High-Density W Single Atoms in Two-Dimensional Spinel Oxide Break the Structural Integrity for Enhanced Oxygen Evolution Catalysis.

The performance of oxygen evolution reaction (OER) catalysts heavily depends on intrinsically active and robust sites as well as high active site number, which poses challenges in catalyst design concerning composition and structure. This study presents a general oxygen-vacancy anchoring strategy for preparing oxide-based 4d/5d transition metal single-atom 2D materials as efficient and robust OER catalysts. In a typical synthesis, Keggin-structure polyoxometalate [PWO] clusters decompose into tetrahedral WO anions, which in situ adhere to the newly nucleated metal (Co, Fe, Ni) hydroxide (M(OH)) due to the latter's abundant oxygen vacancies, ensuring a uniform distribution of W single atoms. The anchoring of W stabilizes the ultrathin structure, resulting in the annealed W-CoO exhibiting a specific surface area 5-7 times greater than that of pure CoO, even though W has three times the atomic weight of Co. Moreover, the strengthened adsorption of OH induced by W breaks the surface structural integrity of CoO to form a highly active oxyhydroxide, while the increased distortion in Co-O octahedrons further enhances the intrinsic activity. As a result, the catalyst shows a low η of 261 mV in alkaline media, 84 mV lower than that of pure CoO, and an excellent stability of over 290 h. This places it among the best OER catalysts, particularly in comparison to low-activity Ni or -unstable NiFe alternatives.