Boosting Photocatalytic Hydrogen Peroxide Production from Oxygen and Water Using a Hafnium-Based Metal–Organic Framework with Missing-Linker Defects and Nickel Single Atoms

Metal–organic frameworks (MOFs) are one of the most promising candidates for photocatalytic hydrogen peroxide (H2O2) production from dioxygen (O2) and water. However, MOF-driven H2O2 production from O2 and water remains a challenge because MOF photocatalysts need to exhibit high structural stability in aqueous reaction systems while suppressing H2O2 decomposition. In the present study, we demonstrate that a Hf-based UiO-66-NH2 with missing-linker defects and Ni single atoms dramatically promotes the photocatalytic production of H2O2 from O2 and water under visible-light (λ > 420 nm) irradiation. The acetate-capped missing-linker defects lead to suppression of the nonradiative relaxation of organic linkers and to the prevention of H2O2 decomposition, whereas the Ni single-atom cocatalysts promote the separation of photogenerated charges and selective two-electron oxidation of water to generate H2O2. The synergetic effect of missing-linker defects and Ni single atoms dramatically improves photocatalytic H2O2 production, resulting in a 6.3-fold increase in activity compared with that of pristine Hf-UiO-66-NH2. This study provides not only new insights into defect engineering in MOF photocatalysts but also an important strategy for achieving highly selective H2O2 production via O2 reduction and water oxidation.