Browsing by Author "Admassie, Shimelis (Professor)"

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    Conducting Polymer Based Composites for Electrocatalytic Reduction of Oxygen and Flexible Supercapattery
    (Addis Ababa University, 2020-12-13) Getachew, Teklewold; Admassie, Shimelis (Professor)
    The rapid depletion of fossil fuels and the growing environmental impact of traditional energy resources have created the need to develop more efficient, low cost and environmentally friendly energy conversion and storage devices like solar cells, fuel cells, batteries and supercapacitors. In this PhD work, the application of conducting polymer based composites for electrocatalytic reduction of oxygen in fuel cell and supercapattery have been investigated. To reduce the amount of expensive and scarce platinum metal that is used in the electrocatalytic reduction of oxygen, composites of graphene oxide (GO) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) were investigated as a conductive support for Pt nanoparticles. The surface characteristics of the materials were examined using atomic force microscopy (AFM), X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and energy-dispersive X-ray spectroscopy (EDS). Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) at rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) were used to characterize the electrocatalytic activities of the composite materials. The structural and electrochemical studies reveal that the addition of ethylene glycol (EG) favors the homogeneous distribution of Pt particles with reduced particle size and improves the electrocatalytic properties. A 30% and 16% increase in electrochemically active surface area (ECSA), a 1.2 and 1.1 fold in specific area activity (SA), and a 1.5 and 1.2 fold in mass activity (MA) were observed for 30% and 40% Pt loading, respectively, on PEDOT:PSS. A composite of reduced graphene oxide (rGO) and PEDOT:PSS (EG) was investigated for different (w/w) ratio of PEDOT:PSS and rGO. The 1:2 w/w ratio showed an enhanced catalytic activity with high limiting current, more positive onset potential, higher SA and MA with lower H2O2 yield compared to PEDOT:PSS (EG) and rGO. Furthermore, composites of rGO and conducting Teklewold Getachew Page vii polymers synthesized from 8-amino-2-naphthalene sulfonic acid (8-ANSA), 5-amino-1-naphthalene sulfonic acid (5-ANSA), 2-amino-1-naphthalene sulfonic acid (2-ANSA), and 4-amino-1-naphthalene sulfonic acid (4-ANSA) were prepared for use as metal-free electrocatalyst in oxygen reduction reaction (ORR). The best performing polymer composite was found to be GC/poly(8-ANSA)/rGO, with an enhanced electrocatalytic activity over the rGO and poly(8-ANSA) only films. More than 100 mV positive shift in the onset potential and 1.6 times increase in current density were observed. Density functional theory (DFT) calculations also confirmed the experimentally observed catalytic activities of 2-ANSA, 4-ANSA, 5-ANSA and 8-ANSA. The application of roll-to-roll printed PEDOT:PSS, Lg/PEDOT:PSS, Mo/PEDOT:PSS, and Lg/Mo/PEDOT:PSS on flexible indium tin oxide/polyethylene terephthalate (ITO/PET) were investigated for supercapattery in neutral aqueous and gel electrolyte. The PEDOT:PSS/ITO/PET electrode achieved 2.2 mAh cm-2 (46.5 mAh g-1) in 0.1 M NaCl and 10 mAh cm-2 (216.8 mAh g-1) in 2 mM Pb2+/0.1 M NaCl at a current density of 0.2 mA cm-2 (4.34 A g-1). A device operating at a high voltage of 1.8 V was built using PEDOT:PSS/ITO/PET in aqueous electrolyte. The energy density of the symmetric PEDOT:PSS/ITO/PET device was found to be 6.2 Wh kg-1 in 0.1 M NaCl and improved to 11 Wh kg-1 in 3 mM Pb2+/0.1 M NaCl. The PEDOT:PSS/ITO/PET electrode delivers a specific capacity of 20.88 mAh g-1 (75.2 C g-1) and increased to 90.6 mAh g-1 (326.1 C g-1), to 103.1 mAh g-1 (371 C g-1), and 303.1 mAh g-1 (1091 C g-1) at 1 A g-1 for Mo/PEDOT:PSS/ITO/PET, Lg/PEDOT:PSS/ITO/PET and Mo/Lg/PEDOT:PSS/ITO/PET, respectively in 0.1 M HClO4. Mo/Lg/PEDOT:PSS/ITO/PET electrode exhibits an energy density of 1.9 mWh cm-3 as a sandwich-type symmetric gel-based device at a power density of 22 mW cm-3.