Enhanced Electron Confinement of p-Block Indium Site in Extended Macrocyclic Conjugation Boosting Oxygen Reduction to Hydrogen Peroxide.

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.