Synthesis And Characterization Of Bscf-Mwcnt Modified Electrode As A Potential Oxygen Reduction Cathode In Fuel Cell
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Date
2014-07
Authors
Yusoff, Farhanini
Journal Title
Journal ISSN
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Publisher
Universiti Sains Malaysia
Abstract
A new Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) based composites electrodes for electroreduction of oxygen was developed. The synthesis of pure BSCF using citrate-EDTA complexing method was carried out at pH 5, 7 and 9. It was found that the pH value was crucial for the chelation process as well as for the purity of the phase obtained. Different weight loading of BSCF pH 9 was deposited on a glassy carbon electrode (GCE) and characterized electrochemically. Cyclic voltammograms (CV) showed that the amount of BSCF deposited influenced the electron transfer, mass transport and capacitance behavior. Electrochemical impedance spectroscopy (EIS) indicated that the electrode process was favorable. In this study, the BSCF was modified using multi-walled carbon nanotubes (MWCNT) with the purpose of enhancing the electrode performance. The BSCF-MWCNT composites electrodes was prepared and fabricated using various techniques viz. composites paste electrodes, chemical deposition techniques and in-situ mechanical mixing with modified GCE. The physical and electrochemical properties of the composites electrodes were investigated.
BSCF-MWCNT paste electrode was prepared by direct mixing of BSCF: MWCNT at 90:10, 80:20 and 70:30 (% w/W). The x-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis confirmed the incorporation and the uniform dispersal of MWCNT within BSCF, respectively. The N2 sorption isotherm study showed that the surface area of the composite paste electrode of 58.8 m2 g-1 was obtained and with improvements by four fold from the pure BSCF electrode (14.4 m2 g-1). The EIS and CV demonstrated that the higher ratio MWCNT in the composites was critical in improving the electronic conductivity and kinetics. The modified electrodes were also prepared by deposition of BSCF, MWCNT and BSCF-MWCNT on the surface of GCE. The surface morphology studies showed a uniform distribution of both BSCF and MWCNT on GCE and the MWCNT was homogeneously dispersed on the surface of BSCF for BSCF-MWCNT/GCE. The electrochemical performance of the electrode was enhanced with the addition of MWCNT into the composite and the value of apparent standard rate constant, (kapp) has increased from 3.13 × 10-7 cm s-1 to 2.74 × 10-4 cm s-1 for BCSF/GCE and BSCF-MWCNT/GCE electrode. The BSCF-MWCNT modified GCE was also prepared in-situ by mechanical mixing. The effect of MWCNT loading on the characteristics and performances of the electrode was realised by varying the amount of MWCNT (5, 10, and 20, % w/W). The electron transfer rate constant, (ks) for the modified electrode is directly proportional to the loading amount of MWCNT and vary from 4.25 to 4.88 s-1. The reduction behaviours of BSCF based composites electrodes in 0.1 M KOH were compared by CV and hydrodynamic voltammetry. It was suggested that reduction mechanism of the electrode followed four-electron processes. The high electrocatalytic properties of the modified electrodes in the reaction suggested that it was useful as a material for oxygen reduction in a fuel cell.
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Keywords
Bscf-Mwcnt Modified Electrode , Cyclic Voltammograms (CV) , Electrochemical Impedance Spectroscopy (EIS)