Hydrogen‐Bonded Organic Frameworks (HOFs): A New Class of Porous Crystalline Proton‐Conducting Materials

Abstract

Two porous hydrogen‐bonded organic frameworks (HOFs) based on arene sulfonates and guanidinium ions are reported. As a result of the presence of ionic backbones appended with protonic source, the compounds exhibit ultra‐high proton conduction values (σ) 0.75× 10−2 S cm−1 and 1.8×10−2 S cm−1 under humidified conditions. Also, they have very low activation energy values and the highest proton conductivity at ambient conditions (low humidity and at moderate temperature) among porous crystalline materials, such as metal–organic frameworks (MOFs) and covalent organic frameworks (COFs). These values are not only comparable to the conventionally used proton exchange membranes, such as Nafion used in fuel cell technologies, but is also the highest value reported in organic‐based porous architectures. Notably, this report inaugurates the usage of crystalline hydrogen‐bonded porous organic frameworks as solid‐state proton conducting materials.

Facile crystallization of 2-phenyl benzimidazole-5-sulfonic acid: Characterization of lattice water dependent zwitterionic supramolecular forms, with modulation in proton conductivities

“…Crystalline non-covalent organic frameworks, [1][2][3][4][5][6] parallel to those of metal-organic frameworks, 7 have attracted a great deal of interest in the recent literature, owing to their intriguing and complementary structural possibilities and functional characteristics. Particularly, the materials, which are stable under aqueous environments, possessing Lewis acidic charge carriers, with extensive hydrogen bonded networks in their structures, are expected to be functional alternates 8,9 for fluorinated ionomers, like Nafion, 8,9 for fuel cell applications, and thus are being investigated for their proton transport characteristics.…”

“…Particularly, the materials, which are stable under aqueous environments, possessing Lewis acidic charge carriers, with extensive hydrogen bonded networks in their structures, are expected to be functional alternates 8,9 for fluorinated ionomers, like Nafion, 8,9 for fuel cell applications, and thus are being investigated for their proton transport characteristics. [2][3][4][5][7][8][9][10][11][12] The inherent advantages of crystalline frameworks, such as wide scope for intuitive designs, accurate structure determinations, possibility of loading different guests within the frameworks, etc., have fueled the scope of such materials as proton electrolytes in the academic research. [2][3][4][5][7][8][9][10][11][12] Recently we also have reported the proton transporting performances of some simple, easily accessible, and environmentally benign coordination polymers to highlight the relevance of biomimetic materials in this perspective.…”

Self-Recognizing π-π Stacking Interactions Designed for the Generation of Ultrastable Mesoporous Hydrogen-Bonded Organic Frameworks

“…Recently, hydrogen-bonded organic frameworks (HOFs), [1][2][3][4] self-assembled from pre-designed molecular tectons using intermolecular H-bonding interactions, are rapidly expanding into a library of novel functional crystalline porous materials with diverse structures and applications including gas storage and separation, 5,6 chiral separation, 7 chemical sensing, 8 proton conduction, 9 and catalysis. 10,11 However, since the first report of HOF materials with permanent microporosity about a decade ago, 12 the development of HOFs has been hindered due to poor stability as a result of the weak H-bonding nature.…”

Self-Recognizing π-π Stacking Interactions Designed for the Generation of Ultrastable Mesoporous Hydrogen-Bonded Organic Frameworks

“…Recently, hydrogen-bonded organic frameworks (HOFs), [1][2][3][4] self-assembled from pre-designed molecular tectons using intermolecular H-bonding interactions, are rapidly expanding into a library of novel functional crystalline porous materials with diverse structures and applications including gas storage and separation, 5,6 chiral separation, 7 chemical sensing, 8 proton conduction, 9 and catalysis. 10,11 However, since the first report of HOF materials with permanent microporosity about a decade ago, 12 the development of HOFs has been hindered due to poor stability as a result of the weak H-bonding nature.…”