A flexible metal-organic framework with a high density of sulfonic acid sites for proton conduction

The design of stable electrolyte materials with high proton conductivity for use in proton exchange membrane fuel cells remains a challenge. Most of the materials explored have good conductivity at high relative humidity (RH), but significantly decreased conductivity at reduced RH. Here we report a chemically stable and structurally flexible metal-organic framework (MOF), BUT-8(Cr) A, possessing a three-dimensional framework structure with one-dimensional channels, in which high-density sulfonic acid (-SO3H) sites arrange on channel surfaces for proton conduction. We propose that its flexible nature, together with its-SO3H sites, could allow BUT-8(Cr) A to self-adapt its framework under different humid environments to ensure smooth proton conduction pathways mediated by water molecules. Relative to other MOFs, BUT-8(Cr) A not only has a high proton conductivity of 1.27 x 10(-1) S cm(-1) at 100% RH and 80 degrees C but also maintains moderately high proton conductivity at a wide range of RH and temperature.