Dual Active Sites in a Single MOF: Achieving High‐Rate and Selective Photocatalytic CO ₂ Reduction to Formate With Concurrent Water Oxidation

A critical challenge in artificial photosynthesis is the limited availability of photocatalysts that effectively integrate active sites for both CO₂ reduction and water oxidation reactions. Herein, we first use defect engineering to integrate the ruthenium 2,2'-bipyridine-6,6'-dicarboxylic acid Ru(bda)³⁺ moiety, renowned for its photosensitivity and water-oxidizing capabilities, into the CO₂-reducing NH₂-UiO-66 framework, that is, d-MOF/Ru. The photoelectrochemical and in situ XPS measurements reveal that the Ru(bda)³⁺ sites fulfill a dual function: enhance visible-light absorption and promote charge separation, while simultaneously serving as active centers for water oxidation. Remarkably, enabled by the concurrent water oxidation activity at the Ru(bda)³⁺ sites, the d-MOF/Ru generates HCOOH at a rate of 2157 µmol gcat. ⁻¹h⁻¹ with 99.7% selectivity under visible light irradiation, a performance 500 times greater than that of pristine NH₂-UiO-66. Furthermore, in situ DRIFTS and theoretical calculations indicate that Zr-oxo clusters promote CO₂ reduction while Ru(bda)³⁺ sites drive water oxidation in a synergistic cycle. This work presents a molecular-level strategy for optimizing photocatalysts, offering new perspectives for improving the efficiency of artificial photosynthesis.