Directly observing dynamics at surfaces is critical to understand the material properties that govern energy conversion catalysis. Toward this goal, we have constructed a high harmonic generation light source for ultrafast spectroscopy of surfaces. Using this source, we measure specular reflectance of extreme ultraviolet light from a material at a near-grazing incidence angle. This technique, termed extreme ultraviolet reflection–absorption (XUV-RA) spectroscopy, combines the benefits of X-ray absorption, such as element, oxidation, and spin state specificity, with surface sensitivity and ultrafast time resolution, having a probe depth of only a few nm and an instrument response less than 100 fs. Using XUV-RA spectroscopy, we study the electron dynamics in a number of catalytically relevant metal oxides. CuFeO2 is an earth- abundant photocatalyst, which can reduce CO2 using sunlight. Using XUV-RA spectro- scopy, it is possible to track electrons and holes independently in the Fe 3d, Cu 3d, and O 2p states comprising the band structure of this photocatalyst. Results show that photocatalytic activity is related to ultrafast hole relaxation leading to spatial charge separation in the layered CuFeO2 lattice, which cannot occur in Fe2O3. In a second example, we resolve between two types of defects at the surface of NiO and show that grain boundaries rather than oxygen vacancies are responsible for fast electron-hole pair recombination. This ability to elucidate site-specific charge carrier dynamics in real time provides important criteria for the rational design of catalysts for efficient solar energy harvesting based on their underlying
photophysics.