Proton diffusivity in protonic ceramic membrane for electrochemical methanation in molten salts

In this study, we characterized the proton diffusivities of perovskite and phosphate in a protonic ceramic membrane at medium temperatures (573‒973 K). The isotropic phonon vibrations of LaGaO₃-based perovskite oxide of La_0.8Sr_0.2Ga_0.8Mg_0.2 O_3‒δ (LSGM) and phosphate of Sn_0.9In_0.1P₂O₇ (SIPO), were evaluated using high-temperature X-ray diffraction measurements. In these ceramic particles, the thermal vibration of oxide ions is the most vigorous among those of consistent ions, confirming that oxide-ion vacancies play a critical role in proton conduction. The isotropic Debye temperatures (Θ_D) were estimated to be Θ_{D, LSGM} = 432 K and Θ_{D, SIPO} = 227 K in air, suggesting that LSGM showed high proton diffusivity. Protonic ceramics tend to have a high proton diffusivity, as confirmed at a high Debye temperature.