Enhanced Electron Confinement of p-Block Indium Site in Extended Macrocyclic Conjugation Boosting Oxygen Reduction to Hydrogen Peroxide
Yan Xu, Shanyong Chen, Long Chen, Xinwang Zhu, Xiaoqing Qiu, Min Liu
Abstract
The electrocatalytic oxygen reduction reaction via a two-electron pathway (2e – ORR) is a promising route for hydrogen peroxide (H 2 O 2 ) production. However, the strong electron interaction between the metal site and oxygen-containing intermediates usually generates 4-electron ORR, limiting H 2 O 2 selectivity. Here, combining theoretical and experimental studies, we propose to enhance the electron confinement of the indium (In) center in an extended macrocyclic conjugation system toward high-efficiency H 2 O 2 production. The extended macrocyclic conjugation in indium polyphthalocyanine (InPPc) evokes the attenuated transfer electron ability of the In center and weakens the interaction between the s orbital of In and the p obital of OOH*, favoring protonation of OOH* to H 2 O 2 . Experimentally, the prepared InPPc catalyst exhibits a noticeable H 2 O 2 selectivity above 90% in 0.1–0.6 V vs RHE, outperforming the counterpart InPc. Importantly, the InPPc displays a high average H 2 O 2 production rate of 23.77 mg/cm 2 /h in a flow cell. This study proposes a novel strategy to engineer molecular catalysts and provides new insights into the ORR mechanism.