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.