was varied by addition of either dil. HNO3 or KOH solution. The cyclic voltammograms obtained (Fig. 3) in 0.1M KCL at neutral (pH7) and basic (pH12) solution were found to be similar with working potential region detected between -1.3 V and 0.6 V while in a more basic solution of greater than pH 12, the working potential range is widened to a more positive potential by 200 mV (ie to - 0.8 V. However, in acidic solution (pH4), the working range was shortened to between -0.8 V and 0.4 V due to the reduction of hydrogen gas in acidic solution and oxidation of the aq. electrolyte. There is a small peak appearing at near 0 V probably due to the oxidation of oxygen trapped inside the magnesium diboride. As MgB2 modified solid electrode based on glassy carbon, GC possesses characteristics of a more superior working electrode, it is therefore used in subsequent studies.

Fig. 3. Cyclic voltammetry obtained for the GC electrode modified with magnesium diboride in 0.1 M potassium chloride at (a) pH7 (b) pH4 (c) pH10, scan rate 100 mV/s.

3.3. Effect of Magnesium Diboride Modified GC Electrode on the Redox Reaction

of Potassium Ferricyanide During CV Potassium Ferricyanide is commonly used as a reference standard for the purpose of calibrating a voltammetric system in aqueous solutions. During the calibration process of an electroanalytical workstation (BAS Model 50W) using GC and MgB2 modied GC electrode. Oxidative current of Fe3+/Fe2+ redox couple appears to be significantly enhanced (Fig. 4).

Fig. 4. Cyclic voltammetry of 1mM potassium ferricyanide in 0.1M potassium chloride, at scan rate 100 mV/s for the GC unmodified working electrode and GC electrode modified with magnesium diboride.


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It was also observed that the redox potential with Ea = 227 mV and Ec= 320 mV with peak separation of 93 mV (for n=1) in 0.1M KCl electrolyte indicating the reversible reaction of the Fe(III)/Fe(II) couples in KCl solution and agree well with the accepted values. In subsequent studies, various chemical and physical effects were assessed in order to determine the optimum conditions under which maximum current response at the MgB2 modified GC electrode can be obtained. 3.4. Effect of Varying Supporting Electrolyte The different type of supporting electrolyte exerts slight influence on the reduction peak potential of Fe3+ as expected esp. in noncomplexing solutions (Table 1). In general, redox peaks of Fe3+ appearing at have a similar pattern of peak formation in varying supporting electrolyte. However, redox current esp. the oxidation peak of Fe3+/Fe2+ couple show that the greatest enhancement effect is obtained when potassium chloride is used as electrolyte. In general, degree of current enhancement in varying electrolyte varies in the following order:

KCl > KH2PO4 > KNO3 > KClO4 > K2 SO4 (Table 1).

Table 1. Cyclic voltammetry of 1mM potassium ferricyanide in different electrolyte, at scan rate 100 mV/s for the GC unmodified working electrode and GC electrode modified with magnesium diboride.

Reduction

Current/µA Solution Without MgB2

With MgB2

Enhancement

0.1M Potassium oxalate 15.34 16.10 1.05 0.1M Potassium dihidrogen orthophosphate 12.55 15.98 1.27

0.1M Potassium nitrate 15.14 16.19 1.07 0.1M Potassium chloride 12.49 23.60 1.89

3.5. Effect of Varying pH The solution was varied from 2.0 to 12.0 in order to determine its effect on the catalytic reduction of potassium ferrricyanide at the magnesium diboride modified electrode. Table 1 and Fig. 5 show that the highest current was observed under a neutral condition. A much higher current is generally observed in acidic media as compared with those in a more basic solution. It is as expected as Fe(III) hydrolysis sets in under strongly alkaline conditions. The hydrolysed Fe(III) product is usually electroinactive. 3.6. Effect of Potential Cycling The potential cycling of the reduction of Fe(III) solution, 1.0 mM K3Fe(CN)6 was carried out at the electrode surface of a glassy carbon electrode (3 mm diameter) modified with MgB2 microparticles during cyclic voltammetry. Continuous potential cycling did not seem to affect the redox current of potassium ferrricyanide at magnesium diboride modified GC electrode since the faradaic activity appears reproducible even after 15 cycles reflecting the stability of the MgB2 coat/film at the surface of GC electrode (see also SEM results given below).


