Even in ultralow quantities, oxygen vacancies (VO) drastically impact key
properties of metal oxide semiconductors, such as charge transport, surface adsorption,
and reactivity, playing central roles in functional materials performance. Current
methods used to investigate VO often rely on specialized instrumentation under far from
ideal reaction conditions. Hence, the influence of VO generated in situ during catalytic
processes has yet to be probed. In this work, we assess in situ extrinsic surface VO
formation and lifetime under photocatalytic conditions which we compare to
photocatalytic performance. We show for the first time that lifetimes of in situ generated
atomic VO play more significant roles in catalysis than their concentration, with strong
correlations between longer-lived VO and higher photocatalytic activity. Our results
indicate that enhanced photocatalytic efficiency correlates with goldilocks VO
concentrations, where VO densities must be just right to encourage carrier transport
while avoiding charge carrier trapping.