Molecular catalyst of Fe phthalocyanine loaded into In-based MOF-derived defective carbon nanoflowers for oxygen reduction

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.