12 Plasmon-Induced Carrier Transfer for Infrared Light Energy …
219
under IR irradiation. Consequently, we conclude that the photo-induced carrier
transfer from the r-Cu 7 S 4 phase to the w-CdS phase in a CdS/Cu 7 S 4 HNC is the
key step contributing to the HER activity.
Remarkably, the CdS/Cu 7 S 4 HNCs showed no notable changes in their catalytic
activity after 36 h, indicating high stability of the CdS/Cu 7 S 4 HNCs. We found that the
amount of evolved H 2 increased with illumination time after a substantial induction
period (Fig. 12.8) [22]. We attribute the induction period of the HER under IR-light
irradiation to in situ deposition of Pt-cocatalyst, which increased the photocatalytic
activity over time. When the Pt-cocatalyst was photodeposited on the CdS/Cu 7 S 4
HNCs beforehand, the time-dependent photocatalytic HER showed no induction
period.
The apparent quantum yield (AQY) was measured under the above photocatalytic
reaction conditions with the use of various monochromic wavelength bandpass filters.
The light intensity was measured with a power meter. The AQY was calculated
according to the following equation:
AQY =
number of reacted electrons
number of incident photons
× 100%
=
number of evolved H 2 molecules × 2
number of incident photons
× 100%
For wavelength-dependent AQY measurements of the photocatalytic HER, we
analyzed the photoreacted gas in a quartz cell (10 mm) with a gas chromatograph (GC2004, Shimadzu, with argon as a carrier gas). A 300-W xenon lamp was irradiated
onto the sample through different wavelength filters for 4 h.
The AQYs obtained at several monochromic light wavelengths were consistent
with the LSPR spectrum of the CdS/Cu 7 S 4 HNCs, indicating that the present photocatalytic reaction was caused by LSPR excitation (Fig. 12.8). The estimated AQY at
1100 nm was 3.8%, which is considerably greater than the previously reported record.
The damping of the AQYs from 1300 to 1500 nm is likely caused by strong absorption
of light by water. Notably, we observed H 2 evolution at 0.023 and 0.022 μmol g
−1 h
−1
from the 1615–2280 and 2093–2547 nm regions (center power density: 6 mW cm
−2 ),
respectively. The Cu 7 S 4 NCs showed no catalytic activity even under visible light
irradiation.
12.5 Mechanism of IR-Induced Photocatalytic H 2
Evolution
Finally, on the basis of the TA measurements, we summarize the mechanism of
IR-induced photocatalytic HER in Fig. 12.9. First, excitation of the Cu 7 S 4 LSPR
band in CdS/Cu 7 S 4 HNCs generated hot carriers in the Cu 7 S 4 phase. Hot electrons
generated in the Cu 7 S 4 phases were then injected into the CdS phases through the
219
under IR irradiation. Consequently, we conclude that the photo-induced carrier
transfer from the r-Cu 7 S 4 phase to the w-CdS phase in a CdS/Cu 7 S 4 HNC is the
key step contributing to the HER activity.
Remarkably, the CdS/Cu 7 S 4 HNCs showed no notable changes in their catalytic
activity after 36 h, indicating high stability of the CdS/Cu 7 S 4 HNCs. We found that the
amount of evolved H 2 increased with illumination time after a substantial induction
period (Fig. 12.8) [22]. We attribute the induction period of the HER under IR-light
irradiation to in situ deposition of Pt-cocatalyst, which increased the photocatalytic
activity over time. When the Pt-cocatalyst was photodeposited on the CdS/Cu 7 S 4
HNCs beforehand, the time-dependent photocatalytic HER showed no induction
period.
The apparent quantum yield (AQY) was measured under the above photocatalytic
reaction conditions with the use of various monochromic wavelength bandpass filters.
The light intensity was measured with a power meter. The AQY was calculated
according to the following equation:
AQY =
number of reacted electrons
number of incident photons
× 100%
=
number of evolved H 2 molecules × 2
number of incident photons
× 100%
For wavelength-dependent AQY measurements of the photocatalytic HER, we
analyzed the photoreacted gas in a quartz cell (10 mm) with a gas chromatograph (GC2004, Shimadzu, with argon as a carrier gas). A 300-W xenon lamp was irradiated
onto the sample through different wavelength filters for 4 h.
The AQYs obtained at several monochromic light wavelengths were consistent
with the LSPR spectrum of the CdS/Cu 7 S 4 HNCs, indicating that the present photocatalytic reaction was caused by LSPR excitation (Fig. 12.8). The estimated AQY at
1100 nm was 3.8%, which is considerably greater than the previously reported record.
The damping of the AQYs from 1300 to 1500 nm is likely caused by strong absorption
of light by water. Notably, we observed H 2 evolution at 0.023 and 0.022 μmol g
−1 h
−1
from the 1615–2280 and 2093–2547 nm regions (center power density: 6 mW cm
−2 ),
respectively. The Cu 7 S 4 NCs showed no catalytic activity even under visible light
irradiation.
12.5 Mechanism of IR-Induced Photocatalytic H 2
Evolution
Finally, on the basis of the TA measurements, we summarize the mechanism of
IR-induced photocatalytic HER in Fig. 12.9. First, excitation of the Cu 7 S 4 LSPR
band in CdS/Cu 7 S 4 HNCs generated hot carriers in the Cu 7 S 4 phase. Hot electrons
generated in the Cu 7 S 4 phases were then injected into the CdS phases through the