Stacking Order-Mediated Spin-State Modulation in Iron Phthalocyanine Covalent Organic Frameworks Enables Efficient...

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Covalent organic frameworks (COFs) are promising materials for various applications, including catalysis.
• Iron phthalocyanine (FePc) based COFs have shown potential as electrocatalysts.
• Optimizing the electronic and structural properties of FePc COFs is crucial for improving their catalytic activity.

Purpose of the Study:

• To investigate the effect of stacking configuration on the electrocatalytic activity of FePc COFs for the oxygen reduction reaction (ORR).
• To understand the underlying mechanisms responsible for the observed activity differences.
• To demonstrate the potential of tailored FePc COFs in energy storage devices.

Main Methods:

• Synthesis of AA-stacked and AB-stacked FePc COF configurations by tuning interlayer interactions.
• Electrochemical characterization, including cyclic voltammetry and rotating disk electrode measurements.
• Assembly and testing of zinc-air batteries utilizing the synthesized FePc COFs.
• Density functional theory (DFT) calculations to elucidate electronic structure and charge transport mechanisms.

Main Results:

• The AA-stacked FePc COF exhibited a significantly higher half-wave potential (0.856 V vs RHE) for ORR compared to the AB-stacked configuration (0.661 V vs RHE).
• Zinc-air batteries with AA-stacked FePc COF cathodes showed a high cell voltage (1.64 V) and specific capacity (935.79 mA h g^-1).
• DFT calculations revealed that the eclipsed AA-stacking facilitates spin-selective charge transport and promotes ORR kinetics through a high-spin state of Fe.

Conclusions:

• The stacking configuration of FePc COFs critically influences their electronic properties, including spin states and charge transfer.
• Optimizing interlayer interactions to achieve specific stacking orders (e.g., AA-stacking) is an effective strategy to enhance ORR electrocatalysis.
• FePc COFs with controlled stacking offer a promising pathway for developing efficient electrocatalysts for energy conversion and storage applications.