High Proton Conductivity in Two Stable Bi(III)-Organic Frameworks Based on 2,6-Pyridinedicarboxylic Acid

Area of Science:

• Materials Science
• Chemistry
• Energy Storage

Background:

• Proton-conducting metal-organic frameworks (MOFs) are crucial for energy conversion and storage.
• Bismuth-based MOFs offer low toxicity and versatile coordination chemistry.

Purpose of the Study:

• To synthesize and characterize novel bismuth(III)-based MOFs for proton conduction.
• To investigate the proton transport mechanisms and conductivity of these materials under varying conditions.

Main Methods:

• Hydrothermal synthesis of two bismuth(III) MOFs: [Bi2(Hpdc)2(pdc)2]·2H2O (1) and [pip][Bi(Hpdc)(pdc)]·H2O (2).
• Alternating-current impedance spectroscopy to measure proton conductivity.
• Activation energy analysis to determine proton transport mechanisms.
• Powder X-ray diffraction to confirm structural integrity.

Main Results:

• Both MOFs (1 and 2) exhibit excellent structural, thermal, and water stability.
• Proton conductivity is highly dependent on temperature (30-100 °C) and relative humidity (68%-98% RH).
• Maximum conductivities of 3.38 × 10⁻⁴ S·cm⁻¹ (1) and 0.65 × 10⁻³ S·cm⁻¹ (2) were achieved at 100 °C/98% RH.
• A transition from Vehicle to Grotthuss proton transport mechanisms was observed with increasing humidity.

Conclusions:

• Bismuth-based MOFs are promising candidates for proton-conducting materials.
• The study provides insights into designing MOFs with tunable proton conductivity and mechanism control.
• These findings contribute to the development of next-generation energy systems.