Anhydrous Superprotonic Conductivity in the Zirconium Acid Triphosphate ZrH5(PO4)3

The development of solid-state proton conductors with high proton conductivity at low temperature is crucial for the implementation of hydrogen-based technologies for portable and automotive applications. Here, we report on the discovery of a new crystalline tetravalent metal acid triphosphate, ZrH5(PO4)3 (ZP3), which exhibits record-high proton conductivity of 3.0 x 10-2 S cm-1 at 110 °C in anhydrous conditions. Structural characterization and bond-valence sum energy (BVSE) calculations reveal the pathways and mechanism of proton transport. Extended defective hydrogen bond chains, where the protons are dynamically disordered over two oxygen centers, enable fast ionic diffusion with minimal activation energy for proton hopping.