Advancing oxygen evolution reaction efficiency in iron phthalocyanines: axial coordination as a key to structural and electronic tuning

Abstract

The decoration of Fe–N₄ sites with axial coordination ligands has been demonstrated as an effective strategy for enhancing their activity in oxygen reduction reactions (ORRs). Such axial ligand effect on oxygen evolution reactions (OERs), however, has not yet been addressed. In the present work, the OER activity of the iron phthalocyanine (FePc) molecule and 15 axial-coordinated FePc derivatives is investigated with first principles calculations. Interestingly, all penta-coordinated FePc outperforms the pristine tetra-coordinated FePc by exhibiting lower overpotentials. Integrated crystal orbital Hamilton population (ICOHP) and partial density of states (PDOS) analyses reveal that the axial coordination can depress the ionic bonding between Fe and OER-relevant intermediates, thereby weakening the adsorption of OER intermediates and enhancing the overall OER activity. Of importance, the activity of FePc–Xs can be qualitatively correlated with the ICOHP of Fe–O bonds, making it a novel and computational cost-effective theoretical descriptor for the structure–activity relationship. Thus, this work not only advances the structure–activity relationship of OER activities of axial-coordinated FePc catalysts, but also provides a general guideline for designing other axial coordinated OER catalysts in the future.