Defect-Driven Evolution of Oxo-Coordinated Cobalt Active Sites with Rapid Structural Transformation for Efficient Water Oxidation.

Reconstructing the surface nature of metal-organic frameworks (MOFs) as precatalytic structures is a promising methodology for improving electrocatalytic performance. However, regulating the structural evolution of MOFs during electrolysis remains highly uncontrollable and lacks an in-depth understanding of the role of in situ -derived active sites. Here, we suggest a simple approach to fine-tune the symmetry of Co-MOFs with an oxo-coordinated asymmetric coordination that acts as a prototypical structure motif for the oxygen evolution reaction (OER). Through a facile thermal treatment, the Co-N4 configuration of Co-MOFs transforms to the distorted Co-N3-oxo configuration of defective Co-ligand nanoclusters. By operando spectroscopic characterization, the reconstructed Co-N3-oxo structure enables a rapid structural transition toward homogeneous oxyhydroxides. Moreover, the defective nature of the precatalytic structure regulates the surface Co-O bonding environment with abundant μ ₂ -O-Co ³⁺ sites, thereby exhibiting highly enhanced OER activity with an overpotential of 256 mV at 10 mA cm ^-2 and excellent durability for 100 h, compared with the pristine Co-MOFs. Atomistic simulations reveal that the effect of OER intermediates on the oxyhydroxides gets distributed among neighboring Co ions, promoting balanced binding of the intermediates. This work highlights an effective strategy to design the MOF-based structure for optimizing the surface nature, thus enhancing the electrocatalytic activity.