Remarkably high proton conductivity in cubic perovskite-related Ba3WO6

Abstract

The Ba₃WO₆ material was reported to have seven kinds of polymorphs. However, the crystal structures of most of them were not established. In this work, the polymorph (denoted as α-Ba₃WO₆ hereafter) with a cubic 4 × 4 × 4 superstructure of a simple perovskite structure was prepared, with its crystal structure being solved by combining powder X-ray diffraction (XRD) and neutron powder diffraction (NPD) techniques. This structure showed intrinsically severe barium- and oxygen-deficiencies. Variable temperature XRD revealed a phase unstable region within 600–1000 °C. The electrical property study on α-Ba₃WO₆ revealed extremely high proton conductivities at temperatures below 600 °C, e.g. 1.75 × 10⁻² S cm⁻¹ at 500 °C, which is comparable to that of the BaCeO₃-based materials. A fuel cell based on α-Ba₃WO₆ electrolyte yielded a power density of ∼520 mW at a working temperature of 500 °C. The α-Ba₃WO₆ material thus shows great potential for being used as an electrolyte for proton conducting fuel cells (PCFCs). This work thus may further stimulate the development of superior proton conductors in oxides with a superstructure of the simple perovskite structure.