Developing cost effective electrocatalysts with high
oxygen evolution reaction (OER) activity is essential for large-scale application of many electrochemical energy systems. Although the impacts of either lattice strain or
oxygen defects on the OER performance of
oxide catalysts have been extensively investigated, the effects of both factors are normally treated separately. In this work, the coupled effects of both strain and
oxygen deficiency on the electrocatalytic activity of La0.7Sr0.3CoO3-δ (LSC) thin films grown on single crystal substrates (LaAlO3 (LAO) and
SrTiO3 (STO)) are investigated. Electrochemical tests show that the OER activities of LSC films are higher under compression than under tension, and are diminished as
oxygen vacancies are introduced by vacuum annealing. Both experimental and computational results indicate that the LSC films under tension (e.g., LSC/STO) have larger
oxygen deficiency than the films under compression (e.g., LSC/LAO), which attribute to smaller
oxygen vacancy formation energy. Such strain-induced excessive
oxygen vacancies in the LSC/STO increases the eg state occupancy and enlarges the energy gap between the O 2p and Co 3d band, resulting in lower OER activity. Understanding the critical role of strain-defect coupling is important for achieving the rational design of highly active and durable catalysts for energy devices.