Scalable Synthesis of Holey Deficient 2D Co/NiO Single‐Crystal Nanomeshes via Topological Transformation for Efficient Photocatalytic CO₂ Reduction

Abstract Preparation of holey, single‐crystal, 2D nanomaterials containing in‐plane nanosized pores is very appealing for the environment and energy‐related applications. Herein, an in situ topological transformation is showcased of 2D layered double hydroxides (LDHs) allows scalable synthesis of holey, single‐crystal 2D transition metal oxides (TMOs) nanomesh of ultrathin thickness. As‐synthesized 2D Co/NiO‐2 nanomesh delivers superior photocatalytic CO₂‐syngas conversion efficiency (i.e., V_CO of 32460 µmol h⁻¹ g⁻¹ CO and of 17840 µmol h⁻¹ g⁻¹ H₂), with V_CO about 7.08 and 2.53 times that of NiO and 2D Co/NiO‐1 nanomesh containing larger pore size, respectively. As revealed in high‐angle annular dark‐field scanning transmission electron microscopy (HAADF‐STEM), the high performance of Co/NiO‐2 nanomesh primarily originates from the edge sites of nanopores, which carry more defect structures (e.g., atomic steps or vacancies) than basal plane for CO₂ adsorption, and from its single‐crystal structure adept at charge transport. Theoretical calculation shows the topological transformation from 2D hydroxide to holey 2D oxide can be achieved, probably since the trace Co dopant induces a lattice distortion and thus a sharp decrease of the dehydration energy of hydroxide precursor. The findings can advance the design of intriguing holey 2D materials with well‐defined geometric and electronic properties.