Imaging nanoscale photocarrier traps in solar water-splitting catalysts

TL;DR

This paper introduces a novel microscopy technique to directly image nanoscale photocarrier traps in solar water-splitting catalysts, revealing how defects influence photocatalytic efficiency at an atomic level.

Contribution

It develops photomodulated STEM-EELS to map photocarrier localization at the nanoscale, providing direct imaging of defect-induced traps in photocatalysts.

Findings

Direct imaging of oxygen-vacancy trap states in SrTiO3:Rh nanoparticles

Separation of photothermal effects from photocarrier signals

Visualization of defect-induced traps impacting catalytic efficiency

Abstract

Defects trap photocarriers and hinder solar water splitting. The nanoscale photocarrier transport, trapping, and recombination mechanisms are usually inferred from ensemble-averaged measurements and remain elusive. Because an individual high-performing nanoparticle photocatalyst may outperform the ensemble average, design rules that would otherwise enhance catalytic efficiency remain unclear. Here, we introduce photomodulated electron energy-loss spectroscopy (EELS) in an optically coupled scanning transmission electron microscope (STEM) to map photocarrier localization. Using rhodium-doped strontium titanate (SrTiO3:Rh) solar water-splitting nanoparticles, we directly image the carrier densities concentrated at oxygen-vacancy surface trap states. This is achieved by separating photothermal heating from photocarrier populations through experimental and computational analyses of low-loss spectra. Photomodulated STEM-EELS enables angstrom-scale imaging of defect-induced photocarrier traps and their impact on photocatalytic efficiency.