New method improves performance of high entropy oxides

High entropy oxides (HEOs) have shown promise for catalysis and energy storage applications, but improving their performance has been challenging due to the difficulty in regulating their physical-chemical properties. While some strategies, like introducing noble metals, have enhanced HEO properties effectively, they have not led to commercial or industrial applications.

Recently, a research team led by Prof. Zhong-Shuai Wu from the State Key Laboratory of Catalysis at the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, reported a new method for in-situ modulation of HEOs using thiourea addition and alkali liquor treatment. This approach activates metal sites and lattice oxygen species in CuCoNiZnAl HEOs through solid phase combustion.

The activated HEOs not only exhibit higher CO2 hydrogenation and CO oxidation activity but also demonstrate improved electrocatalytic performance in Li-O2 batteries, with discharge/charge capacities of 12,049/9,901 mAh/g and excellent cycle stability of 2,500 hours. The research findings were published in the Chinese Journal of Catalysis.

The optimized HEOs, namely CuCoNiZnAl-T (with thiourea addition) and CuCoNiZnAl-T-NaOH (with alkali liquor treatment), possess a similar crystal structure to CuCoNiZnAl but have a higher BET surface area. CuCoNiZnAl-T-NaOH exhibits a sheet-like morphology, in contrast to the irregular massive morphology of CuCoNiZnAl and CuCoNiZnAl-T. Furthermore, CuCoNiZnAl-T-NaOH demonstrates better reducibility and features more cationic vacancies, distorted lattice, and active lattice oxygen species.

Consequently, CuCoNiZnAl-T-NaOH shows superior CO2 and CO conversion compared to CuCoNiZnAl and CuCoNiZnAl-T at various temperatures. Notably, CuCoNiZnAl-T-NaOH delivers significantly higher discharge/charge capacities (12,049/9,901 mAh/g) than CuCoNiZnAl-T (11,917/8,071 mAh/g) and CuCoNiZnAl (7,260/5,224 mAh/g) in Li-O2 batteries, while maintaining stability over approximately 2,500 hours.

The excellent performance of CuCoNiZnAl-T-NaOH can be attributed to the enhanced electron transfer between Cu/Ni/Co sites and lattice oxygen species within the CuCoNiZnAl-T-NaOH framework. This work presents a novel approach to optimize HEOs, enabling the targeted activation of metal sites and creating highly active heterogeneous thermal and electrochemical catalysts for redox reactions and energy storage in an environmentally friendly and cost-effective manner.

Source: Chinese Academy of Sciences

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