Topology-directed spatial confinement and electronic activation of CoO nanoparticles in defect-rich hybrid frameworks for efficient water oxidation

Circumventing the scaling relationship among oxygenated intermediates in the adsorbate evolution mechanism remains a central challenge in oxygen evolution reaction catalysis. Here we report a topology-directed in situ confinement strategy to construct a defect-rich hybrid electrocatalyst comprising ultrafine cobalt oxide (CoO) nanoparticles confined within a nitrogen/sulfur co-doped carbon (NSC) matrix and integrated with reduced graphene oxide (rGO) (CoO@NSC/rGO). This hierarchical architecture suppresses nanoparticle aggregation while providing continuous pathways for charge transfer and mass transport. During oxygen evolution reaction (OER), surface and near-surface regions of CoO function to reconstruct into CoOOH-like oxyhydroxide species that constitute the direct OER-active phase, whereas the residual CoO core acts as a structural and electronic reservoir. Interfacial Co-S/Co-N coordination does not act as an independent active phase but electronically modulates and stabilises the neighbouring CoO-derived CoOOH surface. Spectroscopic analyses and theoretical calculations reveal an electron-enriched Co environment with an upshifted d-band centre, which optimizes the adsorption energetics of oxygen intermediates and facilitates lattice-oxygen participation. lattice oxygen oxidation mechanism (LOM) involvement is further supported by Raman detection of superoxide intermediates and by 18 O-isotope labeling mass spectrometry, which detects 16 O 18 O evolution. Benefiting from these mechanism-enabled kinetics, CoO@NSC/rGO delivers a low OER overpotential and enables efficient overall water splitting at a reduced cell voltage, outperforming commercial IrO 2 under comparable conditions. This work illustrates how topology-confined interfacial electronic modulation can enable LOM-involved OER pathways in Co-based hybrid electrocatalysts.