Pivotal Role of Interfacial Strain in Ultrathin Nickelate Oxide Films for Cost-Effective Oxygen Evolution Reaction

Cost-efficient perovskite oxides have been widely studied as non-noble-metal catalysts due to their tunable structures and electronic properties. However, polycrystal perovskites consist of dissimilar surface morphologies, randomly distributed structural defects, and crystallographic planes, which inevitably complicates the understanding of electrocatalytic mechanisms. Herein, single-crystal LaNiO₃ thin films were studied as a model system to modulate oxygen evolution reaction (OER) performance by synergistically controlling the interfacial strain and film thickness. Our results demonstrate a 3-fold increase in the level of the OER performance achieved by imposing substantial compressive strain exceeding -2.0% on 3 nm-thick epitaxial LaNiO₃ films, compared to that of bulk counterparts. Combined experiments and calculations reveal that compressive strain promotes the occupation of the <i>d</i>_<i>z</i>^<i>2</i> orbital, weakening the adsorption energy of OH^- intermediates and concomitantly enhancing the OER performance in the LaNiO₃ ultrathin films through the lattice oxygen mechanism. These findings open up rich playgrounds for rational design of cost-effective electrocatalytic oxide ultrathin films.