Designing UiO-66-Based Superprotonic Conductor with the Highest Metal-Organic Framework Based Proton Conductivity

Area of Science:

• Materials Science
• Chemistry
• Nanotechnology

Background:

• Metal-organic frameworks (MOFs) are increasingly important as proton conductors.
• UiO-66-based MOFs offer a promising platform for proton conduction applications.
• Post-synthetic modification is a viable strategy to tune MOF properties.

Purpose of the Study:

• To design and synthesize two post-synthetically modified UiO-66 MOFs with varying side-arm lengths.
• To investigate the impact of side-arm length on the proton conductivity of these MOFs.
• To understand the proton conduction mechanism in MOF-based materials.

Main Methods:

• Post-synthetic modification of UiO-66-NH2 using sultones to introduce -SO3H groups.
• Synthesis of two homologous compounds, PSM 1 and PSM 2, with different alkyl chain lengths.
• Measurement of proton conductivity and activation energy at various temperatures.
• Theoretical analysis including molecular electrostatic potential and NBO analysis.

Main Results:

• PSM 1, with a shorter alkyl chain, exhibited exceptional proton conductivity (1.64 × 10^-1 S cm^-1) at 80 °C, surpassing commercial Nafion.
• PSM 2, with a longer alkyl chain, showed significantly lower proton conductivity (4.6 × 10^-3 S cm^-1).
• PSM 1 demonstrated one of the lowest activation energies for proton conduction among MOF-based materials, while PSM 2 required nearly three times higher energy.

Conclusions:

• The length of the side arm in post-synthetically modified MOFs profoundly influences proton conductivity.
• Even a single carbon difference in side-arm length can lead to orders-of-magnitude changes in conductivity.
• These findings provide crucial insights for designing highly efficient MOF-based proton conductors.