Boosted Charge Transfer for Highly Efficient Photosynthesis of H₂O₂ over Z‐Scheme I⁻/K⁺ Co‐Doped g‐C₃N₄/Metal–Organic‐Frameworks in Pure Water under Visible Light

Abstract

Abstract Photocatalytic oxygen reduction reaction (ORR) is an environmentally friendly and cost‐effective approach for H 2 O 2 synthesis. However, the current photosynthesis system suffers from sluggish kinetics, rapid recombination of photoexcited charge carriers, and weak redox potentials, resulting in unsatisfactory solar‐to‐chemical conversion efficiency. Herein, a Z‐scheme heterojunction (UiO/IKCN) is constructed through coupling I − /K + co‐doped g‐C 3 N 4 (IKCN) with NH 2 ‐UiO‐66, a typical metal‐organic framework material. Under visible light irradiation, the optimal UiO/IKCN exhibits exceptional H 2 O 2 production rates in pure water (13.3 mM g −1 h −1 ) and in isopropanol solution (72.6 mM g −1 h −1 ), that is 48.4 times higher than pristine CN in isopropanol (1.5 mM g −1 h −1 ). A high apparent quantum yield of 10.28% at 420 nm is achieved by UiO/IKCN, surpassing most previously reported values. The dominating role of two‐electron ORR in H 2 O 2 photosynthesis is elucidated in detail. The significantly enhanced photocatalytic activity can be attributed to the facilitated charge separation and Z‐scheme charge transfer, which are unambiguously verified by stable‐state surface photovoltage, transient photoluminescence, femtosecond transient absorption spectroscopy, in‐situ irradiated X‐ray photoelectron spectroscopy, and density functional theory calculations. This study represents the first exploration of H 2 O 2 production using NH 2 ‐UiO‐66 and provides insights into the rational design of Z‐scheme heterojunction for highly efficient photosynthesis.