Dual Type‐II Heterojunction Coupled With Superoxide Radical Conversion Enables Efficient Solar‐Driven H ₂ O ₂ Synthesis in Seawater

ABSTRACT Photocatalysis enables green H 2 O 2 synthesis using water and oxygen as feedstocks, yet its efficiency is limited by rapid photogenerated electron–hole recombination and sluggish superoxide radical (O 2 · − ) conversion to H 2 O 2 . This study presents the Mn SAC @PDA‐CdS photocatalyst, featuring a dual type‐II heterojunction coupled with O 2 · − conversion, for efficient H 2 O 2 production via modifying cadmium sulfide nanorods (CdS) with manganese single‐atom‐doped polydopamine (Mn SAC @PDA). The doping of Mn SAC introduces an intermediate energy level (Mn‐DE) above the valence band (VB) of PDA, creating an additional interfacial hole transfer pathway from CdS to VB of PDA. Upon illumination, photogenerated holes in the VB of CdS migrate to both the VB of PDA and the Mn‐DE. This dual type‐II heterojunction effectively suppresses electron–hole recombination, promoting the migration of more photoelectrons from PDA to the CB of CdS. Consequently, the generation of O 2 · − via electron‐driven O 2 reduction and the supply of protons via hole‐driven H 2 O oxidation can be facilitated. Moreover, PDA coating accelerates the conversion of O 2 · − to H 2 O 2 by boosting proton and electron transfer via switching between catechol and o‐benzoquinone states. As a result, Mn SAC @PDA‐CdS achieves H 2 O 2 production rate of 4806 µmol·L −1 ·h −1 in seawater without any sacrificial agents, surpassing most reported systems.