A Dimolybdenum Paddlewheel Embedded Covalent Organic Framework for Photocatalytic Hydrogen Peroxide Generation

In the midst of the global energy crisis, the conversion of solar energy into chemical energy or high-value chemicals has become critical. Hydrogen peroxide (H₂O₂), a versatile oxidizing agent, plays an important role in chemical synthesis, medical disinfection, and clean energy generation via fuel cells. Recently, photocatalytic H₂O₂ generation from water and oxygen using covalent organic frameworks (COFs) and metal-organic frameworks (MOFs) has emerged as a sustainable approach. In this context, a novel dimolybdenum paddlewheel-embedded COF (Mo-DHTA COF) is presented and synthesized for photocatalytic H₂O₂ generation. It is observed that Mo sites help to bind the oxygen molecule, while high-energy valence band electrons localized on the α-hydroquinone moiety of the COF facilitate efficient photoelectron transfer for oxygen reduction. Simultaneously, the reduced electron density above the hydroxy groups in the conduction band serves as a proton source during H₂O₂ production. Due to these synergistic effects, Mo-DHTA COF exhibited an H₂O₂ production rate of 626 µmol g^-1 h^-1 in aqueous ethanol and 4084 µmol g^-1 h^-1 in aqueous benzyl alcohol, which is found to be higher than the polymeric counterpart of Mo-DHTA (Mo-DHTA-P). This innovative design highlights the potential of metal-embedded crystalline and porous COFs for advanced photocatalytic applications.