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Graph Current vs pH

010203040

50607080

0 5 10 15pH

Curren

t/µA

Fig. 5. Cyclic voltammetry of 1mM potassium ferricyanide diboride in different pH, at scan rate 100 mV/s for the GC modified electrode with magnesium diboride.

3.7. Effect of Varying Fe(III) Concentration Linear current dependent on K3Fe(CN)6 concentration was observed up to 10 mM described by the equation of y=40.02x+12.90 with R2=0.9854. The slope of 40.0 mALmol-1 K3Fe(CN)6 showed high sensitivity response is readily obtained using MgB2 modified GC electrode. 3.8. Effect of Varying Scan Rate The effect of varying scan rates on the cyclic voltammograms of 1 mM Ferricyanide using magnesium diboride as working electrode 1.0 M KCl supporting electrolyte was studied over 5 – 1000 mV/s. Oxidation and reduction currents of Fe(III)/Fe(II) couple was observed to increase with scan rate due to heterogeneous kinetics. Based on a plot of log (peak current) versus log (scan rate, v) for reduction current of the first cycle, a straight line was obtained fulfilling the equation y = 0.565 x + 0.249 with R2=0.9886. A slope of 0.57 which is quite comparable with theoretical slope of 0.5 for diffusion controlled process. 3.9. Chronoamperometry In Chronoamperometry (CA) the potential is stepped from an individual value Ei to Et and the accompanying current is recorded as a function of time for an electrode in unstirred solution [14].The current decays as the electrolysis proceeds to deplete the solution near the electrode of electroinactive species. The current response is described by the Cottrell equation: I = nFAC(D/πt)1/2 (1) where I = Current n = Number of electron per molecule F = Faraday constant A = Electrode area D = Diffusion coefficient of electroactive species C = Concentration of electroactive species T = Time


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Fig. 6 shows the monotonous rising and decaying current transient in accordance to the diffusion process based on the diffusion process to a planar electrode.

Fig. 6. Chronoamperograms of 1mM potassium ferricyanide in 0.1M potassium chloride for the GC modified electrode with magnesium diboride.

3.10. Chronocoulometry Chronocoulometry (CC) is the integral analogs of the corresponding chronoamperometry approaches. The integral of the Cottrell equation gives the cumulative charge passed in reducing or oxidizing the diffused component [14]: Q = 2nFAD1/2Co

2π1/2t1/2 (2) where Q = Charge and the other parameters have its usual meanings. The analysis of chronocoulometry (CC) data is based on the Anson equation above (Eq. 2), which defines the charge-time dependence for linear diffusion control. The Anson plot shows linear dependency of Q upon t1/2 (Fig. 7) indicating that the process involved is diffusion controlled. Based on Anson’s plot of the above, surface charge can be calculated by taking the difference between two intercepts of forward and reverse steps at t=0. It was found that the MgB2/GC has a total charge transferred of 3.13 µC when 1mM potassium ferricyanide was reduced.

Fig. 7. Chronocoulograms of 1mM potassium ferricyanide in 0.1M potassium chloride for the GC modified electrode with magnesium diboride.


126

3.11. Scanning Electron Microscopy As is shown in Fig. 8, prior to the application of a reducing potential, magnesium diboride had a size range of the order of 0.5 to 1.3 µm. After controlled-potential electrolysis was carried out in the presence of K3Fe(CN)6, the size increased slightly to the size ranging from 2 - 5.5 µm attributing to the hydration effect and/or incorporation of some ionic species into the crystal lattices of MgB2.

(a)

(b)

Fig. 8. Scanning electron micrographs of magnesium diboride microparticles mechanically attached to a basal plane pyrolitic graphite electrode (a) before and (b) after electroanalysis.

