Elucidation of a Photothermal Energy Conversion Mechanism in Hydrogenated Molybdenum Suboxide: Interplay of Trapped Charges and Their Dielectric Interactions

Hydrogenated molybdenum suboxide (HxMoO3-y) is a promising photo -thermal energy conversion (PEC) material. However, its charge carrier dynamics and underlying mechanisms remain unclear. Utilizing flash-photolysis time-resolved microwave conductivity, we investigated charge carrier-dielectric interactions in the Pt/HxMoO3-y composite. The charge recombination of H2-reduced Pt/HxMoO3-y was 2-3 orders of magnitude faster than that of Pt/MoO3, indicating efficient PEC. A complex photo-conductivity study revealed that Pt/HxMoO3-y has two types of trapping mechanisms, Drude-Zener (DZ) and negative permittivity effect (NPE) modes, depending on the reduction temperature. Pt/HxMoO3-y reduced at 100 degrees C exhibited a dominant NPE owing to the electrical interaction of trapped charges with the surrounding ions and/or OH base. This polaronic trapped state retarded the PEC process. We found Pt/HxMoO3-y reduced at 200 degrees C to be optimal owing to the balanced suppression of the NPE and charge diffusion. This is the first report revealing the charge dynamics in hydrogenated metal oxides and their impacts on PEC processes.

Automated summary

Hydrogenated molybdenum suboxide (HxMoO3-y) is a promising material for photo-thermal energy conversion (PEC), but its charge carrier dynamics and mechanisms are not well understood. In this study, charge carrier-dielectric interactions in Pt/HxMoO3-y composite were investigated using flash-photolysis time-resolved microwave conductivity. The results showed that the charge recombination of H2-reduced Pt/HxMoO3-y was much faster than that of Pt/MoO3, indicating efficient PEC. The study also identified two trapping mechanisms, Drude-Zener (DZ) and negative permittivity effect (NPE) modes, in Pt/HxMoO3-y depending on the reduction temperature. Optimal PEC performance was achieved when Pt/HxMoO3-y was reduced at 200 degrees C, balancing the suppression of NPE and charge diffusion. This study provides the first insights into charge dynamics in hydrogenated metal oxides and their impact on PEC processes.