Nitrogen-Shift-Engineered Pt Single-Atom/Cluster Synergy Boosts Covalent Organic Frameworks for Photocatalytic...

Area of Science:

• Materials Science
• Catalysis
• Photochemistry

Background:

• Precise anchoring of metal catalysts onto support sites is crucial for optimizing performance but remains challenging due to surface heterogeneity.
• The influence of local coordination environments on catalyst dispersion and photocatalytic activity is not fully understood.

Purpose of the Study:

• To design isomeric covalent organic frameworks (COFs) with controlled nitrogen-anchoring sites for precise metal catalyst immobilization.
• To investigate the impact of different anchoring sites on platinum (Pt) catalyst dispersion and photocatalytic hydrogen evolution (PHE) performance.

Main Methods:

• Synthesis of four isomeric COFs with identical topologies but distinct N-anchoring sites (imine vs. alkene linkages).
• Immobilization of platinum (Pt) onto the synthesized COFs.
• Photocatalytic hydrogen evolution (PHE) activity testing and apparent quantum efficiency (AQE) measurements.
• Multimodal characterization (e.g., spectroscopy, microscopy) to analyze catalyst speciation and electronic structure.
• Density functional theory (DFT) calculations to elucidate adsorption energies, electron dispersion, and reaction mechanisms.

Main Results:

• Imine-linked COFs demonstrated significantly higher Pt dispersion and superior PHE activity compared to alkene-linked counterparts, with a record rate of 26.72 mmol h⁻¹ g⁻¹.
• The optimal imine-based COF-Pt catalyst achieved an apparent quantum efficiency (AQE) of 12.1% at 420 nm.
• Characterization revealed that imine COFs stabilize dual-active Pt sites (Pt²⁺ and metallic clusters), while alkene COFs primarily host Pt single atoms.
• Synergistic charge transfer between Pt clusters and isolated atoms in imine COFs enhances proton adsorption and reduction kinetics.

Conclusions:

• Constitutional isomerism in COFs provides a powerful platform for decoupling anchoring site geometry from chemical composition, enabling precise control over catalyst immobilization.
• The dual-active site strategy in imine-linked COFs significantly boosts photocatalytic performance through optimized charge transfer and reaction kinetics.
• This study offers fundamental design principles for developing highly efficient and stable atomically precise photocatalyst supports for applications like hydrogen production.