Structural modulation of metal-organic framework glasses for alkali metal ion transport and conduction

Abstract

Metal-organic framework (MOF) glasses have distinguished themselves as an emerging class of amorphous coordination materials that combine the chemical tunability of MOFs with the processability of glassy solids. Unlike crystalline MOFs, where ion migration is dominated by periodic pore architectures, ion conduction in MOF glasses is expected to arise from the interplay among disordered coordination networks, sub-nanometer free volume, dynamic metal-ligand interactions, and macroscopically grain-boundary-free monolithic structures. This review discusses the structural regulation of MOF glasses for alkali-metal-ion transport, with emphasis on coordination-environment modulation, free-volume control, glass-transition dynamics, and interface-mediated transport. We further highlight the importance of electrochemical and structural characterization, including humidity-dependent impedance spectroscopy, isotope effects, pair distribution function (PDF), extended X-ray absorption fine structure (EXAFS), and positron annihilation lifetime spectroscopy (PALS), to establish reliable structure-transport relationships. We outline future opportunities for MOF-glass ion conductors in anhydrous proton electrolytes, solid-state batteries, ion-selective membranes, and integrated energy devices, calling for a transition from empirical materials discovery to predictable and device-oriented ion-channel design.