Synthesis and characterization of bifunctional oxygen electrocatalysts for secondary zinc-air batteries

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Kemian tekniikan korkeakoulu | Master's thesis
Functional Materials
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Master's Programme in Chemical, Biochemical and Materials Engineering
In an effort to transition from fossil fuel-based production toward a more sustainable global energy economy, large-scale reforms to the energy infrastructure have been taking place in the past few years. The rapid integration of renewable energy sources in the global energy production scheme, along with the electrification of transport, have created a growing market for battery energy storage to cope with the intermittent nature of renewables. Metal-air batteries have recently gained renewed interest as high-energy density, low-cost, light-weight and environmentally friendly alternatives to the Li-ion batteries currently dominating the market. Among metal-air battery technologies, reversible zinc-air batteries are considered the closest to commercialization. However, the poor performance of bifunctional oxygen electrocatalysts, coupled with large overpotentials during charge/discharge cycles and low cyclability are all obstacles that limit their potential. In this work, two classes of materials, i.e. carbon nanotubes (CNTs) and cobalt-manganese spinel-type oxides were investigated as possible candidates for use as active catalyst layer in the air electrode of reversible zinc-air batteries. The electrocatalytic activity for oxygen evolution (OER) and oxygen reduction (ORR) reactions of the prepared materials was assessed and compared with that of state-of-the-art catalysts (Pt/C and IrO2). In an attempt to better understand the structural origin of the electrocatalytic activity of the materials investigated, common microscopic and spectroscopic characterization techniques (SEM, TEM, Raman, EDX, XRD, XPS) were employed. The results showed promising prospects for the development of efficient and stable bifunctional oxygen electrocatalysts using hybrids of cobalt-manganese spinel oxides and nitrogen-doped CNTs. The performance of these hybrids was generally found to be in good agreement with the results reported in literature on similar materials. New directions for the optimization of the synthetic methods used in this work can be furhter explored in the future in order to enhance the structural and electrocatalytic properties of the synthesized electrocatalysts.
Kallio, Tanja
Thesis advisor
Kauranen, Pertti
secondary zinc-air batteries, bifunctional oxygen electrocatalysts, nitrogen-doped carbon nanotubes, cobalt manganese spinel oxides, oxygen evolution reaction, oxygen reduction reaction
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