Electronic Activation during Nanoparticle Exsolution for Enhanced Activity at Elevated Temperature.

Nanoparticle (NP) exsolution from perovskite-based oxides matrix upon reduction has emerged as an ideal platform for designing highly active catalysts for energy and environmental applications. However, the mechanism of how the material characteristics impacts the activity is still ambiguous. In this work, taking PrSrCoFeNbO thin film as the model system, we demonstrate the critical impact of the exsolution process on the local surface electronic structure. Combining advanced microscopic and spectroscopic techniques, particularly scanning tunneling microscopy/spectroscopy and synchrotron-based near ambient X-ray photoelectron spectroscopy, we find that the band gaps of both the oxide matrix and exsolved NP decrease during exsolution. Such changes are attributed to the defect state within the forbidden band introduced by oxygen vacancies and the charge transfer across the NP/matrix interface. Both the electronic activations of oxide matrix and the exsolved NP phase lead to good electrocatalytic activity toward the fuel oxidation reaction at elevated temperature.