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.