STRUCTURE-PERFORMANCE CORRELATION IN ROCK-SALT AND SPINEL HIGH ENTROPY OXIDES FOR OXYGEN ELECTROCATALYSIS AND PSEUDOCAPACITIVE ENERGY STORAGE

Date

2025-9-1

Author

Coşkuner, Ali Burçay

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Electrochemical energy materials are increasingly important for enabling clean energy conversion and storage. Depending on the process mechanism, these materials can function as either electrocatalysts or electrodes. A clear understanding of their structural characteristics is essential for tailoring electrochemical behavior and achieving high-performance devices. In this study, the influence of crystal structure on the oxygen electrocatalysis and capacitive electrode performance of high-entropy oxides (HEOs) was investigated. Two HEOs with distinct crystal structures, rock-salt (HRS) and spinel cubic (HSP), were synthesized. For the oxygen evolution reaction (OER), the overpotentials at a current density of 10 mA cm⁻² were 311 mV for HRS and 357 mV for HSP. In zinc–air battery (ZnAB) testing, the HRS-based cell sustained stable operation for nearly 180 h, while the HSP-based cell lost stability after about 60 h. This stability difference is likely related to the microstrain in addition to the configurational entropy, which is expected to be higher in HRS. Williamson–Hall analysis confirmed that HRS likely exhibits significantly greater inhomogeneous lattice strain than HSP when cationic sites are occupied by Ni, Co, Cr, Cu, and Al, reflecting structural differences. In capacitive performance tests, specific capacities at 0.5 A g⁻¹ were 307 F g⁻¹ for HRS and 166 F g⁻¹ for HSP. Electrochemical analysis further revealed that HRS behaves as a pseudocapacitive electrode, whereas HSP displays characteristics of a battery-type electrode.

Subject Keywords

High Entropy Oxide, Crystal Structure, Electrocatalysis, Zinc-air Battery, Supercapacitor

URI

https://hdl.handle.net/11511/116080

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Graduate School of Natural and Applied Sciences, Thesis