High entropy oxides (HEOs) have been tentatively and prospectively applied for catalysis and energy storage. However, it is hard to further enhance its performance due to the difficult regulation of HEOs' physical-chemical properties. Although some optimized strategies, such as the introduction of noble metal, have been taken to improve the properties and performance of HEOs by a simple and effective way, the current methods could not well guide its commercial preparation and industrial application.
The lamellar CuCoNiZnAl-T-NaOH high entropy oxides with activated Cu, Co, and Ni oxides species accompanied by enhanced lattice oxygen species display improved performance of catalytic redox reactions (CO2 hydrogenation/CO oxidation) and Li-O2 battery. It is unveiled that the easier electron transfer ability over the activated high entropy oxides guarantees its excellent performance. This simple and effective strategy guides the development of creating highly active heterogeneous high entropy oxide catalysts for various functional applications. Image Credit: Chinese Journal of Catalysis
Recently, a research team led by Prof. Zhong-Shuai Wu from State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, reported a general in-situ modulation strategy of solid phase combustion using thiourea addition and alkali liquor treatment to activate metal sites and lattice oxygen species of CuCoNiZnAl HEOs. Consequently, the activated HEOs not only displays higher CO2 hydrogenation and CO oxidation activity, but also owns greatly better electrocatalytic activity (discharge/charge capacities of 12049/9901 mAh/g) with excellent cycle stability (2500 h) on Li-O2 battery than that of pristine HEOs. The results were published in Chinese Journal of Catalysis (DOI: 10.1016/S1872-2067(23)64409-2).
The optimized HEOs using thiourea addition (CuCoNiZnAl-T) and alkali liquor treatment (CuCoNiZnAl-T-NaOH) ones exhibit similar crystal structure with that of CuCoNiZnAl, but higher BET surface area. Meanwhile, the reducibility of CuCoNiZnAl-T-NaOH catalyst is much better than CuCoNiZnAl-T and CuCoNiZnAl. In addition, CuCoNiZnAl and CuCoNiZnAl-T present irregular massive morphology, whereas CuCoNiZnAl-T-NaOH shows sheet-like morphology. Detailly, the CuCoNiZnAl-T-NaOH also possessed more cationic vacancies, distorted lattice and more active lattice oxygen species.
As a result, CuCoNiZnAl-T-NaOH not only shows higher CO2 conversion than that of CuCoNiZnAl and CuCoNiZnAl-T in the temperature range from 350 to 600 °C, but also exhibits higher CO conversion than those of CuCoNiZnAl and CuCoNiZnAl-T in the whole temperature range (especially between 160 and 220 °C). More importantly, CuCoNiZnAl-T-NaOH cathode delivers much higher discharge/charge capacities of 12049/9901 mAh/g than those of CuCoNiZnAl-T (11917/8071 mAh/g) and CuCoNiZnAl (7260/5224 mAh/g) with a stable stability (~2500 h). The excellent performance is mainly attributed to the easier electron transfer between Cu/Ni/Co sites and lattice oxygen species in the framework of CuCoNiZnAl-T-NaOH. Therefore, this present work guides us a novel manner of optimizing HEOs with targeted activated metal sites as highly active heterogeneous thermal and electrochemical catalysts for redox reactions and energy storage through an environment-friendly and cost-effective way.