Dual-site La/Ni substitution stabilizes cubic perovskite SrCoO_3-δ for efficient oxygen evolution

SrCoO_3-δ has been widely regarded as a promising electrocatalyst for the oxygen evolution reaction (OER) owing to its superior structural tunability and compositional flexibility. However, the cubic perovskite (CP) phase of SrCoO_3-δ is difficult to stabilize under ambient pressure, and single-site substitution is insufficient to simultaneously stabilize the CP framework and optimize the B-site active centers. Herein, a series of La_xSr_1-xCo_1-xNi_xO_3-δ (x = 0, 0.05, 0.1, 0.15, 0.2) (L_xSCN_xO) catalysts was synthesized by the sol-gel method. La/Ni dual-site substitution drove a phase transformation from hexagonal H-SCO (P6₃/mmc) to a single-phase cubic perovskite CP-L_xSCN_xO (x = 0.1, 0.15; Pm3̄m), whereas L_0.2SCN_0.2O was predominantly cubic with a trace SrLaCoO₄ impurity. This structural evolution concurrently enhanced active-site exposure and established a favorable B-site Co/Ni mixed-valence-oxygen-defect coupling state, thereby improving the OER activity. Among the series, CP-L_0.1SCN_0.1O exhibits the best OER performance with an overpotential (η₁₀) of 336 mV at 10 mA cm^-2 in 1 M KOH (409 mV for H-SCO), which further decreases by 45 mV after 1000 CV cycles. While facilitating the exposure of active sites, La and Ni co-doping reduces the effective average oxidation state of the B site from +3.44 (Co⁴⁺/Co³⁺ ≈ 0.802) to +3.20 (Co⁴⁺/Co³⁺ ≈ 0.536), establishing a favorable Co/Ni mixed-valence state. The resulting CP phase facilitates the generation of oxygen vacancies and highly oxidative oxygen species (O₂^2-/O^-), as well as the formation of the active CoOOH phase during the OER process, significantly promoting OER kinetics. This study reveals the critical role of La and Ni co-doping in stabilizing the CP structure, optimizing the B-site elemental environment, and promoting surface reconstruction, offering new insights for the rational design of efficient CP-SrCoO_3-δ-based OER catalysts.