Designing multi-component oxides as air cathode for rechargeable aqueous Zn-air batteries

Date

2024-8-16

Author

Özgür, Çağla

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To address environmental pollution concerns and meet the increasing energy demand, the development of renewable energy systems and cost-effective electrochemical energy storage solutions is essential. Rechargeable zinc-air batteries have gathered significant attention among various energy storage devices due to their high specific energy, cost-effectiveness, and environmental friendliness. However, the sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) during the discharge and recharge process of the air cathode hinder large-scale application. Thus, designing robust and economically viable bifunctional oxygen electrocatalysts is crucial for the commercialization of Zn-air batteries. In this thesis, multicomponent oxide bifunctional electrocatalysts namely high entropy oxides (HEOs) and double perovskite oxides for Zn-air batteries are thoroughly investigated. The effect of oxygen vacancy, porosity, and doping on the electrocatalytic OER/ORR activity and Zn-air battery performance are explored. Firstly, we introduce a novel synthesis method to produce (FeCrCoMnZn)3O4-δ high entropy spinel oxide in a vacuum atmosphere, primarily aimed at incorporating oxygen vacancies into the crystal structure. Compared to its air-synthesized counterpart, the resulting HEO with abundant oxygen vacancies exhibits a better bifunctional index of 0.89 V, indicating enhanced electrocatalytic activity for oxygen reactions. When used as electrocatalysts in the air cathode of Zn-air batteries, the vacuum-synthesized HEO catalysts outperform HEO treated in air, demonstrating superior peak power density, specific capacity, and cycling stability. Then, we applied a low-temperature sol-gel method to synthesize nano-porous (FeCrCoMnZn)3O4-δ powders. To understand the effect of pore size on the electrocatalytic activity, calcination is applied at various temperatures. The HEO powder treated at 600°C exhibits larger pore size and a higher concentration of oxygen vacancies compared to other electrocatalysts calcined at 500°C and 700°C. When used as an air cathode in a Zn-air battery, the HEO treated at 600°C achieves greater capacity and peak power density. Notably, the Zn-air battery with nanoporous HEO treated at 600°C maintains its stability even after 1000 hours of cyclic charge-discharge, demonstrating exceptional stability and durability. Finally, we synthesized B-site doped NdBaCoaFe2aO5+δ (a= 1.0, 1.4, 1.6, 1.8) electrocatalysts to understand the effect of cobalt and iron amount on the B-site of double perovskite oxides. X-ray photoelectron spectroscopy analysis revealed a correlation between iron reduction and increased oxygen vacancy content, which influences the electrocatalyst's bifunctionality by lowering the work function. The electrocatalyst with the highest cobalt content, NdBaCo1.8Fe0.2O5+δ, exhibited a bifunctionality value of 0.95 V, outperforming the other synthesized electrocatalysts. As an air cathode in a Zn-air battery, NdBaCo1.8Fe0.2O5+δ demonstrated superior performance characteristics, including elevated capacity, the highest peak power density, and enhanced durability and stability. Our findings strongly suggest that adjusting the quantity of oxygen vacancies, porosity, and doping of multi-component oxides offers a novel approach to customize electrochemical OER/ORR performance.

Subject Keywords

Zinc-air battery, Oxygen evolution reaction, Oxygen reduction reaction, Perovskite oxide, High entropy oxide

URI

https://hdl.handle.net/11511/110613

Collections

Graduate School of Natural and Applied Sciences, Thesis