Coordination polymer glass from a protic ionic liquid: proton conductivity and mechanical properties as an electrolyte

High proton conducting electrolytes with mechanical moldability are a key material for energy devices. We propose an approach for creating a coordination polymer (CP) glass from a protic ionic liquid for a solid-state anhydrous proton conductor. A protic ionic liquid (dema)(H₂PO₄), with components which also act as bridging ligands, was applied to construct a CP glass (dema)_0.35[Zn(H₂PO₄)_2.35(H₃PO₄)_0.65]. The structural analysis revealed that large Zn-H₂PO₄ ^-/H₃PO₄ coordination networks formed in the CP glass. The network formation results in enhancement of the properties of proton conductivity and viscoelasticity. High anhydrous proton conductivity (<i>σ</i> = 13.3 mS cm^-1 at 120 °C) and a high transport number of the proton (0.94) were achieved by the coordination networks. A fuel cell with this CP glass membrane exhibits a high open-circuit voltage and power density (0.15 W cm^-2) under dry conditions at 120 °C due to the conducting properties and mechanical properties of the CP glass.