Boosting Oxygen Reduction Reaction through Substrate Fluorination-Mediated d-Band Center Tuning and Microenvironment Optimization of Molecular Catalysts

Metal macrocyclic compounds as an electrocatalyst for catalyzing the cathodic oxygen reduction reaction (ORR) in energy conversion devices have been intensively investigated. Promoting the intrinsic ORR activity of catalysts has always been focused on molecular structure design; however, the impact of their loading carbon matrix has been much less explored. In this work, we developed an efficient carbon reconstruction approach to obtain a high level (6.29 at. %) of fluorine-doped carbon substrate (FC), on which poly(iron phthalocyanine) (PFePc) was assembled. The optimized PFePc/FC catalyst composite exhibited efficient activity for ORR in both acidic and alkaline media, achieving a half-wave potential of 0.93 V vs RHE in 0.1 M KOH and 0.74 V in 0.1 M HClO4, respectively. Experimental results and theoretical studies demonstrated that carbon matrix fluorination engineering not only optimized the interfacial hydrophilic/hydrophobic microenvironment but also modulated the d-band center of Fe–N4 sites of the loaded PFePc, thereby reducing the adsorption of oxygen-containing intermediates and promoting its intrinsic ORR activity accordingly. In situ electrochemical impedance spectroscopy (EIS) analysis indicated efficient charge transfer and faster ORR kinetics facilitated by matrix fluorination. This work highlights the advantages of facile substrate fluorination engineering on boosting intrinsic catalytic activity of molecular catalysts for energy conversion applications.