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 (H2O2). 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 O2 to H2O2 efficiently in pure water under visible‐light irradiation is reported. A solar‐to‐chemical conversion of 0.76% is achieved for H2O2 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 H2O2 production rate reaches ≈2.9 mmol gcat−1 h−1 at the triphase interface by overcoming the mass‐transfer limitation of O2 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 O2 concentration. Furthermore, the triphenylbenzene part is identified as the reactive site based on theoretical calculations. A covalent organic framework (COF) is identified as an efficient photocatalyst for hydrogen peroxide production in pure water by reducing oxygen. The hydrophobic and mesoporous properties of this COF allow the formation of a stable gas–liquid–solid interface and the H2O2 production rate reaches ≈2.9 mmol gcat−1 h−1 at the triphase interface by enhanced oxygen mass transfer.