Understanding the Electronic Structure Evolution of Epitaxial LaNi<sub>1–<i>x</i></sub>Fe<sub><i>x</i></sub>O<sub>3</sub> Thin Films for Water Oxidation
Le Wang, Prajwal Adiga, Jiali Zhao, Widitha S. Samarakoon, Kelsey A. Stoerzinger, Steven R. Spurgeon, Bethany E. Matthews, Mark Bowden, Peter V. Sushko, Tiffany C. Kaspar, George E. Sterbinsky, Steve M. Heald, Han Wang, Linda Wangoh, Jinpeng Wu, Er‐Jia Guo, Haijie Qian, Jiaou Wang, Tamás Varga, Suntharampillai Thevuthasan, Zhenxing Feng, Wanli Yang, Yingge Du, Scott A. Chambers
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 LaNi1–xFexO3 thin films synthesized by molecular beam epitaxy, we report that Fe substitution tunes the Ni oxidation state in LaNi1–xFexO3 and a volcano-like OER trend is observed, with x = 0.375 being the most active. Spectroscopy and ab initio modeling reveal that high-valent Fe3+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.