A water-stable metal–organic framework (MOF)-based composite, H2SO4@MIL-101-SO3H, configured with functionalized sulfonate groups bound to the polymeric backbone and nonvolatile strong acid H2SO4 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–1 (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 × 10–2 S cm–1, −40 °C) of the title material achieves an enormous improvement compared with that of all proton-conducting systems demonstrated at subzero temperatures.

Two-dimensional (2D) conductive metal-organic frameworks (MOFs), whose advanced electrical properties accompany their intrinsic structural characteristics, represent an exciting new class of 2D atomic crystals for the van der Waals integration of novel heterostructures and the development of novel nano/ quantum devices. Guided by topology, we report two 2D MOFs (1 and 2) constructed via combination of [In(COO) 4 ] À metal nodes and tetratopic tetrathiafulvalene (TTF)-based linkers, with ultrahigh proton conductivity (6.66 3 10 À4 and 1.30 3 10 À2 S cm À1 for 1 and 2, respectively). Additionally, high electrical conductivity was simultaneously achieved with the pure protonic nature of the 2D MOF 2. The electrical conduction at the MOF-metal interface is enabled by the redox-switchable behavior of the TTF-based ligands. This unique charge-transport mechanism, protonic/pseudo-capacitance coupling, offers a new strategy for utilizing the ionic conductivity from MOFs to construct functional electronic devices.

The synthesis of hollow opening polyhedral cages has always been an attractive but challenging goal, especially with regard to inorganic polyhedral cages. Herein, we present a novel, 240-nuclearity giant polymolybdate cage prepared via hydrothermal synthesis. This cage is composed of 20 tripod-shaped [Mo6O22(SO3)] n−/[Mo6O21(SO4)] n− building blocks with three connected vertices and 30 cubane-type [Mo4O16] n− edge building blocks, featuring a rare, nearly regular pentagonal dodecahedron with a large inner cavity (diameter up to 1.8 nm) and 12 opening pentagonal windows. This is the highest nuclearity hollow opening dodecahedral cage reported to date. Importantly, this cage exhibits good stability in solution, as revealed by scanning transmission electron microscopy (STEM), TEM, UV–vis, and Raman spectra. In addition, the bulk sample of this compound exhibits an ultrahigh proton conductivity of 1.03 × 10–1 S cm–1 at 80 °C and 98% relative humidity, which is the highest among polyoxometalate-based crystalline proton conductors.

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