Water splitting at imine-linked covalent organic frameworks.

Area of Science:

• Materials Science
• Catalysis
• Computational Chemistry

Background:

• Covalent organic frameworks (COFs) are versatile metal-free catalysts.
• Imine-linked COFs with donor (D) and acceptor (A) groups offer tunable functionality.
• Understanding structure-property relationships is crucial for optimizing COF catalysts.

Purpose of the Study:

• Systematically investigate the electronic and catalytic properties of D/A imine-linked COFs.
• Analyze the influence of protonation, constitutional isomerism, and solvation on COF performance.
• Elucidate the origins of differing catalytic rates in related experimental studies.

Main Methods:

• Density functional theory (DFT) calculations were employed.
• Water splitting was used as a model reaction system.
• Protonation effects, constitutional isomerism (DNCA vs. DCNA), and solvation were analyzed.

Main Results:

• Protonation of COFs was found to decrease their band gap.
• COFs with donor groups closer to the imine nitrogen (DNCA) exhibit lower band gaps than DCNA isomers.
• Reaction energies for hydrogen and oxygen evolution were similar across isomers, but charge distribution differed.

Conclusions:

• Constitutional isomerism in D/A COFs influences charge distribution.
• Differences in charge distribution are proposed as a key factor for observed variations in hydrogen evolution rates.
• DFT provides valuable insights into the catalytic mechanisms of COFs for water splitting.