Modulating metal-oxygen interactions of high-entropy oxide electrocatalysts enables highly-active and ultra-stable water oxidation

High-entropy oxide (HEO) electrocatalysts are appealing for multi-step catalytic reactions as their high compositional diversity and multi-element synergy effects. Herein, we find that the metal-oxygen (M-O) interactions in FeCoNi-based HEO can be well-optimized by introducing Al and Ce elements. The in-situ electrochemistry-triggered Al leaching exposes abundant newly-formed active sites with greatly reduced energy difference between TM 3d and O 2p orbitals. This fact shows the enhancement of M-O covalency, which is further quantified by the Fe/Co/Ni charge calculations. The stronger M-O covalency greatly decreases the activation energy of water oxidation at Fe/Co/Ni sites and the barrier of electrical transfer. Furthermore, the Ce element downshifts the O 2p band center, effectively refraining lattice oxygen loss. These advantages enable a supersmall overpotential of 303.7 mV at 500 mA cm-2 that maintains 95.8 % even operating for 840 h, which is the best report for the HEOs to date.