Humidity-sensitive irreversible phase transformation of open-framework zinc phosphate and its water-assisted high proton conduction properties

Open-framework zinc phosphate (NMe₄)(ZnP₂O₈H₃) undergoes irreversible phase transformation. Structural transformation withα(NMe₄·Zn[HPO₄][H₂PO₄] the low-temperature phase) andβ(NMe₄·ZnH₃[PO₄]₂the high-temperature phase) (T_c= 149 °C) and conduction properties were investigated by single-crystal X-ray diffraction, differential scanning calorimetry, and alternating current (ac) impedance. The open-framework material was sensitive to humidity andβproton conductivity was higher than 10⁻²S cm⁻¹at room temperature and 98% relative humidity (RH). Given that the high proton conductivity of the open-framework material can compete with that of many advanced proton conductors based on metal-organic frameworks (MOFs), it has broad application prospects in various electrochemical devices.