Formation of O2 Dimers in the Perovskite Oxide Electrocatalyst

Renewable energy technologies that employ electrochemical processes necessitates mechanistic understanding of the instability of electrocatalytic materials. The major challenge is the structural degradation of oxide electrodes during electrocatalytic oxygen evolution reaction (OER). Strongly oxidative conditions of the OER are known to induce changes mostly in the surface layer, including amorphization, dissolution, and cation leaching. Here, we show that oxygen intercalation into a perovskite SrCoO3-x electrocatalyst under OER conditions leads to the formation of O2 dimers in its bulk and results in bulk amorphization induced by chemo-mechanical coupling. Specifically, we employ high-resolution resonant inelastic X-ray scattering (RIXS) to unveil the potential-dependent evolution of lattice oxygen in the bulk from the conventional O2- species to quasi-molecular O2 states. Using first principles calculations, we show that oxygen dimers are thermodynamically stable inside the perovskite lattice, providing insight into where and how such dimerization can occur. Ultimately, our study demonstrates that bulk oxygen oxidation is an important process in destabilizing oxide lattice and should be considered in the search for structurally robust OER electrocatalysts.