Temperature dependence of partial conductivities of the BaZra0.7Ce0.2Y0.1O3-δ proton conductor

Partial conductivities are presented for BaZra(0.7)Ce(0.2)Y(0.1)O(3-delta), an important proton conductor for protonic ceramic fuel cells and membrane reactors. Atmospheric dependencies of impedance performed in humidified and dry O-2, air, N-2 and H-2(10%)/N-2(90%) in the temperature range 300-900 degrees C, supported by the modified emf method, confirm significant electron-hole and protonic contributions to transport. For very reducing and wet atmospheres, the conductivity is predominantly ionic, with a higher participation of protons with decreasing temperature and increasing water-vapour partial pressure (pH(2)O). From moderately reducing conditions of wet N-2 to wet O-2, however, the conductivity is considerably influenced by electron holes as revealed by a significant dependence of total conductivity on oxygen partial pressure (pO(2)). With higher pH(2)O, proton transport increases, with a concomitant decrease of holes and oxygen vacancies. However, the effect of pH(2)O is also influenced by temperature, with a greater protonic contribution at both lower temperature and pO(2). Values of proton transport number t(H) approximate to 0.63 and electronic transport number t(h) approximate to 0.37 are obtained at 600 degrees C for pH(2)O approximate to 0.022 atm and pO(2) approximate to 0.2 atm, whereas t(H) approximate to 0.95 and t(h) approximate to 0.05 for pO(2) approximate to 10(-5) atm. A hydration enthalpy of -109 kJ mol(-1) is obtained in the range 600-900 degrees C. (C) 2017 Elsevier B.V. All rights reserved.