Ce‐Induced Differentiated Regulation of Co Sites via Gradient Orbital Coupling for Bifunctional Water‐Splitting Reactions

Abstract Rare‐earth (RE) elements have emerged as crucial promoters to regulate the electrocatalysis of transition metals (TM), but knowledge about the RE‐enhanced mechanism of TM in electrocatalysis is limited. Herein, an array‐like Ce‐CoP catalyst is constructed to explore the origin and distinction of the Ce‐induced enhanced mechanism of Co sites in both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Compared with individual CoP, the developed Ce‐CoP exhibits superior bifunctional electrocatalytic activity with the overpotentials of 81 and 240 mV at 10 mA cm −2 , respectively for HER and OER, with excellent electrocatalytic stability. Theoretical calculations show that the unique 4 f valence electron structure of Ce endows the Co sites with differentiated regulation in the HER and OER through f‐p‐d gradient orbital coupling. In the HER, the retained Ce‐4 f state induces electron spin parallelism at the surrounding Co sites, promoting the adsorption of *H intermediates. While in the OER, the Ce‐4 f band acts as sacrificing band to protect the Co sites from overoxidation through the Ce‐O‐Co chain with an optimized Co‐3 d state, providing additional spin coupling with oxygen intermediates. These findings provide new insights into comprehending the RE‐enhanced mechanism of electrocatalysis and present valuable design guidelines for the development of efficient multi‐functional electrocatalysts.