How Strontium Titanate Nanoparticles' Atomic Surface Termination and Excited-State Carrier Distributions Influence their Photoactivity

In this work, we study doped, cocatalyzed STO nanoparticles using ultrafast and atomic-resolution scanning TEM (STEM) spectroscopies to relate their structural/electronic properties and photoactivity. Water-splitting nanoparticle bed reactors offer a promising pathway to renewably generate hydrogen. However, STO nanoparticles have not yet reached external quantum efficiencies needed for commercial viability – even optimized catalysts produce an order of magnitude less hydrogen than predicted by thermodynamic efficiency estimates. We spatially resolve STO's photocarrier lifetimes and excited-state carrier distributions using correlative STEM cathodoluminescence and photomodulated EELS. We then compare the photoactivity of STO with Sr-O and Ti-O surface termination as measured with STEM-EELS. We use an excited-state approach to density functional theory and the Bethe-Salpeter equation to model thermal and carrier effects on the low- and core-loss EEL spectra under an adiabatic approximation. These results advance the field of ultrafast TEM-EELS and inform optimal STO photocatalyst synthetic methods.