Two-Dimensional Layer {P4Mo6} Clusters Constructed with N-Ligands for Bifunctional Properties of Proton Conduction and Supercapacitors

Proton exchange membrane fuel cells (PEMFCs) are developing into very meaningful clean energy to fundamentally address environmental pollution. Among which the most studied Nafion series membranes are limited under large-scale use, and some strong oxidizing groups such as hydrogen peroxide will attack the structure of Nafion, shortening the lifespan of PEMFCs. Therefore, it is crucial to develop a proton-conductive material with strong stability and broad application. In this study, a novel hourglass-type P4Mo6-based POMOFs denoted as (H2timb)2[Mn3(H3P4Mo6O31)2]·4H2O was synthesized using 1,3,5-tri(1H-imidazole-1-yl)benzene (timb) as a ligand. It was found that CUST-577 exhibited an excellent proton conductivity of 8.9 × 10-3 S cm-1 at 80 °C and 98% RH (relative humidity), proving that CUST-577 was conducted by protons. In addition, CUST-577 also had a greater H2O2 decomposition ability, thereby improving the longevity of fuel cells. In a three-electrode system, CUST-577 displayed a specific capacitance (Cs) value of 308 F g-1 at a current density of 0.15 A g-1, with a capacitance retention of 88.3% after 2000 cycles. Since the proton-conductive electrolyte can deliver protons for the redox reaction of various pseudocapacitor (PC) electrode materials, CUST-577 may be a promising polyacid-based proton conductor material and PC electrode material.

Anisotropic Single-Crystal Proton Conduction in a Sodium Chain-Based Coordination Polymer

Coordination polymers (CPs) have been identified as promising candidate materials in the field of proton conduction owing to their customizable and diverse structures. However, research on CPs based on alkali metal ions has been less advanced, and the mechanism of proton transport in these materials remains unclear. Herein, a new coordination polymer, [Na2(pytet)(Hdat)2(H2O)3]·2H2O (abbreviated as Na-PyDat) (pytet4- = pyrene-1,3,6,8-tetrasulfonate, dat = 2-hydroxy-4,6-diamino-1,3,5-triazine), has been synthesized based on the starting materials of Na4pytet and 2-chloro-4,6-diamino-1,3,5-triazine, with the latter undergoing in situ transformation to dat under hydrothermal conditions. Na-PyDat is assembled from [Na-O-Na]n double strands and extends to a 3D network through multiple inter- and intrachain hydrogen bonds. Alternate current (AC) impedance analysis shows that Na-PyDat exhibits highly anisotropic single-crystal proton conduction, with a conductivity of 1.04 × 10-4 S cm-1 at 338 K and 90% relative humidity (RH) along the [100] direction, which is 1-2 orders of magnitude higher than those along the [011] and [01̅1] directions, as well as the powder sample under identical conditions. The high proton conductivity along the a-axis direction is closely related to the continuous hydrogen bond chain. To the best of our knowledge, this is one of the few studies reporting single-crystal proton conduction in alkali metal CPs. Moreover, by mixing Na-PyDat with Nafion, the composite membrane presents an enhanced proton conductivity of 4.33 × 10-3 S cm-1 at 338 K and 90% RH, highlighting its potential for future applications in fuel cells.

A Palladium-Containing Polyoxotungstate with Anisotropic Proton Conductivity

Here, a case of bilayer heterojunction Pd-containing polyoxotungstate (POW), connecting a Te3Pd3 ring and an Anderson-like TeW6 cluster, has been synthesized. The Anderson-like cluster is the first example in POW. The coordination of Pd in the ring with the S atom on the sulfo group breaks the traditional coordination configuration of Pd and O in polyoxometalates (POMs), enriching the structural types of Pd-containing POMs. In addition, the hybrid bilayer heterojunction structure at the molecular level not only provides high thermal stability but also results in spatial arrangement anisotropy, leading to up to five times the anisotropic proton conductivity.

Sequential enhancement of proton conductivity by aliovalent cadmium substitution and post-synthetic esterolysis in a carboxylicate-functionalized indium framework with dimethylaminium templates

A sequential improving strategy has devised and implemented on a 3D open framework In-BQ showing 2D intersected channels filled by dimethylamine and its protonated cation constructed by −COOCH3 functionalized anilicate...

Metal hydrogen-bonded organic frameworks: structure and performance

Although great progress has been made in the design, synthesis, and performance expansion of porous materials, new porous materials with stable structures still need to be explored further. In recent years, porous molecular crystals formed by intermolecular interactions have attracted wide attention from chemists, especially metal hydrogen-bonded organic frameworks (M-HOFs) formed by connecting metal complexes through hydrogen bonds. Metal complexes with specific properties (e.g., magnetism, luminescence, sensing, and catalysis) can expand and develop the application of M-HOFs further. However, the huge volume, irregular shape, complex coordination modes, and interference of coordination bonds pose certain challenges in the synthesis and performance expansion of M-HOFs. In this frontier, we summarize the latest progress in the use of 3d, 4d, and 4f metal complexes for the synthesis of M-HOFs, and briefly introduce the performance expansion of these M-HOFs, which is expected to help expand new porous materials with stable structures and specific functions.

Proton conduction studies on four porous and nonporous coordination polymers with different acidities and water uptake

Acidity and water absorption ability are important influencing factors on proton conducting behavior, which are determined by the protonation degree and amount of hydrophilic groups in the crystal structures, respectively.

Proton conductivity studies on five isostructural MOFs with different acidity induced by metal cations

Five isostructural MOFs display very different proton conductivities despite the same proton transfer pathway. This difference is caused by the different coordination ability between the metal cations and the ligand.