Controllable Synthesis and Ultrahigh Proton Conduction of a Hydrogen-Bond Network

The functionalization of polyoxometalates with organic ligands provides a new-style strategy to accurately incorporate polyoxometalates with advanced functional organic moieties on their surfaces, the development of which has attracted increasing research interest due to the potential applications. A germanium tungstate Na₂(H₃O)₆[{Ru^IV(bpy)}₂{WO₂(C₂O₄)}₂(GeW₁₁O₃₉)₂]·27H₂O (bpy = 2,2'-bipyridine) with two ligands covalently modified was triumphantly synthesized, using the conventional one-pot hydrothermal method. It was systematically characterized by thermogravimetric analysis (TGA), elemental analysis, infrared (IR) spectroscopy, single-crystal X-ray diffraction, X-ray photoelectron spectroscopy (XPS), powder diffraction (PXRD), scanning electronic microscopy (SEM), and ultraviolet-visible (UV-vis) spectroscopy. The two-dimensional (2D) layered structure was established through hydrogen bonding and Na⁺ bridges. Impedance measurements indicate that it displays outstanding proton conduction properties, with a splendid conductivity up to 1.24 × 10^-2 S·cm^-1 under 353 K and 90% relative humidity (RH), owing to the rich interlayer hydrogen-bond network formed by the organic ligands ({RuC₁₀H₈N₂}⁴⁺ and {WC₂O₄}⁴⁺), hydrated protons (H₃O⁺), and crystal waters.