Browsing by Author "Ji, S"

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    Lanthanum modified Fe3N/carbon foam as highly efficient electrode for zinc-air batteries
    (Journal of Alloys and Compounds, 2023) Wang, M; Linkov, V; Ji, S
    Efficient electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are of great importance for large-scale application of rechargeable zinc-air batteries. Iron-nitrogen-carbon materials are known for their excellent ORR catalytic activity, but it is their low OER performance that is responsible for poor charging operation causing slow market adoption of these energy storage devices. Herein, lanthanum (La) is applied to enhance OER electrocatalytic properties of iron-nitrogen-carbon materials used as zinc-air battery electrodes. According to X-ray diffractometry, the presence of La alters the electronic structure of surrounding N and Fe elements, resulting in more negative N and positive Fe ions to appear on the surface and form Fe3N active species. Electrochemical analysis demonstrated enhanced bi-functional electrocatalytic performance of La-modified Fe3N carbon foam (La-Fe0.1:1/NFC) which total overpotential was among the lowest of previously reported metal-nitrogen-carbon materials. La-Fe0.1:1/NFC exhibited high power density and charge-discharge cycling stability in a real zinc-air battery cell.
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    Supercapacitor electrode materials based on nanostructured conducting polymers and metal oxides
    (University of the Western Cape, 2013) Gcilitshana, Oko Unathi; Ji, S
    Supercapacitors are charge-storage devices. Compared to batteries, they have higher power density, more excellent reversibility and longer cycle life. Therefore, supercapacitors have played an increasingly important role in the fields of power source especially in automotive applications, such as electric and hybrid electric vehicles. The higher power density of supercapacitors offers improved vehicle acceleration and the ability to recover more energy from regenerative breaking, since they can be charged and discharged at high current. Generally, the key for supercapacitors to achieve high specific power depends on the inherent properties and the surface areas of their electrode materials. Therefore, current research in the field of supercapacitors has been carried out with increased emphasis on the development of new electrode materials. Optimal novel synthesis of electrode materials for supercapacitor application in hybrid vehicles was accomplished with polypyrrole nanowires, manganese oxide and its carbon composites, ruthenium oxide and its carbon composites being the products. A set of structural and chemical parameters influencing the performance of synthesized electrode materials were identified. Parameters included crystallinity, particle size, particle size distribution, surface area, electrochemical activity. A large range of analytical tools were employed in characterizing the electrode materials of interest. High accuracy and precision in the quantitative and qualitative structural characterization of electrode materials collected by x-ray diffractometry, transmission electron microscopy, scanning electron microscopy and Fourier transform infra-red spectroscopy was demonstrated. N₂-physisorption produced surface area and pore size distribution data of high quality. Cyclic voltammetry, charge and discharge cycling, electron impedance spectroscopy were employed in the electrochemical characterization of the synthesized electrode materials and both qualitative and quantitative information obtained. The techniques were able to discriminate between various synthesized electrode materials and identify the highly electroactive materials. Preparation variables could be critically evaluated for the synthesis of electrode materials. The techniques were deemed to be applicable in discriminating high and low activity electrode materials based on their structural and chemical properties.
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    Three-dimensional N-doped super-hydrophilic carbon electrodes with porosity tailored by Cu2O template-assisted electrochemical oxidation to improve the performance of electrical double-layer capacitors
    (Royal Society of Chemistry, 2021) Linkov, V; Lv, X; Ji, S
    Three-dimensional (3D), binder-free, porous carbon-based electrodes exhibit high charge storage ability in electrical double-layer capacitors owing to their well-developed porous structures enhancing mass transfer and achieving relatively high electroconductivity. A 3D N-doped carbon electrode with abundant oxygen-containing functional groups was prepared by depositing a PDA-derived N-doped carbon layer and electrochemical oxidation using a porosity-regulatingin situgenerated Cu2O sacrificial template. The optimized electrode demonstrated a high specific capacitance of 2852 mF cm−2at a current density of 1 mA cm−2and good rate capability. The material was used as an electrode in a symmetric capacitor, exhibiting an energy density of 16.4 mW h cm−3at a power density of 180 mW cm−3, which maintained 89% of its value after 15 000 cycles. This study describes a new method of manufacturing high-performance porous electrodes suitable for practical application in electric double-layer capacitors.