Distinguishing Bulk and Grain Boundary Transport of a Proton-Conducting Electrolyte by Combining Equivalent Circuit Scheme and Distribution of Relaxation Times Analyses

Features of ionic transport across grains and along grain boundaries of solid oxide electrolyte materials play a key role in the efficient application of these materials in electrochemical devices including solid oxide fuel and electrolysis cells, membrane reactors, and electrochemical converters. In the present work, equivalent circuit scheme (ECS) and distribution of relaxation times (DRT) analyses were successfully utilized to distinguish the bulk and grain boundary resistances, both from each other and from the polarization resistance component. Considering a Ag|BCG|Ag symmetrical cell (where BCG = BaCe0.9Gd0.1O3−δ) as a simple model system, the complex impedance spectra were obtained. Due to the close characteristic parameters (relaxation time and capacitance) exhibited by some electrochemical processes, these spectra cannot be precisely resolved using only an ECS tool, although a joint application of ECS and DRT allowed the spectra to be deconvoluted. As a result, data concerning grain and grain boundary conductivities were obtained along with their activation energies. The good agreement of these data with those published in the literature indicates the correctness of the provided analysis. The presented results confirm the wide applicability of ECS/DRT for various electrochemical functions.