Preillumination Boosts Photon Utilization Efficiency in CO Oxidation over PtO x 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 TiO 2 (Pt/TiO 2 ) 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/TiO 2 with modified oxidation states (Pt ox /TiO 2 and Pt red /TiO 2 ) and compared their CO removal efficiencies in terms of photon utilization. The preillumination of Pt ox /TiO 2 exhibited a significantly higher apparent quantum efficiency (AQE) for CO oxidation, achieving a 15-fold increase compared to that under continuous irradiation. In contrast, Pt red /TiO 2 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 Pt red generally exhibited the highest activity. Through electrochemical analyses and in situ infrared spectroscopy, we unveiled the role of Pt ox as a reservoir of long-lived electrons (up to several hours), while Pt red facilitated electron transfer to molecular oxygen. The stored electrons activate both lattice O atoms on Pt ox and adsorbed molecular oxygen, promoting CO oxidation in a prolonged dark period. Furthermore, the preillumination effect was also observed on Pt ox /WO 3 under visible light, which implies that this phenomenon can be extended to the removal of indoor CO under room light conditions.