Construction and proton conductivity of a POM-based compound based on different isomers of [Mo8O26]4− ions

Abstract

POM-based material compound 1 with two isomers of [Mo₈O₂₆]⁴⁻ ions, H₂[Cu(α-Mo₈O₂₆)_0.5(β-Mo₈O₂₆)_0.5(L1)₃]·H₂O (L1 = 1,4-bis(imidazole-l-ylmethyl)benzene), has been successfully synthesized. Compound 1 is a crystal containing the {Cu(L1)₄} windmill unit and two [Mo₈O₂₆]⁴⁻ are fixed to the {Cu(L1)₄} unit through hydrogen bonding interactions. Compound 1 is an excellent proton conductor. According to the Nyquist plot of compound 1, at 30 °C, the proton conductivity significantly increases with the increase of the relative humidity. When the relative humidity increases to 90% RH, the proton conductivity is 1.85 × 10⁻³ S cm⁻¹. At 90% RH, as the temperature increases, the resistance decreases and the proton conductivity increases. When the temperature reaches 80 °C, the proton conductivity reaches 1.02 × 10⁻² S cm⁻¹. And according to the calculation of the activation energy, it indicates that the proton conduction process of compound 1 follows the Grotthuss mechanism.