Proton-Conducting Phenolate-Based Zr Metal–Organic Framework: A Joint Experimental–Modeling Investigation

The proton-conduction performances of the chemically stable porous zirconium phenolate MIL-163 MOF were characterized for the first time by complex impedance spectroscopy. Whereas this large square-shaped channel-like MOF exhibits very poor conductivity under anhydrous conditions, measurements performed at 90 °C and 95% relative humidity evidenced a superprotonic behavior with a conductivity of 2.1 × 10 –3 S·cm –1, among the highest values reported so far for water-stable MOFs. This experimental investigation was further supported by Monte Carlo simulations to shed light on the effects of both the guest molecules (i.e., dimethylamine and water) and the acidic protons from the constitutive inorganic chains on the conduction properties of this porous hybrid solid. It was found that the water molecules form a three-dimensional hydrogen-bond network leading to the formation of multiple pathways that bridge the acidic Zr-bonded phenol groups of the organic linker, which act as a proton source. The dimethylamine molecules were revealed to form single hydrogen bonds with H 2 O without leading to a disruption of the water hydrogen-bond network. This offers an optimal situation for the water-mediated transfer of protons over long distances at the origin of the good proton-conducting performance of MIL-163.