Search

A series of metal-free imidazole-benzimidazole catalysts (ImBenz-H, ImBenz-NO 2 , ImBenz-OCH 3 ) for oxygen reduction reaction (ORR) were prepared. We demonstrate that the electrocatalytic O 2 reduction by ImBenz-NO 2 with the electron-withdrawing group showed high selectivity toward H 2 O with the number of electrons transferred (n=3.7) in a neutral aqueous solution. The highest ORR selectivity toward H 2 O 2 was achieved using ImBenz-H (n=2.4) in an alkaline solution. Electrochemical studies of reaction kinetics disclosed that the highest turnover frequencies were obtained from ImBenz-H in both neutral and alkaline aqueous solutions. The results prove that the ORR selectivity is tunable by modulating the substituent of the ImBenz catalysts. Furthermore, DFT calculations suggested that the ORR mechanism of ImBenz-H involves the electron transfer from imidazole-benzimidazole to O 2 resulting in the formation of H 2 O 2 which supports the redox active properties of the catalysts ImBenz., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)