Atomically engineered triphase nanoreactors for selective hydrogen peroxide photogeneration

Overcoming oxygen (O₂) mass transport and active site limitations is key to advancing photocatalytic hydrogen peroxide (H₂O₂) production via the two-electron O₂ reduction reaction (2e⁻ ORR). Here, we design liquid/solid/gas triphase nanoreactors based on Pt single-atom-decorated carbon nitride nanotubes (Pt/CNNT), which synergistically integrate confined O₂ storage, efficient mass transfer, and highly active atomic sites. The hollow nanotube architecture facilitates continuous O₂ delivery, while atomically dispersed Pt sites modulate the electronic structure to enhance O₂ adsorption and *OOH intermediate formation. As a result, the Pt/CNNT nanoreactors exhibit a seven-fold increase in H₂O₂ yield compared to the bulk CN diphase system, reaching 232 μmol g⁻¹ h⁻¹ with apparent quantum yields of 5.1 % and 4.2 % at 400 and 420 nm, respectively. DFT calculations and electrochemical studies confirm the enhanced 2e⁻ ORR selectivity via a sequential two-step 1e⁻ pathway. This work highlights the power of nanoreactor engineering combined with atomic-level catalytic tuning for efficient and selective photocatalytic H₂O₂ synthesis.