Multivariate Sulfonic-Based Titanium Metal-Organic Frameworks as Super-protonic Conductors

Area of Science:

• Materials Science
• Chemistry
• Nanotechnology

Background:

• Proton-conducting materials are crucial for energy applications like fuel cells.
• Metal-organic frameworks (MOFs) offer tunable structures for host-guest chemistry.
• Developing robust and efficient proton conductors remains a significant challenge.

Purpose of the Study:

• To enhance the proton conductivity of a Ti-based MOF (MIP-207) through ligand modification.
• To introduce Brønsted acidic sites using sulfonic acid groups.
• To investigate the proton transfer mechanisms in the modified MOF.

Main Methods:

• Multicomponent ligand replacement strategy using 1,3,5-benzenetricarboxylate (BTC) and 5-SO3H-isophthalate (SO3H-IPA).
• Synthesis of multivariate sulfonic-based solids MIP-207-(SO3H-IPA)x-(BTC)1-x.
• Proton conductivity measurements at various temperatures and humidity levels.
• Ab initio molecular dynamics simulations.

Main Results:

• Successfully tuned proton conductivity of MIP-207 by incorporating sulfonic acid groups.
• Achieved high proton conductivity (σ = 2.6 × 10⁻² S cm⁻¹ at 363 K/95% relative humidity) in the best candidate.
• Simulations confirmed the role of -SO3H groups as proton donors.
• Identified proton transfer via Zundel/hydronium interconversion in a hydrogen-bonded water network.

Conclusions:

• Ligand modification is an effective strategy to enhance MOF proton conductivity.
• The synthesized sulfonic-based MOF demonstrates excellent proton conduction capabilities.
• The study provides insights into the proton transfer mechanism within MOFs.