Mitigating proton trapping in cubic perovskite oxides via ScO₆ octahedral networks

Advances in electrochemical devices have been primarily driven by the discovery and development of electrolyte materials. Yet the development of high-performance and chemically stable proton-conducting oxide electrolytes remains a challenge due to proton trapping and the resulting trade-offs between ionic carrier concentration and conductivity in doped oxides. Here we demonstrate that cubic perovskite oxides with heavy Sc doping can overcome these limitations. BaSn_0.3Sc_0.7O_3-δ and BaTi_0.2Sc_0.8O_3-δ are found to exceed the technological threshold of a total proton conductivity of 0.01 S cm^-1 for fuel cell electrolytes at 300 °C. The structural stability of BaSn_0.3Sc_0.7O_3-δ is further validated under harsh chemical and fuel cell conditions. Molecular dynamics simulations using a machine learning force field illustrate rapid proton diffusion pathways along the ScO₆ octahedral network, effectively mitigating proton trapping, while protons are preferentially associated with Sc. Lattice softness is proposed as a primary design descriptor for increasing Sc content in perovskite oxides and developing high-performance electrolytes for electrochemical devices.