Synergistic Conductivity Effect in a Proton Sources-Coupled Metal–Organic Framework

A water-stable metal–organic framework (MOF)-based composite, H<sub>2</sub>SO<sub>4</sub>@MIL-101-SO<sub>3</sub>H, configured with functionalized sulfonate groups bound to the polymeric backbone and nonvolatile strong acid H<sub>2</sub>SO<sub>4</sub> encapsulated into pores, is demonstrated as a superior proton-conducting material, owing to the resultant multiple proton-transfer pathways. This solid material exhibits a superprotonic conductivity of 1.82 S cm<sup>–1</sup> (70 °C, 90% RH) that is comparable to that of other excellent MOF-based proton conductors reported thus far. More importantly, the splendid conductivity (0.92 × 10<sup>–2</sup> S cm<sup>–1</sup>, −40 °C) of the title material achieves an enormous improvement compared with that of all proton-conducting systems demonstrated at subzero temperatures.