Inducing the cocktail effect in yolk-shell high-entropy perovskite oxides using an electronic structural design for improved electrochemical applications

High-entropy perovskite oxides (HEPs) are promising for supercapacitors, fuel cells and metal-O2 batteries. However, the obscure mechanism of the cocktail effect makes it challenging to simultaneously enhance the energy storage capability and oxygen reduction reaction. Herein, the cocktail effect is induced through an electronic structural design. Firstly, five non-equimolar elements are optimized in an HEP to achieve strong electron-electron couplings using Bi2+ and Fe2+ as electronic donors and Mn3+ and Cu2+ as electronic acceptors. These couplings form numerous double-exchange interactions for ultralong electron transport chains. Meanwhile, the large bond angle, short bond length, and G-type antiferromagnetic structure achieved in a yolk-shell La0.7Bi0.3Mn0.4Fe0.3Cu0.3O3 HEP lead to optimized electronic structures, which are suitable for accelerating the electron exchange interactions and promoting conductivity. Therefore, the yolk-shell La0.7Bi0.3Mn0.4Fe0.3Cu0.3O3 HEP shows a cocktail effect with the highest catalytic activity toward the oxygen reduction reaction in a 0.1 M KOH electrolyte as well as a substantial specific capacity of 480.95 C g-1 at 0.5 A g-1 in 6 M KOH. Finally, a material design idea for HEPs regulating ions as electronic donors and acceptors is proposed according to Hund's rules to induce a cocktail effect caused by changes in the electronic structures, which is promising for supercapacitors, aqueous fuel cells and metal-O2 batteries.