4. Conclusion Among the various solid electrodes used, GC electrode by far a better choice of solid state electrode to be modified with MgB2 micropartic; les as it has an extended negative potential working region under weakly acidic to strongly alkaline region. Although the oxidative region is limited, the use of potential cycling helps to widen the oxidative working potential range significantly. Use of a glassy carbon (GC) modified by adhered microparticles of MgB2 mediates the reduction process of Fe(III)(CN)6

3- during cyclic voltammetry. Peak potential shifts slightly to less negative value by about 50 mV and current is significantly enhanced by about two folds. The sensitivity under conditions of cyclic voltammetry is significantly dependent on pH, electrolyte and scan rate. The stability of MgB2 film coated at the GC electrode surface is also evident from SEM and potential cycling experiments. Potential use of MgB2 as a useful electrode material is therefore clearly evident. Acknowledgement The authors wish to thank Ministry of Science, Technology and Innovation, Malaysia (MOSTI) for a research grant and Universiti Putra Malaysia for the use of research facilities, One of us (F.Y.) expresses appreciation of obtaining a research assistantship via the MOSTI’s grant. References [1]. Paul C. Canfield and George W. Crabtree, Magnesium Diboride: Better Late than Never, Physics Today,

March 2003, pp. 34-40.


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[2]. S. L. Bud’ko et al, Boron isotope effect in superconducting MgB2, Phys. Rev. Lett., 86, 2001, pp. 1877. [3]. D. G. Hinks et al, The complex nature of superconductivity in MgB2 as revealed by the reduced total

isotope effect, Nature, 411, 2001, p. 457. [4]. I. I. Mazin et al, Electronic structure, electron–phonon coupling, and multiband effects in MgB2, Physica

C, 385, 2003, pp. 49-65. [5]. S. Strässle et al, 11B NMR study of single-crystal MgB2 in the normal conducting phase, Physica C, 466,

2007, pp. 168-173. [6]. R. H. T. Wilke et al, Synthesis of Mg(B1−xCx)2 powders, Physica C, 432, 2005, pp. 193-205. [7]. B. Birajdar et al, Correlation of superconducting properties and microstructure of MgB2 wires and tapes,

Physica C, 460-462, 2007, pp. 1409–1410. [8]. C.-C. Hu and C.-C. Wang, Nanostructures and Capacitive Characteristics of Hydrous Manganese Oxide

Prepared by Electrochemical Deposition, J. Electrochem. Soc., 150, 2003, pp. A1079. [9]. S. Devaraj and N. Munichandraiah, Electrochemical Supercapacitor Studies of Nanostructured α-MnO2

Synthesized by Microemulsion Method and the Effect of Annealing, J. Electrochem. Soc., 154, 2007, pp. A80.

[10]. S. R. Sivakkumar, Jang Myoun Ko, Dong Young Kim, B. C. Kim and G. G. Wallace, Performance evaluation of CNT/polypyrrole/MnO2 composite electrodes for electrochemical capacitors, Electrochimica Acta, 52, 2007, pp. 7377-7385.

[11]. Michael J. Dinsmore and Jeremy S. Lee, Hexachloroiridate(IV) as a redox probe for the electrochemical discrimination of B-DNA and M-DNA monolayers on gold, Journal of Electroanalytical Chemistry, 617, 2008, pp. 71-77.

[12]. Reza Karimi Shervedani, Fatemeh Yaghoobi, Abdolhamid Hatefi-Mehrjardi and Saied Mohsen Siadat-Barzoki, Electrocatalytic activities of gold-5-amino-2-mercaptobenzimidazole-Mn+ self-assembled monolayer complexes (Mn+: Ag+, Cu2+) for hydroquinone oxidation investigated by CV and EIS, Electrochimica Acta, 53, 2008, pp. 4185-4192.

[13]. Maoguo Li, Feng Gao, Ping Yang, Lun Wang and Bin Fang, Conveniently assembling dithiocarbamate and gold nanoparticles onto the gold electrode: A new type of electrochemical sensors for biomolecule detection, Surface Science, 602, 2008, pp. 151-155.

[14]. Instruction manual, CV 50W, version 2. Bioanalytical System, Inc. USA, Feb, 1996.

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