Thermodynamics, Transport, and Kinetics in BaZr0.8Y0.2O3−δ Electrolytes and their Impact on Hydrogen Separation and Compression

Abstract

This paper initially fits a comprehensive set of thermodynamic and transport properties charged mobile defects (protons, oxygen vacancies, and small polarons) in proton-conducting BaZr0.8Y0.2O3−δ (BZY20). The fits are based on recently published measurements, including conductivity, proton concentrations via Karl–Fischer titration, and non-stoichiometry via thermogravimetric analysis, all with wide ranges of temperatures and pressures. These properties are needed for inclusion in physics-based models. The paper goes on to fit charge-transfer kinetics in Butler–Volmer form, based primarily in protonic-ceramic fuel cell data in button-cell format. These fits use the previously fitted thermodynamic and transport properties without alteration. The next step is to consider the kinetics of H2O-incorporation kinetics (i.e. Stotz-Wagner hydration). Unfortunately, to date, there are no direct measurements of these thermal (i.e. not charge-transfer) kinetics. However, the present analysis shows great sensitivities to the defect-incorporation kinetics, ranging from near equilibration to strong rate limitations. The paper concludes with modeling and interpreting the performance of an electrochemical hydrogen-compression cell, using the newly established properties.