Stacking Order-Mediated Spin-State Modulation in Iron Phthalocyanine Covalent Organic Frameworks Enables Efficient Oxygen Reduction Reaction

High Resolution Image Download MS PowerPoint Slide Covalent organic frameworks (COFs) such as iron phthalocyanine (FePc) have been considered as potential electrocatalysts. Herein, we provide important insights into modulating the intrinsic activity of FePc COFs for the oxygen reduction reaction (ORR) by adjusting their stacking configuration. The eclipsed, AA-stacked and the staggered, AB-stacked FePc COF configurations were obtained via adjusting the interlayer interaction forces. Electrochemical studies reveal that the AA-stacked FePc COF exhibits a half-wave potential of 0.856 V vs RHE, which is 0.195 V higher than that of the AB-stacked FePc COF. The assembled zinc-air battery, using AA-stacked FePc COF as the cathode, demonstrates a high cell voltage of 1.64 V vs Zn 2+ /Zn alongside with a superior specific capacity of 935.79 mA h –1 g Zn –1 . The upshift in the valence band center and the high effective magnetic moment in the eclipsed, AA-stacked FePc COF suggest that the states are occupied at high energy levels, indicating a high-spin state of Fe. Density functional theory calculations suggest that the long-range spin channels aligned with iron columns in the eclipsed, AA-stacked FePc COF facilitate the spin-selective charge transport through interlayer band dispersion. The mechanism associated with the high-spin state of Fe promotes the cleavage of the *OO and *OOH intermediates, accelerating the ORR kinetics. Our study reveals that the stacking order of FePc COFs is important for modulation of the charge transfer and electron spin states, showing how to control the spin electronic characteristics of COFs through the stacking configuration-dependent interlayer interactions.