Enhancing p–d hybridization via synergistic regulation of spatial and energetic orbital overlaps in Ba-doped LaNiO₃ epitaxial films for oxygen evolution activity

The hybridization between oxygen 2p and transition-metal 3d states largely determines the electronic structure near the Fermi level and related functionalities of transition-metal oxides (TMOs). Considerable efforts have been made to manipulate the p–d hybridization in TMOs by tailoring the spatial orbital overlap via structural engineering. Here, we demonstrate enhanced p–d hybridization in Ba²⁺-doped LaNiO₃ epitaxial films by simultaneously modifying both the spatial and energetic overlaps between the O-2p and Ni-3d orbitals. Combining x-ray absorption spectroscopy and first-principles calculations, we reveal that the enhanced hybridization stems from the synergistic effects of a reduced charge-transfer energy due to hole injection and an increased spatial orbital overlap due to straightening of Ni–O–Ni bonds. We further show that the enhanced p–d hybridization can be utilized to promote the oxygen evolution activity of LaNiO₃. This work sheds new insights into the fine-tuning of the electronic structures of TMOs for enhanced functionalities.