A novel proton conductor of imidazole–aluminium phosphate hybrids in the solid state

Abstract

Anhydrous proton transport at temperatures above 100 °C has attracted considerable attention in the development of fuel cells that operate at intermediate temperatures. Liquid-state imidazole (ImH) is known to be a fast anhydrous proton conductor above 100 °C; however, evaporation and severe conductivity drops above and below its melting point (∼90 °C), respectively, are major drawbacks to ImH. In this paper, we report a novel solid-state anhydrous ImH–Al(H₂PO₄)₃ (AlP) hybrid material prepared via a simple synthesis using mechanical milling. This solid-state hybrid exhibits relatively a high ionic conductivity of ∼0.1 mS cm⁻¹ at 100 °C and remarkably a small activation energy of 0.23 eV. In addition, the ImH–AlP hybrid material provides a means of overcoming both temperature-dependent drawbacks to pure ImH: (1) the ImH–AlP hybrid is thermally stable up to 130 °C, and (2) the hybrid material maintains high ionic conductivity below the melting point of ImH.