Temperature dependence of partial conductivities of the BaZr 0.7 Ce 0.2 Y 0.1 O 3-δ proton conductor

Abstract

Partial conductivities are presented for BaZr0.7Ce0.2Y0.1O3- an important proton conductor for protonic-ceramic fuel cells and membrane reactors. Atmospheric dependencies of impedance performed in humidified and dry O2, air, N2 and H2(10%)/N2(90%) in the temperature range 300-900 ºC, 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 (pH2O). From moderately reducing conditions of wet N2 to wet O2, however, the conductivity is considerably influenced by electron holes as revealed by a significant dependence of total conductivity on oxygen partial pressure (pO2). With higher pH2O, proton transport increases, with a concomitant decrease of holes and oxygen vacancies. However, the effect of pH2O is also influenced by temperature, with a greater protonic contribution at both lower temperature and pO2. Values of proton transport number tH ≈ 0.63 and electronic transport number th ≈ 0.37 are obtained at 600 ºC for pH2O= 0.022 atm and pO2= 0.2 atm, whereas tH ≈ 0.95 and th ≈ 0.05 for pO2 = 10-5 atm. A hydration enthalpy of-109 kJ.mol-1 is obtained in the range 600-900 ºC.

Gas Humidification Impact on the Properties and Performance of Perovskite‐Type Functional Materials in Proton‐Conducting Solid Oxide Cells

“…Temperature and chemical compositions of the materials and surrounding gas atmospheres determined the individual conductivity, which can be attributed to the bulk transport at temperatures higher than 500–600 °C. According to the profiles of defect concentrations under different conditions (Figure ), the corresponding individual conductivity may predominate under a certain condition ( Figure ):Protonic conductivity predominated under atmospheres with high pH 2 O and low pO 2 levels (wet N 2 , wet H 2 ) at intermediate temperatures.Oxygen‐ionic conductivity predominated under dry reducing atmospheres (dry N 2 , dry H 2 , dry NH 3 ), especially at high temperatures.Hole conductivity predominated in dry oxidizing conditions at elevated temperatures.…”

“…a–d) Protonic, e–h) oxygen‐ionic, and i–l) electron–hole transport numbers as functions of pO 2 and pH 2 O at different temperatures. All panels reproduced with permission . Copyright 2017, Elsevier.…”

Structures, Phase Fields, and Mixed Protonic–Electronic Conductivity of Ba-Deficient, Pr-Substituted BaZr0.7Ce0.2Y0.1O3−δ

“…The development of mixed-conducting protonic-electronic ceramic materials is of considerable interest for a number of high-temperature electrochemical applications involving hydrogen. Barium cerium-zirconate solid solutions with the perovskite (ABO3) structure have emerged as strong candidate materials for electrochemical membranes, with much focus on the composition BaZr0.7Ce0.2Y0.1O3- (BZCY72) 1,2 , which provides both good stability and moderately high proton transport 3 experimented, it is nevertheless apparent that high electron (or electron hole) transport is essential.…”

A Reversible Protonic Ceramic Cell with Symmetrically Designed Pr₂NiO_4+δ-Based Electrodes: Fabrication and Electrochemical Features

“…and, correspondingly, improved proton transport. At the same time, air humidification is considered to be a more effective and easy way of suppressing some of the undesirable electronic conductivity of cerates and zirconates [55,56]. OCVs are not associated with significant electron transport of the electrolytes or imperfect system gas-tightness.…”