High Spin Manganese Boosting Photo-Magnetic Catalytic Hydrogen Evolution Over Covalent Organic Frameworks

Area of Science:

• Materials Science
• Photocatalysis
• Spin Chemistry

Background:

• Electron spin dynamics are underexplored in photocatalysis for hydrogen evolution.
• Conventional diamagnetic photocatalysts have limited response to magnetic fields, hindering spin-dependent carrier dynamics.
• Exploiting spin properties offers a new frontier for enhancing photocatalytic efficiency.

Purpose of the Study:

• To investigate the application of covalent organic frameworks (COFs) in photo-magnetic coupled hydrogen evolution.
• To develop a novel magnetic photocatalyst by incorporating high-spin Mn2+ ions into a COF structure.
• To elucidate the mechanism of spin polarization and magnetic field effects on photocatalytic activity.

Main Methods:

• Post-synthetic metalation strategy to introduce Mn2+ ions into sp2-carbon-linked COF (sp2c-COFdpy).
• Density functional theory (DFT) calculations to determine spin polarization degree at the Fermi level.
• Experimental measurement of photocatalytic hydrogen evolution rates under an external magnetic field (500 mT).

Main Results:

• The resulting sp2c-COFdpy-Mn exhibited intrinsic spin polarization with 100% spin polarization degree at the Fermi level.
• A record photocatalytic hydrogen evolution rate of 208.48 mmol·g-1·h-1 was achieved under a 500 mT magnetic field.
• Mn2+ (3d5 configuration) maximized unpaired electrons, inducing strong spin polarization and a large magnetic moment, enhanced by the external magnetic field.

Conclusions:

• This work establishes the first example of COFs in photo-magnetic catalytic hydrogen evolution.
• The developed spin-engineering strategy provides a pathway for designing high-performance magnetically responsive photocatalysts.
• Synergistic effects of negative magnetoresistance and spin-flip processes under magnetic field suppress recombination and accelerate charge transfer.