Highly Conductive and Durable Nb(Ta)-Doped Proton Conductors for Reversible Solid Oxide Cells

Proton-conducting reversible solid oxide cells (P-ReSOCs) are receiving increasing attention because they have potential to efficiently operate at intermediate temperatures to reduce cost and prolong operational life. Here we report our findings in the rational design of a new series of donor- and acceptor-codoped proton conductors through careful manipulation of defect chemistry. Specifically, BaNb(Ta)0.05Ce0.7Yb0.25O3-δ exhibits high ionic conductivity (0.012 S cm–1) while maintaining exceptional stability when exposed to Ar with 30% H2O at 500 °C for 500 h. In contrast, the resistance of BaZr0.1Ce0.7Y0.1Yb0.1O3-δ increases continuously with time under the same condition due to reaction with H2O, as rationalized using density functional theory (DFT)-based computations. In addition, single cells based on BaNb0.05Ce0.7Yb0.25O3-δ achieve a high peak power density of 1.12 W cm–2 in the fuel cell mode and a high current density of 2.24 A cm–2 at 1.3 V in the electrolysis mode at 600 °C. Overall, this work provides new insights for the development of highly conductive and stable proton conductors for P-ReSOCs.