High pressure study of a new family of superprotonic conductors

Ionic conductors are crucial for a broad range of energy applications, including solid-state batteries and fuel cells. We have recently discovered a new class of metal acid triphosphates, MH5(PO4)3 (M = Ti, Zr, Hf), which exhibit unprecedented anhydrous proton conductivities under ambient conditions. These materials represent a promising new family of superprotonic conductors for next-generation all-solid-state proton batteries. A key limitation in these devices is high interfacial resistance, which can be mitigated through fabrication under high pressure. Understanding the structural response of MH5(PO4)3 compounds to pressure is therefore essential. We propose high-pressure neutron diffraction experiments to map the pressure–temperature space of isostructural TiH5(PO4)3 and ZrH5(PO4)3. Our goals are to investigate pressure-induced changes in hydrogen ordering, identify possible structural phase transitions and assess the influence of pressure on proton transport pathways. TiH5(PO4)3 exhibits a low-temperature transition to a monoclinic phase at 210 K, while ZrH5(PO4)3 retains its trigonal structure to 10 K, potentially suggesting contrasting pressure responses. Measurements will be carried out using the PEARL instrument up to 6 GPa. This study will provide vital insight into pressure-dependent structural mechanisms governing superprotonic conductivity and inform the design of solid-state proton conductors optimised for high-performance, low-resistance energy devices.