Functional ionic defects, such as oxygen vacancies, in perovskite oxides facilitate catalysis critical for energy storage and conversion devices. However, the deliberate control of oxygen stoichiometry in perovskite-based oxides is challenging due to difficulties in activating these functional oxygen defects at the reduced temperatures required for the low temperature operation of energy storage and generation devices, such as batteries and fuel cells. Here, we use strontium cobaltite (SrCoO_x) “oxygen sponge” to show that epitaxial strain is a powerful tool towards controlling the oxygen vacancy concentration even in highly oxidizing environments, including conditions during the oxygen evolution reaction (OER) that otherwise fully oxidize unstrained SrCoO_x. Our computational approach found that the thermodynamic barrier towards oxygen activation could be lowered by applying a small biaxial tensile strain (~30% with 2% strain). The corresponding change was also experimentally observed, yielding an increasingly oxygen deficient state. The additional oxygen vacancies created by strain artificially enhance the cobaltites’s catalytic activity towards the OER by over an order of magnitude. Our findings demonstrate that strain, rather than simply relying on ambient conditions, can act as the key tuning parameter of oxygen stoichiometry in the next generation of catalytic oxides, functionalizing vacancies for realizing low temperature energy applications.

* This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division (synthesis, theory, and optical and physical property characterization) and by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U. S. Department of Energy (electrochemical characterization).