Determination of partial conductivities and computational analysis of the theoretical power density of BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BZCYYb1711) electrolyte under various PCFC conditions

Abstract

High proton conductivity and chemical stability of electrolyte materials are the bottleneck challenges to be overcome for the practical feasibility of protonic ceramic fuel cells (PCFCs). Therefore, the fundamental electrochemical properties of electrolyte materials under cell operating conditions are critical. In this study, the partial conductivities, mobilities, and equilibrium constants of the electrolyte BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3−δ (BZCYYb1711) are determined by a DC four-probe conductivity measurement in the temperature range of 600–750 °C. The electrolyte acts as a proton conductor due to the dominant proton regime with a conductivity of 1.3 × 10⁻² S cm⁻¹ under an air atmosphere (3% H₂O) at 600 °C, whereas mixed-ion conduction appears from 750 °C. The theoretical power densities were calculated from both oxygen ion and proton chemical potential gradient profiles based on the partial conductivities of the mobile charge carriers in the electrolyte. The results show a theoretical peak performance of around 5.28 W cm⁻² for a 10 μm thick electrolyte at 600 °C without considering any electrode polarization. Most importantly, at this temperature, the peak performance of the BZCYYb1711 electrolyte is remarkable, about two times higher than that of conventional oxygen ion conductors, yttrium doped zirconia (YSZ) and gadolinium doped ceria (GDC), as an electrolyte for SOFCs. This indicates that the perovskite proton conductor BZCYYb1711 is an excellent candidate for a protonic fuel cell operated at intermediate temperatures (≤600 °C). Consequently, our work provides performance limits based on the transport properties of the electrolyte as a guideline for the further development of suitable electrode materials for PCFCs.