In-Situ TEM Study of Ba0.5Sr0.5Co0.8Fe0.2O3 for Oxygen Evolution Electrocatalysis

Developing highly active catalysts for oxygen evolution reaction (OER) near room temperature is critical to improve the efficiency of many electrochemical technologies in the pursuit of sustainable energy, such as water splitting using light or electricity, and rechargeable metal-air batteries. Recently, many non-precious metal oxides have been developed as highly active OER catalysts, including many perovskite oxides (ABO₃) of first-row transition metals such as Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF). Previous studies have shown that BSCF has good activity accompanied with surface amorphization in OER process. However, little in-situ study has been done to look into the reasons for its high activity and low stability. In this contribution, we use environmental transmission electron microscopy (ETEM) to investigate the surface atomic structure and chemistry evolution of BSCF in the presence of H₂O. Significant breathing-like structural oscillation has been observed on BSCF, which is closely related to the electron beam and H₂O vapor applied onto the BSCF. Electron energy loss spectra (EELS) implied an electron-beam induced OER on BSCF during breathing motions. This allowed us to observe in-situ BSCF during OER under the TEM, to better understand the incorporation of H₂O into the BSCF structure and the surface amorphization of BSCF in OER process, which might involve the O₂ generation not only on the surface but also in the near-surface layers of BSCF. This work provides a deeper insight into the stability and active site of oxides catalysts for OER.