Proton conduction in a new 3-D open-framework vanadoborate with an abundant hydrogen bond system

Abstract

Herein, a novel open-framework vanadoborate, (H₂en)₄H₂[V₁₂B₁₈O₅₄(OH)₆(H₂O)]·11H₂O (1, en = ethylenediamine), was hydrothermally synthesized and structurally characterized. The framework was constructed by discrete [V₁₂B₁₈O₅₄(OH)₆(H₂O)]¹⁰⁻ polyanion clusters with H₂en²⁺ as counterions. An extended network of hydrogen bonds among polyanions, cations, and crystal water molecules links the structure in three dimensions. These structural features endow the present vanadoborate with unique proton conduction properties. This material shows a high proton conductivity of 1.87 × 10⁻⁴ S cm⁻¹ at 333 K under the condition of 100% relative humidity, and the activation energy was estimated to be 0.38 eV.