EDTA-enhanced photocatalytic oxygen reduction on K-doped g-C3N4 with N-vacancies for efficient non-sacrificial H2O2 synthesis

Photocatalysis is an emerging approach for H2O2 synthesis through O2 reduction reaction (ORR). However, the ORR is restrained by difficult activation of O2, arising from 1) the weak interaction between photocatalysts (e.g. g-C3N4) and O2, and 2) requirement of a reduction potential negative enough. Here, we describe an EDTA-enhanced ORR for efficient and non-sacrificial H2O2 synthesis on K-doped g-C3N4 with N-vacancies (K-g-C3N4-x). This EDTA/K-g-C3N4-x system delivers an outstanding H2O2 synthesis efficiency with an apparent quantum yield of 27.6 % at 420 nm, exceeding that of the state-of-the-art ORR photocatalysis. This performance can be attributed to the modification of g-C3N4 and introduction of EDTA as a functional molecule. Compared with pristine g-C3N4, the K-g-C3N4-x owns more favorable band structure and richer active sites of N-vacancies for ORR, and significantly improved charge separation efficiency. Moreover, the EDTA could facilitate ORR in thermodynamics and kinetics. Mechanism study demonstrates the key role of carboxylic groups in EDTA, whose interaction with O2 benefits the essential O2 activation process. Notably, the EDTA is a non-sacrificial agent and could stabilize the H2O2 product from decomposition during photocatalysis. This work sheds light on the development of practical photocatalytic approaches for H2O2 synthesis.