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Title:	Manganese oxide/functionalized carbon nano tube nanocomposite as catalyst for oxygen reduction reaction in microbial cell
Authors:	Liew Kien Ben (P67977)
Supervisor:	Wan Ramli Wan Daud, Prof. Dato' Ir. Dr.
Keywords:	Microbial cell Electrocatalyst Manganese oxide Oxygen reduction Universiti Kebangsaan Malaysia -- Dissertations
Issue Date:	1-May-2016
Description:	Microbial fuel cell (MFC) have been perceived as new-developed technology that able to generate electricity coupled to oxidation of organic contaminants in wastewater by electrochemically active microorganism. However, the high cost and limited availability of conventional Pt as oxygen reduction reaction catalyst have restricted the commercialization of MFC. To resolve this problem, it is necessary to develop an active electrocatalyst in order to improve the power generation of MFC; meanwhile replacing utilization of precious metal. This studies focused on the synthesis, characterization and investigation on the oxygen reduction reaction (ORR) kinetic and mechanism of manganese oxide and functionalized carbon nanotube nanocomposite (MnO2/f-CNT). The activity of MnO2 was compared with other transition metal oxide namely FeO, CuO, CoO and NiO. MnO2 was found to exhibited highest onset potential at 0.0 V in phosphate buffer solution medium. The pristine CNT was acid-treated to functionalize the surface of CNT and manganese oxide was then deposited on the CNT wall. After that, the self-synthesized MnO2/f-CNT and functionalized CNT (f-CNT) was characterized by field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), Raman spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The catalytic activity and ORR kinetic of these catalysts were evaluated by cyclic voltammetry (CV), rotating disk electrode (RDE) and rotating ring disk electrode (RRDE). From the surface analysis, surface defect was found on the surface of f-CNT and it was further proved the increase of ID/IG ratio by Raman spectroscopy. FESEM and TEM analysis also showed that nano-sized manganese oxide crystal was evenly deposited on the outer surface of f-CNT. Result of XRD showed that crystal structure of manganese oxide was ε-MnO2. Kinetic study of MnO2/f-CNT was carried in both neutral and alkaline media (0.1 M KOH). From the K-L plot, ORR electron transferred number in alkaline media (n=3.73) was higher than in neutral media (n=3.07). The electron transferred number obtained from RRDE was almost similar with value of 3.30 in neutral media and 3.64 in alkaline media. Therefore, it was concluded that MnO2/f-CNT catalyzes ORR more effectively in alkaline condition. Using Tafel approach to ORR kinetic, two different Tafel slope were identified. At low current density region, Tafel slope of 108 mV dec-1 and 145 mV dec-1 were attained in neutral media and alkaline media. While at high current density region, the Tafel slopes were shifted to 180 mV dec-1 in neutral media and 172 mV dec-1 in alkaline media. When MnO2/f-CNT was applied as cathode catalyst in MFC, it produced maximum power density of 589 mW m-2 which is comparable with MFC equipped with Pt/C (623 mW m-2). Furthermore, MFC equipped with this catalyst displayed COD removal higher than 85% and coulombic efficiency of 27.6% which is higher than those achieved by Pt/C. The adsorption of atomic and molecular oxygen on MnO2 (110) surface was also studied by using density functional theory (DFT). Atomic oxygen can be adsorbed at most of the possible site due to its more reactive properties. However, for molecular oxygen adsorption, only site 6 was found to be energetically favorable for adsorption. In addition, different adsorption configuration of oxygen molecule can produce different intermediate or end product. Simulation of ORR on MnO2 (110) surface showed that oxygen can be reduced to 4 OH- ions via two and four electrons transfer pathway.,Ph.D.
Pages:	174
Publisher:	UKM, Bangi
Appears in Collections:	Fuel Cell Institute / Institut Sel Fuel

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