First observation of electrode-correlated protonic conductivity of perovskite-type electrolytes and way towards optimization

Ionic conductivity is usually considered an intrinsic property of an electrolyte, independent of environmental conditions. This study presents, for the first time, evidence that the protonic conductivity of defective perovskite electrolytes is influenced by the electrode performance, based on a comparative study of the conductivity of oxygen-ion-conducting samarium-doped ceria and proton-conducting BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY) using electrochemical impedance spectroscopy (EIS) in a symmetric cell configuration. This contrasts with four different well-known air electrode materials, namely, BaCo_0.7(Ce_0.8Y_0.2)_0.3O_3−δ, La_0.8Sr_0.2MnO₃, BaCo_0.4Fe_0.4Zr_0.1Y_0.1O_3−δ and PrBa_0.5Sr_0.5Co_1.5Fe_0.5O_5+δ, which is further supported using a single cell test. Theoretical considerations and characterization are further taken to understand the different conductivity behaviors of the two electrolytes. The H₂O-temperature-programmed-desorption mass spectroscopy experiment and time-of-flight secondary ion mass spectrometry experiments confirm that the conductivity of the BZCY electrolyte is related to the hydration capability of the electrode materials applied during the test. Drawing upon the finding, the way towards improving both the conductivity of the protonic electrolyte and electrode performance through electrode material tailoring is then proposed. This study provides valuable new perspectives for understanding the conductivity of protonic electrolyte science through concise yet solid material characterization methodologies, which eventually advance the development of protonic ceramic electrolysis/fuel cells for real-world clean energy applications.