Functional Group Effects on the Electrocatalytic Activity of Iron Phthalocyanine for ORR, OER, and HER in Aqueous Medium: Insights from Density Functional Theory

Abstract

This study used density functional theory (DFT) to analyze the ORR, OER, and HER activities of iron-doped phthalocyanine (FePc) functionalized with fluorine (-F), amine (-NH2), and carboxyl (-COOH) groups such as FePc, FePc(F)4, FePc(F)8, FePc(NH2)4, FePc(NH2)8, FePc(COOH)4, and FePc(COOH)8 in solvent medium (water). Structural analyses of the EHOMO-LUMO gaps, XAS spectra, and free energy profiles showed that FePc(COOH)8, FePc(NH2)4, and FePc(NH2)8 were highly favorable for the ORR and HER. FePc and its derivatives exhibit substantial Fe(3d)-N(2p)/C(2p) hybridization near the Fermi level, enhancing the TDOS and providing a more metallic or semi-metallic character than Pc, thereby improving charge transfer for catalytic reactions. The Fe2+ centers on all surfaces have half-filled d6 configurations, which improves their ORR and HER catalytic activity. Carboxyl functionalized structure FePc(COOH)8 has the lowest overpotential for the ORR at 1.16 V compared to the other considered surfaces. In contrast, amine functionalized FePc(NH2)4 and FePc(NH2)8 structures exhibited modest HER overpotentials of -0.01 and -0.08 V, respectively, indicating greater activity towards HER in the solvent phase. Overall FePc(COOH)₈ structure demonstrates excellent bifunctional (ORR/OER) electrocatalytic properties.