Intrinsic Superprotonic Conduction in Metal-Free Hydrogen-Bonded Organic-Inorganic Frameworks

Crystalline hybrid networks containing metal coordination centers often disrupt continuous hydrogen-bonding pathways, limiting their intrinsic proton conductivity. Here we report a suite of hydrogen-bonded organic-inorganic frameworks (HOIFs) composed of ionic/neutral organic and metal-free inorganic building units that assemble into two- and three-dimensional hydrogen bonded networks through dense, multidirectional hydrogen bonds. These materials are nonporous and can be classified into three categories based on charge characteristics of their organic and inorganic components. They exhibit a rich structural diversity and unprecedented topologies such as the hoi net in HOIF-101. Systematic investigations show that they possess intrinsic superprotonic conductivity, with most of them achieving conductivity values >10^{- 2} S·cm^{- 1} at 85°C and 100% RH, outperforming their organic counterparts by one to several orders of magnitude and exceeding those of most reported MOFs as well as other metal-free porous frameworks. Comprehensive spectroscopic and computational studies reveal that dynamic inorganic motifs strengthen and modulate extended hydrogen-bond networks and can act as molecular "pumps" to promote Grötthuss-type proton hopping in HOIF-101. Metal-free hybridization thus provides a unique, simple and versatile route to engineer proton mobility and enhance conductivity, expanding the design space for high-performance solid proton conductors with strong potential for diverse applications.