Fermi Level Equilibration and Charge Transfer at the Exsolved Metal-Oxide Interface

Exsolution is a promising approach for fabricating oxide-supported metal nanocatalysts through redox-driven metal precipitation. A defining feature of exsolved nanocatalysts is their anchored metal-oxide interface, which exhibits exceptional structural stability in (electro)catalysis. However, the electronic interactions at this unique interface remain unclear, despite their known impact on catalytic performance. In this study, we confirm charge transfer between the host oxide and the exsolved metal by demonstrating a two-stage Fermi level (E_F) evolution on SrTi_0.65Fe_0.35O_3-δ (STF) during metallic iron (Fe⁰) exsolution. Combining ambient pressure X-ray photoelectron spectroscopy with theoretical analysis, we show that E_F initially rises due to electron doping from oxygen vacancy formation in STF. Subsequently, upon Fe⁰ precipitation, E_F stabilizes and becomes insensitive to further oxygen release in STF, driven by E_F equilibration and charge transfer between STF and the exsolved Fe⁰. These findings highlight the importance of considering electronic metal-support interactions when optimizing exsolved nanocatalysts.