Enhanced Mass Transfer of Oxygen through a Gas–Liquid–Solid Interface for Photocatalytic Hydrogen Peroxide Production

Solar‐driven photocatalytic oxygen reduction is a potentially sustainable route for the production of hydrogen peroxide (H 2 O 2 ). However, this approach suffers from the limited solubility and slow diffusion of oxygen in water. Another problem is that most photocatalytic oxygen reduction systems do not work well with just water. They often require the addition of sacrificial agents such as alcohols. Here, a covalent organic framework (COF)‐based photocatalyst that can reduce O 2 to H 2 O 2 efficiently in pure water under visible‐light irradiation is reported. A solar‐to‐chemical conversion of 0.76% is achieved for H 2 O 2 generation. More importantly, the hydrophobic and mesoporous properties of triphenylbenzene‐dimethoxyterephthaldehyde‐COF allow the formation of a triphase interface (gas–liquid–solid) when loading this catalyst onto a porous substrate. The H 2 O 2 production rate reaches ≈2.9 mmol g cat −1 h −1 at the triphase interface by overcoming the mass‐transfer limitation of O 2 in water. Notably, this rate is 15 times higher than that in a diphase system (liquid–solid). The photoelectrochemical tests reveal that the increase in yield is closely related to the enhanced mass‐transfer rate and the higher interfacial O 2 concentration. Furthermore, the triphenylbenzene part is identified as the reactive site based on theoretical calculations.