Supplemental Material for
Photo- and gas-tuned, reversible thermoelectric properties and anomalous photothermoelectric effects of platinum-loaded tungsten trioxide
Kenta Suzuki,1 Takuya Watanabe,1 Hirofumi Kakemoto,2 and Hiroshi Irie2,a)
1
Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, 4-3-11
Takeda, Kofu, Yamanashi 400-8511, Japan
2
Clean Energy Research Center, University of Yamanashi, 4-3-11 Takeda, Kofu, Yamanashi 4008511, Japan
a)
Author to whom correspondence should be addressed; electronic mail: [email protected]
Contents
S. 1
S. 2
S. 3
S. 4
SEM images (Fig. S1).
Back reaction of Pt/WO3 and WO3 in the presence and absence of O2 (Fig. S2).
Power factor, PF (Fig. S3).
Schematic diagram of Pt/WO3 (Fig. S4).
1
S. 1
SEM images (Fig. S1)
Figures S1a and S1b show SEM images of WO3 and Figs. S1c and S1d show those of Pt/WO3. The film
thicknesses of Pt/WO3 and WO3 were ~500 nm and ~700 nm, respectively. Pt/WO3 had greater surface roughness
than WO3. These differences are attributed to the differences in viscosity of the precursor solution with and without
hexachloro platinum (IV) acid hexahydrate dissolved in CH3-CH2-OH. In the present study, because such
morphological differences were not the main focus, we performed experiments using such films.
(a)
(b)
100 nm
100 nm
(d)
(c)
100 nm
100 nm
Fig. S1 SEM images of WO3 (a, b) and Pt/WO3 (c, d). Surface images (a, c) and cross-sectional images (b, d).
2
S. 2
Back reaction of Pt/WO3 and WO3 in the presence and absence of O2 (Fig. S2).
The back reaction behaviors of Pt/WO3 and WO3 after the GC and PC reactions are shown in Fig. S2 for samples
stored in the dark under air or N2. It can be clearly seen that the back reaction did not proceed in the absence of O2
for both Pt/WO3 and WO3, whereas it proceeded in the presence of O2.
Air
-40
-20
N2
0
2.0
1.6 (a) WO3
1.2
N2
0.8
Air
0.4
0
0
40
80 120
Time / min.
S / V K-1
-60 (b) WO3
-1000
-800 (d) Pt/WO3
Air
-600
-400
-200
N2
0
50
40
N2
30
20
10 (c) Pt/WO3
Air
0
160
0
40
80 120 160
Time / min.
 / S cm-1
 / S cm-1
S / V K-1
-80
Fig. S2 Back reaction behaviors ( and S) of WO3 (a, b) and Pt/WO3 (c, d) stored in the dark under air or N2.
3
S. 3
Power factor, PF (Fig. S3).
We calculated the power factor (PF), as expressed by S2 for the data in Figs. 5a, 5b and in Fig. 6c as shown in
Fig. S3c and Fig. S3e, respectively. Note that Figs. S3a and S3b are the same as Figs. 5a and 5b, respectively and that
Figs. S3d is the same as Fig. 6c. In Fig. S3c, the reversibility of PF value is not good, whereas that of  and S seemed
to be good. The poor reversibility of PF was in the attributable to the low  region (during back reaction), and the 
values in the region slightly increased with increasing alternating chromic and back reaction cycles.
In contrast, the reversibility of the PF was confirmed to be high, being reflected by good reversible property of 
3.0
PF photo
(e)
2.0
1.0
PF
0
-50
-40
-30
(d)
Sphoto
S
-20
2.4
photo

-10
-1
3.0
1.8
, photo / S cm
S, Sphoto / V K-1 PF×10-3 / W m-1 K-2
and S.
1.2
off off off off off off
on on on on on
FIG. S3 Reversible changes in the electrical conductivity (a), Seebeck coefficient (b), and power factor (c) of Pt/WO3
as a function of time during alternating chromic (white regions) and back (shaded regions) reactions. Plots represent
, S, and PF during simultaneous GC and PC reactions induced by irradiation with UV light (300−400 nm) under a
N2 flow with HCOOH and the back reaction induced by irradiation with visible light (> 500 nm) under atmospheric
conditions. Note that Figs. S3a and S3b are the same as Figs. 5a and 5b, respectively.
Detection of photoconductivity (photo) and photo-Seebeck effect (Sphoto) (d) and power factor (PFphoto) (e) by on-andoff alternation of visible-light irradiation (>500 nm) under N2 flow with HCHO of Pt/WO3 that had previously
undergone UV light irradiation (300−400 nm, N2 with HCHO atmosphere). Pt/WO3. Note that Figs. S3d is the same
as Fig. 6c.
4
S. 4
Schematic diagram of Pt/WO3 (Fig. S4)
The band edge positions of WO3 and Pt are described in Fig. S4a. Those of WO3 and Pt were determined in
previous papers.a,b The band alignments of WO3 and Pt after connecting with each other are shown in Fig. S4b. A
Schottky barrier is formed at the interface between Pt and the CB of WO3, however we can consider that electrons in
the CB of WO3 potentially (or energetically) favor transfer to Pt. Electrons in Pt can also potentially transfer to W5+
state.
(a)
(b)
FIG. S4 Band edge positions of WO3 and Pt (a) and band alignments of WO3 and Pt after connecting with each other
(b). The charge transfer processes are also shown in (b). Note that the uncertainty in the band edge positions amounts
to a few tenths of an eV.
a) A. Ohta, H. Murakami, S. Higashi, S. Miyazaki, J. Phys. Conference Series 417, 012012 (2013).
b) K. Hashimoto, T. Kawai, T. Sakata, J. Phys. Chem. 88, 4083 (1984).
5