Entropy-Assisted B-Site Compositional Engineering in Ruddlesden–Popper La _1.2 Sr _0.8 NiO _4±δ Electrode for Highly Reversible Solid Oxide Cells

Ruddlesden–Popper (RP) oxides are promising oxygen electrodes for solid oxide cells (SOCs); however, their application in reversible SOCs is often limited by polarization-induced lattice instability, Sr segregation, and phase degradation associated with B-site exsolution during SOFC/SOEC cycling. Herein, a B-site high-entropy RP oxide, La1.2Sr0.8(Ni, Fe, Mn, Co, Cr, Cu)O4±δ (LSNO-HEO), is developed to improve structural robustness and operational durability. Multicomponent B-site occupancy perturbs the continuity of the B–O–B framework and increases collective cation-migration barriers, which helps restrain polarization-driven reduction, phase separation, and in situ exsolution under anodic polarization. While increased local compositional disorder may partially weaken long-range electronic transport, the broadened distribution of oxygen-vacancy formation energies is conducive to fast and reversible oxygen exchange kinetics. As a result, the entropy-stabilized RP lattice exhibits reduced Sr segregation and improved electrode/electrolyte interfacial stability during prolonged reversible operation. The LSNO-HEO electrode achieves a peak power density of 2.34 W cm–2 in solid oxide fuel cell (SOFC) mode and an electrolysis current density of 2.56 A cm–2 in solid oxide electrolysis cell (SOEC) mode (under 50% H2O humidified H2 at 1.3 V) at 800 °C, highlighting the entropy-assisted B-site compositional engineering as a sustainable and effective strategy for developing degradation-resistant oxygen electrodes in reversible SOCs.