Defective high-entropy rocksalt oxide with enhanced metal‒oxygen covalency for electrocatalytic oxygen evolution

ABSTRACT High-entropy materials are emerging electrocatalysts by integrating five or more elements into one single crystallographic phase to optimize the electronic structures and geometric environments. Here, a rocksalt-type high-entropy oxide Mg 0.2 Co 0.2 Ni 0.2 Cu 0.2 Zn 0.2 O (HEO) is developed as an electrocatalyst towards the oxygen evolution reaction (OER). The obtained HEO features abundant cation and oxygen vacancies originating from the lattice mismatch of neighboring metal ions, together with enlarged Co/Ni‒O covalency due to the introduction of less electronegative Mg and Zn. As a result, the HEO exhibits superior intrinsic OER activities, delivering a turnover frequency (TOF) 15 and 84 folds that of CoO and NiO at 1.65 V, respectively. This study provides a mechanistic understanding of the enhanced OER on HEO and demonstrates the potential of high-entropy strategy in developing efficient oxygen electrocatalysts by elaborately incorporating low-cost elements with lower electronegativity.