Demystifying ionic and electronic transport in prominent oxide ion and proton conducting ceramic electrolytes: Ce_0.8Sm_0.2O₂ and BaCe_0.7Zr_0.1Y_0.1Yb_0.1O_3-δ

The development and performance of ceramic electrochemical cells (CECs) depend critically on choosing ceramic electrolytes with optimal ionic and electronic transport properties. In this study, we compare the structural, morphological, and transport characteristics of two representative ceramic electrolytes, oxide ion conducting Ce_0.8Sm_0.2O₂ (SDC) and proton conducting BaCe_0.7Zr_0.1Y_0.1Yb_0.1O_3-δ (BCZYYb). We demonstrate that SDC exhibits higher bulk conductivity but lower open-circuit voltage due to its higher electron density and larger crystallite size. In contrast, BCZYYb possesses higher proton conduction, lower activation energy (0.35–0.38 eV), and higher open-circuit voltage due to its lower electron density and smaller crystallite size with more grain boundaries. BCZYYb shows enhanced proton conductivity in humidified atmospheres due to the hydration of oxygen vacancies, making it more suitable for low-temperature CEC applications. These insights into ceramic electrolyte conduction mechanisms and microstructure-property relationships can guide the optimization of CECs for energy applications.