Polyoxometalate Directional Etching for Fabricating Defect Hollow Metal–Organic Framework with Hierarchical Structure

Encapsulating guests in metal-organic frameworks (MOFs) can widely expand their functionality, but usually reduces porosity, hindering reactant and product diffusion. Herein, a simple and rapid room temperature directional etching technique is developed to engineer MOFs with tailored hierarchical structures. With H₃PMo₁₂O₄₀ (PMo₁₂) as an etchant, classical cubic morphology of WNi@Z8, a ZIF-8 MOF encapsulating SiW₁₁NiO₃₉ (WNi), can be transformed into various defect-engineered hollow structures, and a comprehensive phase diagram is established by systematically adjusting etching parameters. Mechanistic studies reveal that PMo₁₂ infiltrates ZIF-8 preferentially through {111} facet, followed by controlled etching along {110} and {100} facets, enabling precise spatial control over cavity formation. The etched WNi@Z8 achieves an exceptional H₂ evolution rate of 12,667 µmol g^-1 h^-1, nearly threefold enhancement over the non-etched counterpart due to the enhanced exposure of encapsulated WNi clusters in the hollow structure. This work provides a generalizable strategy for engineering guest@MOFs to achieve high-efficiency catalysis.