In Situ Probing Dynamic Exsolution of Fe⁰ from Perovskite under Graded Potentials

Metal exsolution from perovskite oxides offers a promising approach to developing highly active catalysts. Voltage-driven exsolution achieves a faster rate and better dispersion of the nanoparticles. However, the impact of the external voltage on the dynamic of metal exsolution remains unclear. In this work, we utilized spatially resolved in situ X-ray photoelectron spectroscopy and photoemission electron microscopy to systematically investigate the effect of varied potentials on exsolution within one sample, where spatially graded potentials were applied on a La_0.6Sr_0.4FeO_3-δ electrode. The dynamic characterizations reveal that the exsolution process includes pre-reduction and metal exsolution stages, with exsolution rate and degree modulated by the local surface potential. Potentials more negative than the critical potential at approximately -1.05 V can enhance oxygen vacancy formation and increase the exsolution rate and content of Fe⁰. This work establishes a direct correlation between the local surface potential and exsolution process and highlights the critical role of oxygen vacancies in voltage-driven exsolution.