Field-Coupled Water Splitting with Metal-Free Donor-Acceptor Covalent Organic-Framework Junctions

Area of Science:

• Materials Science and Engineering
• Electrochemistry
• Catalysis

Background:

• Developing efficient metal-free electrocatalysts for hydrogen and oxygen evolution reactions (HER/OER) is crucial for energy applications.
• Controlling intermediate binding, charge transfer, and mass transport is key to advancing HER/OER performance.
• Existing catalysts often face limitations in acidic and alkaline media, necessitating new design strategies.

Purpose of the Study:

• To design and synthesize novel amide-linked benzene-triazine covalent organic frameworks (BTA/TzTA-Hz COFs) integrated with carbon nanotubes (CNTs).
• To investigate the effect of built-in interfacial electric fields and external magnetic fields on HER/OER performance.
• To elucidate the mechanisms of field-perturbed interfacial charging and magnetohydrodynamic effects on electrocatalytic activity.

Main Methods:

• Synthesis of COF-CNT heterostructures with tailored interfacial properties.
• Density functional theory (DFT) calculations and electrostatic potential mapping to understand active sites.
• Operando electrochemical impedance spectroscopy (EIS), Mott-Schottky analysis, and bubble imaging under varying magnetic fields and biases.

Main Results:

• COF-CNT junctions exhibit complementary active motifs for HER and OER, with CNT integration shifting the contact-potential difference.
• A static magnetic field significantly lowers HER and OER overpotentials by tens of millivolts.
• Field-dependent analysis reveals magnetohydrodynamic convection promoting bubble detachment and mass transport, enhancing catalytic efficiency.

Conclusions:

• Reticular framework chemistry and junction engineering enable programming of reactivity through interfacial electrostatics.
• Built-in and applied fields, including magnetic fields, offer effective strategies to enhance electrocatalyst performance.
• The developed COF-CNT heterostructures represent promising metal-free electrocatalysts for efficient HER and OER.