Unraveling the Contrasting Dynamics of Reconstruction in Wolframite Cobalt Molybdate Polymorphs for Oxygen Evolution Reaction Electrocatalysis

Understanding the dynamic structural evolution of active sites under operating conditions is crucial for designing high-performance electrocatalysts for the oxygen evolution reaction (OER). In this study, we explore the distinct reconstruction behaviors of two cobalt-based molybdate polymorphs, α-CoMoO4 and β-CoMoO4, with wolframite-type structures. α-CoMoO4 undergoes a gradual surface reconstruction, forming amorphous cobalt oxyhydroxide, consistent with the lattice oxygen oxidation mechanism (LOM). In contrast, β-CoMoO4 rapidly transforms into CoOOH through an acid group dissociation (AGD) mechanism involving the dissociation of MoO42– groups. Real-time tracking of the phase transition by cyclic voltammetry (CV) and quick-scanning X-ray absorption fine structure (QXAFS) reveals detailed kinetic insights into these processes. Density functional theory (DFT) calculations attribute the divergent reconstruction pathways to the competition between Co–O and Mo–O bond strengths, with stronger Mo–O bonds facilitating the rapid reconstruction of β-CoMoO4. Notably, surface-sensitive soft X-ray absorption spectroscopy (sXAS) demonstrates that β-CoMoO4 forms a higher concentration of μ2-OH-Co2+/3+ active sites, resulting in its intrinsic activity being 2.1 times that of α-CoMoO4. This work underscores the advantages of AGD-driven reconstruction for generating active sites and provides insights into the rational design of efficient OER electrocatalysts.