Phase transition and proton conductivity of CsHSO4-WPA composites prepared by mechanical milling
Abstract A typical solid acid of CsHSO 4 and phosphotungstic acid (H 3 PW 12 O 40 6H 2 O: WPA6H 2 O) were mechanically milled, and non-humidified proton conductivity of the obtained composite was investigated. The 90CsHSO 4 10WPA (mol%) composite showed high proton conductivities of 10 − 2 –10 − 4  S/cm from 160 to 30 °C under dry nitrogen atmosphere, while the conductivity of pure CsHSO 4 dropped abruptly at around 145 °C due to the phase transition from superprotonic CsHSO 4 (I) phase to CsHSO 4 (II) phase. Differential scanning calorimetry (DSC), X-ray diffraction (XRD), and Fourier transform infrared (FT-IR) spectroscopy measurements were performed at various temperatures to study the phase transition behaviour as well as hydrogen bonding structure. The phase transition was not observed for the 90CsHSO 4 10WPA composite. FTIR measurements revealed that a peak for OH stretching shifted to a higher wavenumber with increasing temperature. The O–H•••O hydrogen bond distance was calculated from the OH band wavenumber. The proton conductivities in dry conditions were related to the bonding distance.