Engineering Oxygen Vacancies in (FeCrCoMnZn)3O4-δ High Entropy Spinel Oxides Through Altering Fabrication Atmosphere for High-Performance Rechargeable Zinc-Air Batteries.

High entropy oxides (HEOs) offer great potential as catalysts for oxygen electrocatalytic reactions in alkaline environments. Herein, a novel synthesis approach to prepare (FeCrCoMnZn)3O4-δ high entropy spinel oxide in a vacuum atmosphere, with the primary objective of introducing oxygen vacancies into the crystal structure, is presented. As compared to the air-synthesized counterpart, the (FeCrCoMnZn)3O4-δ with abundant oxygen vacancies demonstrates a low (better) bifunctional (BI) index of 0.89 V in alkaline media, indicating enhanced electrocatalytic oxygen catalytic activity. Importantly, (FeCrCoMnZn)3O4-δ demonstrates outstanding long-term electrochemical and structural stability. When utilized as electrocatalysts in the air cathode of Zn-air batteries, the vacuum atmosphere synthesized (FeCrCoMnZn)3O4-δ catalysts outperform the samples treated in an air atmosphere, displaying superior peak power density, specific capacity, and cycling stability. These findings provide compelling evidence that manipulating the synthesis atmosphere of multi-component oxides can serve as a novel approach to tailor their electrochemical performance.

Facile Synthesis and Origin of Enhanced Electrochemical Oxygen Evolution Reaction Performance of 2H-Hexagonal Ba2CoMnO6-δ as a New Member in Double Perovskite Oxides.

Perovskite oxides have been considered promising oxygen evolution reaction (OER) electrocatalysts due to their high intrinsic activity. Yet, their poor long-term electrochemical and structural stability is still controversial. In this work, we apply an A-site management strategy to tune the activity and stability of a new hexagonal double perovskite oxide. We synthesized the previously inaccessible 2H-Ba2CoMnO6-δ (BCM) perovskite oxide via the universal sol-gel method followed by a novel air-quench method. The new 2H-BCM perovskite oxide exhibits outstanding OER activity with an overpotential of 288 mV at 10 mA cm-2 and excellent long-term stability without segregation or structural change. To understand the origin of outstanding OER performance of BCM, we substitute divalent Ba with trivalent La at the A-site and investigate crystal and electronic structure change. Fermi level and valence band analysis presents a decline in the work function with the Ba amount, suggesting a structure-oxygen vacancy-work function-activity relationship for Ba x La2-x CoMnO6-δ (x = 0, 0.5, 1, 1.5, 2) electrocatalysts. Our work suggests a novel production strategy to explore the single-phase new structures and develop enhanced OER catalysts.