Conductivities and transport properties of Ca(Zr/Hf)0.9Sc0.1O2.95

Abstract

Doped CaZrO3 proton conductors are promising materials for electrochemical hydrogen sensors, which have already been used in commercialized hydrogen sensors for aluminum melts. Hafnium and Zirconium possess similar properties but their influences on conductive properties of CaZrO3 proton conductors have not been well investigated. In this study, CaZr0.9Sc0.1O2.95 and CaHf0.9Sc0.1O2.95 were prepared by solid-state reaction, and their conductivities and transport properties were systematically investigated by defect equilibria model. Total conductivities of CaZr0.9Sc0.1O2.95 and CaHf0.9Sc0.1O2.95 reached 4.70 × 10−5−1.69 × 10−3 S·cm−1 and 4.83 × 10−6−9.71 × 10−4 S·cm−1 under humid air and 400 °C−800 °C. Their total standard molar hydration enthalpies were estimated to −59.1 kJ/mol and −56.9 kJ/mol, respectively. Conductivities of grain interiors were higher than those of total conductivities, and activation energies of protons were lower than oxide vacancies and holes. Transport numbers showed protonic conduction of Ca(Zr/Hf)0.9Sc0.1O2.95 to always dominate under humid air at 400 °C−700 °C. Protonic transport numbers of CaZr0.9Sc0.1O2.95 and CaHf0.9Sc0.1O2.95 were estimated to 0.41 and 0.44 at 800 °C, respectively. Meanwhile, protonic transport number of grain interiors was higher than that of total sample. Therefore, grain interior could block the transfer of oxide vacancies and holes. In sum, these findings look promising for application on electrochemical hydrogen sensors.