Proton Conduction in Organically Templated 3D Open-Framework Vanadium-Nickel Pyrophosphate

A new proton-conducting material (C₆H₁₄N₂)[NiV₂O₆H₈(P₂O₇)₂]·2H₂O (1) was hydrothermally synthesized by using 1,4-diazabicyclo[2,2,2]octane (DABCO) as the template. Its inorganic framework, determined by single crystal X-ray diffraction, is constructed by the connection of V/NiO₆ octahedral to P₂O₇ pyrophosphate units through sharing oxygen atoms, giving rise to three-dimensional (3D) intersecting 6-, 8-, and 12-ring channels along the [100], [010], and [001] directions, respectively, in which there are ordered protonated DABCO cations balancing negative charge of the framework and disordered water molecules. Complex impedance measurements on polycrystalline samples gave proton conductivities of 4.9 × 10^-3 and 2.0 × 10^-2 S cm^-1 at 25 and 60 °C under high humidity conditions, respectively. The activation energy is 0.38 eV.