Construction of a unique 2-D layered vanadoborate with water-assisted proton conductivity

Abstract

In the present work, a new two-dimensional layered vanadoborate Na₄[V₁₂B₁₈O₅₄(OH)₆(H₂O)]·(H₂en)₄·2(OH)·3H₂O (1, en = ethylenediamine), based on a [V₁₂B₁₈O₅₄(OH)₆(H₂O)]¹⁰⁻ cluster unit, was hydrothermally obtained and characterized. In the structure, the [V₁₂B₁₈O₅₄(OH)₆(H₂O)]¹⁰⁻ clusters are linked by Na⁺ ions into the 2-D layers, which are further connected by water molecules or amine counterions to form 3-D vanadoborate architectures. The guest ions/molecules (i.e., Na⁺, H₂en²⁺, and water) existing in 1 not only act as proton carriers, but also interact with the anions to form a continuous hydrogen-bonding network, thus providing a pathway for proton transport. The abovementioned characteristics make compound 1 an attractive candidate for a proton-conducting material. Complex impedance measurements on crystalline samples gave a proton conductivity of 2.55 × 10⁻⁴ S cm⁻¹ at 333 K and 100% RH, indicating that the compound has a good prospect as a highly efficient proton conductor.