Anomalous photo-thermoelectric effects of platinum-photodeposited tungsten trioxide after gaschromic reaction

Abstract

We attempted to deposit platinum (Pt) onto a tungsten trioxide (WO3) thin film by the photoreduction of Pt4+ (Pt–WO3). Pt on WO3 was oxidized (PtO x) by calcining Pt–WO3 in air to form PtO x–WO3. An n-type anomalous photo-thermoelectric (photo-TE) effect was confirmed for Pt–H yWO3− x, a protonated WO3, after the gaschromic (GC) reaction of Pt–WO3. That is, both the electrical conductivity ( σphoto) and the absolute value of the Seebeck coefficient ( Sphoto) increased under visible-light irradiation. After stopping the irradiation, both values decreased ( σ and S). In contrast, an n-type normal photo-TE effect was observed for PtO x–H yWO3− x after the GC reaction of PtO x–WO3, in which σphoto and the absolute value of Sphoto increased and decreased, respectively, under visible-light irradiation, and vice versa after stopping the irradiation. These findings indicate that Pt was responsible for the generation of the anomalous photo-TE effect, probably due to the electron accumulation capability of Pt, to which electrons were transferred from the conduction band of H yWO3− x. In contrast, electrons could not energetically transfer from H yWO3− x to PtO2, which was included in PtO x particles at the surface. Therefore, PtO x was not responsible for the anomalous photo-TE effect, and PtO x–H yWO3− x behaved like bare H yWO3− x, indicating its normal photo-TE effect.