Understanding the Electronic Structure Evolution of Epitaxial LaNi_1–<i>x</i>Fe_<i>x</i>O₃ Thin Films for Water Oxidation

Abstract

Rare earth nickelates including LaNiO₃ are promising catalysts for water electrolysis to produce oxygen gas. Recent studies report that Fe substitution for Ni can significantly enhance the oxygen evolution reaction (OER) activity of LaNiO₃. However, the role of Fe in increasing the activity remains ambiguous, with potential origins that are both structural and electronic in nature. On the basis of a series of epitaxial LaNi_1-<i>x</i>Fe_<i>x</i>O₃ thin films synthesized by molecular beam epitaxy, we report that Fe substitution tunes the Ni oxidation state in LaNi_1-<i>x</i>Fe_<i>x</i>O₃ and a volcano-like OER trend is observed, with <i>x</i> = 0.375 being the most active. Spectroscopy and ab initio modeling reveal that high-valent Fe^3+δ cationic species strongly increase the transition-metal (TM) 3d bandwidth via Ni-O-Fe bridges and enhance TM 3d-O 2p hybridization, boosting the OER activity. These studies deepen our understanding of structural and electronic contributions that give rise to enhanced OER activity in perovskite oxides.