The complex electrochemical process of oxygen reduction reactions (ORR) poses great challenges to the development of sustainable energy alternatives such as fuel cells and metal-air batteries. The process involves the generation of defect-laden carbon nanoflower (CNF) through the calcination of indium-based metal–organic frameworks (MOFs), which are then functionalized with the molecular catalyst iron phthalocyanine (FePc) to enhance their catalytic performance. The obtained FePc@CNF is featured with a high specific surface area, numerous structural defects, and dispersed FePc molecules, which contributes to the enhanced ORR efficiency. This catalyst demonstrates an impressive onset potential of 0.966 V and a half-wave potential of 0.875 V, as well as a limit current density of 5.616 mA cm−2. Furthermore, it exhibits excellent long-term discharge stability, maintaining a current retention rate of 93.1 % after 20 h, comparable to the state-of-the-art Pt/C. Moreover, the density functional theory calculations reveal that the final step of reducing OH* to H2O and its subsequent desorption is the rate-determining step with a minimum Gibbs free energy of 0.43 eV for FePc@CNF, resulting in an enhanced ORR efficiency.
