Intramolecular Double Activation by Biligands Sharing a Single Metal Atom for Preferred Two-Electron Oxygen Reduction

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• Selective two-electron oxygen reduction reaction (2e-ORR) to produce hydrogen peroxide is challenging.
• Highly active oxygen reduction reaction (ORR) electrocatalysts typically favor the four-electron pathway, reducing oxygen to water.
• Recent theoretical studies suggest the possibility of achieving 2e-ORR preference.

Purpose of the Study:

• To realize preferred 2e-ORR by intramolecular double activation of the peroxide intermediate (*OOH).
• To enhance 2e-ORR selectivity using modified zeolitic imidazolate framework-8 (ZIF-8) catalysts.

Main Methods:

• Utilized zeolitic imidazolate framework-8 (ZIF-8) with imidazole ligands for dioxygen transformation to *OOH.
• Introduced amine groups via ligand exchange to modify ZIF-8 properties.
• Investigated the mechanism of *OOH intermediate activation and desorption.

Main Results:

• Amine decoration on ZIF-8 enhanced 2e-ORR selectivity by 11%.
• The amine group weakened the binding strength of *OOH to the active site via hydrogen bonding (double activation).
• Amine-decorated ZIF-8 achieved 98.5% H2O2 faradaic efficiency at an ultrahigh production rate of 625 mg cm-2 h-1.

Conclusions:

• Intramolecular double activation of *OOH intermediate is an effective strategy for preferred 2e-ORR.
• Amine-functionalized ZIF-8 shows significant potential for efficient hydrogen peroxide production.
• The developed catalyst operates effectively at high rates in a flow cell setup.