Structural distortion–driven design of cobalt-free high-entropy perovskite electrodes for high-performance solid oxide cells

High-entropy oxides (HEOs) offer a promising platform for advanced air electrodes in solid oxide electrochemical cells (SOCs), yet the fundamental mechanisms underpinning their enhanced catalytic performance remain elusive. Here, we systematically engineer cobalt-free HEOs of the form (Pr_0.2Bi_0.2Sr_0.2La_0.2X_0.2)MnO_3-δ (X = Ba, Ca, Nd, Gd) by modulating the Goldschmidt tolerance factor to control structural distortion. Fourier electron density analysis reveals distinct octahedral tilting and lattice asymmetry across the series. We uncover a strong correlation between lattice asymmetry, oxygen-ion diffusion characteristics, defect formation, and electrochemical kinetics. Among the compositions, the Nd-substituted variant (PBSLNM) achieves an optimal distortion profile and exhibits outstanding performance, delivering a peak power density of 1.59 W/cm² in fuel cell mode and a current density of 0.73 A/cm² at 1.3 V in electrolysis mode at 700 °C, with excellent durability over 500 h. Density functional theory calculations reveal that structural distortion lowers the oxygen vacancy formation energy, elevates the O 2p band center, and induces heterogeneous electronic distributions that promote both oxygen reduction and evolution reactions. Our findings establish structural distortion as a critical descriptor for HEO performance and provide a rational design strategy for high-performance SOC air electrodes.