Tuning Electronic Properties of Copper-Doped La _0.8 Sr _0.2 Fe _{0.4– <i>x</i>} Cu _<i>x</i> Co _0.4 Al _0.2 O _3−δ for Enhanced Oxygen Ion Migration for High-Temperature Hydrog

High-temperature hydrogen production using solid oxide electrolysis cells (SOECs) and two-step thermochemical water splitting (STWS) relies on oxides that combine high oxygen mobility with strong structural integrity. Here, the potential of La0.8Sr0.2Fe0.4–xCuxCo0.4Al0.2O3−δ (where x = 0, 0.1) perovskites via experimental and computational methods is reported. The main results confirm that the incorporation of Cu leads to lattice contraction, enhanced oxygen release, an increase in the O 2p band center by 0.33 eV, and a reduction in the Co–O charge transfer energy from 1.39 to 1.11 eV. These modifications boost the O 2p–TM 3d covalency, decrease the oxygen ionicity, and shift the redox activity from Fe toward Co and Cu. Density functional theory (GGA+U) calculations reveal a nearly 48% decrease in the vacancy formation energy (from 2.20 to 1.15 eV) and lower migration barriers at 0.19 eV due to local O–M–O distortions. Surface studies show molecular adsorption on Co at −0.58 eV and dissociative adsorption on Fe and Cu at −2.77 and −2.45 eV, respectively. Oxygen vacancies reduce the H2 production reaction energy to 1.97 eV on Cu, which highlights that doping represents a very good strategy to improve the performance of the investigated material, offering valuable insights for mixed-conductor design in sustainable hydrogen production.