Ionic Covalent Organic Frameworks-Derived Cobalt Single Atoms and Nanoparticles for Efficient Oxygen Electrocatalysis

Area of Science:

• Materials Science
• Electrochemistry
• Nanotechnology

Background:

• Single-atom metal catalysts offer high activity but suffer from aggregation.
• Controlling metal nanoparticle formation is crucial for optimizing electrocatalysis.
• Covalent organic frameworks (COFs) are explored as precursors for catalyst synthesis.

Purpose of the Study:

• To utilize ionic covalent organic frameworks (iCOFs) as sacrificial precursors to prevent metal aggregation during single-atom catalyst preparation.
• To investigate the influence of iCOFs versus neutral COFs on the resulting catalyst structure and composition.
• To evaluate the electrocatalytic performance of the synthesized catalysts, particularly for oxygen reduction and oxygen evolution reactions.

Main Methods:

• Molecular dynamics simulations to study ion trapping and confinement in iCOFs and COFs.
• Synthesis of cobalt catalysts using iCOFs (CoSA &CoNP-10) and neutral COFs (CoAC &CoNP-25).
• Density functional theory (DFT) calculations to understand catalytic mechanisms.
• Electrochemical testing of catalysts in aqueous and quasi-solid-state zinc-air batteries (ZABs).

Main Results:

• iCOFs effectively trapped and confined more Co ions than neutral COFs, leading to catalysts with single Co atoms and small Co nanoparticles (CoSA &CoNP-10).
• Neutral COFs resulted in catalysts with Co atomic clusters and larger Co nanoparticles (CoAC &CoNP-25).
• CoSA &CoNP-10 exhibited superior oxygen bifunctional electrocatalytic activity compared to CoAC &CoNP-25, consistent with DFT predictions.
• Aqueous ZABs with CoSA &CoNP-10 achieved a power density of 181 mW cm⁻², specific capacity of 811 mAh g⁻¹, and 407 h cycle life.
• Quasi-solid-state ZABs with CoSA &CoNP-10 reached a power density of 179 mW cm⁻² and 30 h cycle life.

Conclusions:

• iCOFs serve as effective sacrificial precursors for synthesizing single-atom cobalt catalysts with enhanced activity by preventing aggregation.
• The resulting CoSA &CoNP-10 catalyst demonstrates excellent bifunctional electrocatalytic performance for oxygen reactions.
• The developed catalysts show significant promise for high-performance aqueous and quasi-solid-state zinc-air batteries.