Phase transition and proton conductivity of CsHSO 4–WPA composites prepared by mechanical milling

Abstract

A typical solid acid of CsHSO 4 and phosphotungstic acid (H 3PW 12O 406H 2O: WPA6H 2O) were mechanically milled, and non-humidified proton conductivity of the obtained composite was investigated. The 90CsHSO 410WPA (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 410WPA 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.