Enhanced Proton Conduction in Metal-Organic Frameworks through Single-Crystal to Single-Crystal Transformation

Area of Science:

• Materials Science
• Chemistry
• Nanotechnology

Background:

• Metal-organic frameworks (MOFs) are promising materials for various applications.
• Proton conductivity in MOFs is crucial for energy applications like fuel cells.
• Developing MOFs with enhanced proton conductivity remains a challenge.

Purpose of the Study:

• To construct an anionic framework Co-MOF and investigate its proton conductivity.
• To explore the effect of single-crystal-to-single-crystal (SC-SC) transformation on proton conductivity.
• To understand the structure-property relationships governing proton conduction in MOFs.

Main Methods:

• Anionic framework Co-MOF (1) was synthesized.
• SC-SC transformation was induced by immersing (1) in CrCl3 or FeCl3 solutions to form (1-Cr) and (1-Fe).
• Proton conductivity was measured under various humidity and temperature conditions.

Main Results:

• The transformed MOFs (1-Cr and 1-Fe) exhibited significantly enhanced proton conductivities compared to the original MOF (1).
• Proton conductivity of (1-Cr) and (1-Fe) reached 1.49 × 10⁻² and 6.39 × 10⁻³ S cm⁻¹ respectively at 30 °C and 98% RH.
• The enhancement is attributed to the formation of metal-hydroxyl-water clusters and improved proton conduction pathways, leading to lower activation energies (0.12 eV for 1-Cr, 0.18 eV for 1-Fe).

Conclusions:

• SC-SC transformation is an effective strategy to significantly boost proton conductivity in MOFs.
• The introduction of hydroxyl groups via SC-SC transformation facilitates proton conduction pathways.
• This study provides valuable insights for designing advanced MOFs with superior proton conductivity for energy applications.