Turning 2D MOFs into Mixed Ionic-Electronic Conductors via Side Chain Engineering

Area of Science:

• Materials Science
• Chemistry
• Physics

Background:

• Metal-organic frameworks (MOFs) are widely used as electronic or ionic conductors.
• Mixed electron-ion conductivity in MOFs is an underexplored area with significant potential.

Purpose of the Study:

• To develop a new methodology for designing mixed ionic-electronic conductors (MIECs) based on conductive MOFs (cMOFs).
• To orthogonally tune electronic and ionic transport properties through side chain engineering.

Main Methods:

• Synthesized a series of MOFs (M-R) by tethering ethylene glycol (EG) functional groups onto a cMOF core.
• Systematically varied side chain functionalities (nBu, 1EG, 2EG) to modify the pore microenvironment.
• Incorporated LiTFSI salt to evaluate ionic conductivity and measured electronic conductivity.

Main Results:

• Ni-1EG exhibited the highest room-temperature ionic conductivity (1.1 × 10⁻⁴ S/cm), significantly higher than the hydrophobic Ni-nBu.
• Electronic conductivity was preserved in Ni-1EG (∼5 × 10⁻⁴ S/cm).
• Ni-2EG showed reduced ionic conductivity (2.58 × 10⁻⁶ S/cm) likely due to pore blockage, despite increased polarity.

Conclusions:

• Side chain engineering provides a powerful strategy for decoupled control of ionic and electronic transport in cMOFs.
• This work unlocks the potential of cMOFs as tunable platforms for single-phase porous crystalline MIECs.
• The findings open new design possibilities for materials in chemistry, physics, and materials science.