Internal Ligand Substitution Improves External Oxygen Evolution Reaction in Metal Hydroxide-Organic Frameworks

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Engineering coordination defects in catalysts is crucial for enhancing activity while maintaining structural integrity.
• Metal hydroxide-organic frameworks (MHOFs) offer a promising platform for catalyst development.
• Achieving a balance between defect-induced activity and structural stability remains a significant challenge.

Purpose of the Study:

• To develop a novel strategy for defect engineering in MHOFs to simultaneously improve catalytic activity and structural stability.
• To investigate the impact of internal ligand substitution on the electronic structure and catalytic performance of MHOFs.
• To establish a theoretical framework for designing efficient and durable electrocatalysts for water electrolysis.

Main Methods:

• Synthesized Ni-(ABDA)_0.75(BA)_0.25 via internal ligand substitution, replacing 25% of dicarboxylic acid linkers (ABDA) with monocarboxylic benzoic acid (BA).
• Characterized the material's structure, confirming preserved long-range order via π-π stacking and the generation of undercoordinated Ni sites.
• Evaluated the electrocatalytic performance in 0.1 M KOH, measuring overpotential at 1 mA cm^-2.
• Utilized combined experimental and theoretical analyses (e.g., DFT) to understand the mechanism of enhanced catalysis.

Main Results:

• The optimized Ni-(ABDA)_0.75(BA)_0.25 catalyst exhibited a significantly reduced overpotential (326 mV at 1 mA cm^-2), outperforming pristine Ni-ABDA by 122 mV and commercial IrO₂.
• Ligand defects induced electron density redistribution, lowering the thermodynamic barrier for the rate-determining step in the oxygen evolution reaction.
• The tailored electronic structure at undercoordinated Ni sites optimized the adsorption of *O and *OOH intermediates, breaking the scaling relationship.

Conclusions:

• Internal ligand substitution is an effective strategy for defect engineering in MHOFs, enhancing catalytic activity without compromising structural stability.
• The study provides a mechanistic understanding of how undercoordinated metal sites and tailored electronic structures boost electrocatalytic performance.
• This work establishes a pathway for designing highly efficient and durable electrocatalysts for sustainable water electrolysis.