Linkage Microenvironment and Oxygen Electroreduction Reaction Performance Correlationship of Iron Phthalocyanine-based Polymers.

Iron phthalocyanine-based conjugated polymers (PFePc) offer well-defined sites, rendering them ideal model systems to elucidate structure-property relationships towards oxygen reduction reaction (ORR), but have struggled to achieve improved catalytic activity due to uniform electron distribution of iron center and difficulty in molecular-level structure design. Although rationally linkage microenvironmental regulation is an effective approach to adjusting activity, the underlying fundamental mechanism is incompletely understood. Herein, systematic DFT calculations and experimental investigation of PFePc analogous reveal that the incorporation of the electron-withdrawing benzophenone linkage into the PFePc backbone (PFePc-3) drives the delocalization of Fe d-orbital electrons, downshifts the d-band energy level, thereby tailoring the key OH* intermediate interaction, demonstrating enhanced ORR performance with a half-wave potential of 0.91 V, a high mass activity of 21.43 A g-1, and a high turnover frequency of 2.18 e s-1 site-1. Magnetic susceptibility measurements and electron paramagnetic resonance spectroscopy reveal that linkage regulation can induce a 3d electron with high spin-state (t2g 3eg 2) of PFePc-3, significantly accelerating the ORR kinetics. In situ scanning electrochemical microscopy and variable-frequency square wave voltammetry further highlight the rapid kinetics of PFePc-3 to the high accessible site density (6.14×1019 site g-1) and fast electron outbound propagation mechanism.