Preillumination Boosts Photon Utilization Efficiency in CO Oxidation over PtO _<i>x</i> Supported Catalysts

Inefficient photon utilization remains a central challenge in photocatalysis due to rapid charge recombination and the requirement for continuous illumination. In this context, how photons can be more efficiently utilized is an intriguing question, and here we demonstrate an alternative way of photon utilization. In this study, we investigated the preillumination effect on carbon monoxide (CO) oxidation in the following dark period using platinized TiO2 (Pt/TiO2) at ambient temperature and found that CO oxidation was sustained over several hours even after stopping the irradiation. To further optimize the preillumination catalysis, we prepared Pt/TiO2 with modified oxidation states (Ptox/TiO2 and Ptred/TiO2) and compared their CO removal efficiencies in terms of photon utilization. The preillumination of Ptox/TiO2 exhibited a significantly higher apparent quantum efficiency (AQE) for CO oxidation, achieving a 15-fold increase compared to that under continuous irradiation. In contrast, Ptred/TiO2 did not show any preillumination effect. The observed trend of the preillumination effect with varying the Pt oxidation state was entirely opposite to that typically observed in both thermal catalysis and photocatalysis, where Ptred generally exhibited the highest activity. Through electrochemical analyses and in situ infrared spectroscopy, we unveiled the role of Ptox as a reservoir of long-lived electrons (up to several hours), while Ptred facilitated electron transfer to molecular oxygen. The stored electrons activate both lattice O atoms on Ptox and adsorbed molecular oxygen, promoting CO oxidation in a prolonged dark period. Furthermore, the preillumination effect was also observed on Ptox/WO3 under visible light, which implies that this phenomenon can be extended to the removal of indoor CO under room light conditions.