Atomic Scale Responses of High Entropy Oxides to Redox\nEnvironments

The\npotential of high entropy oxides (HEOs) as high-performance\nenergy storage materials and catalysts has been mainly understood\nthrough their bulk structures. However, the importance of their surfaces,\nwhich may play an even more critical role, remains largely unknown.\nIn this study, we employed advanced scanning transmission electron\nmicroscopy to investigate the atomic-scale structural and chemical\nresponses of CeYLaHfTiZrO<sub><i>x</i></sub> HEOs to high-temperature\nredox environments. Our observations reveal dynamic elemental and\nstructural reconstructions in the surface of HEOs under different\ngas environments, contrasting with the high stability of the bulk\nstructure. Notably, the surfaces of HEO particles consistently exhibit\nabundant oxygen vacancies, regardless of the redox environment. These\nfindings indicate that HEOs offer distinct advantages in facilitating\nchemical and electrochemical reactions, relying on oxygen vacancies.\nOur results also suggest that the exceptional performance of HEOs\nin energy storage applications arises from surface structural and\nchemical adaptability.