Dynamics and Control of Dual Active Sites in Co-Substituted Ni Coordination Polymers for Enhanced Oxygen Evolution Catalysis

Facilitating the kinetically demanding oxygen evolution reaction (OER) is essential for the sustainable conversion of renewable energy into chemical fuels. However, precisely unraveling the dynamics of active species and sites during the OER remains a significant challenge. Herein, we constructed a series of Co-substituted Ni coordination polymers (Ni-CPs) for the OER. Complementary surface-/bulk-sensitive operando time-resolved spectroscopic monitoring enables detailed mechanistic insight into the critical role of partial Co incorporation in modulating the local coordination geometry of Ni centers and thereby promoting the intrinsic OER kinetics. Our results reveal that controlled Co substitution in Ni-CPs facilitates the generation of a substantial fraction of (Ni, Co)(IV) species, which activate O-O bond formation atop the catalytically active Ni^IV-O-Co^IV moieties. These key findings are further supported by kinetic isotopic effect studies and density functional theory calculations, in which the OER in Ni₃Co₁-CPs proceeds via an oxo-radical coupling mechanism, with deprotonation preferentially occurring at the Ni sites. Consequently, the engineered Ni₃Co₁-CPs exhibit enhanced OER activity compared to their oxide counterparts, along with durable electrochemical stability for over 4000 h. This study not only offers detailed mechanistic insights into the dynamics of active species and sites but also highlights their critical role in optimizing the OER kinetics.