Solar Hydrogen Generation: Photocatalytic and Photoelectrochemical Methods - Hydrogen Generation, Storage, and Utilization - page 41

(a) (b)

(c) (d)

FIGURE 3.7 (a) Linear sweep voltammograms collected on pristine TiO 2 nanowire and hydrogen-
treated TiO 2 (H:TiO 2 ) nanowires annealed at temperature of 350, 400, and 450°C. (b) IPCE spectra of
pristine TiO 2 and H:TiO 2 nanowires. The inset is the magnified IPCE spectra that highlighted in the dashed
box. (c) Simulated solar-to-hydrogen efficiencies for the pristine TiO 2 and H : TiO 2 samples as a function
of wavelength, by integrating their IPCE spectra collected at −0.6 V versus Ag/AgCl with a standard
AM 1.5G solar spectrum. (d) Mott-Schottky plots collected at a frequency of 5 kHz in the dark for pristine
TiO 2 and H:TiO 2 nanowire. Source : Reproduced with permission from Wang et al. [11]. (See color insert.)

hydrogen treatment at elevated temperatures. Oxygen vacancies serve as
shallow donors that can improve the electrical conductivity of metal oxides
[11, 25]. Notably, hydrogen-treated samples showed substantially increased
photocurrent density, compared with pristine TiO 2 (Fig. 3.7a). A maximum
photocurrent density of around 2.5 mA cm −2 was obtained for the hydrogen-
treated TiO 2 at 0 V versus Ag/AgCl in 1.0 M NaOH aqueous solution [11].
Incident photon-to-current efficiency (IPCE) analysis suggested that the
enhanced photocurrent was due to improved photoactivity of TiO 2 in the UV
region (Fig. 3.7b). The increased IPCE values were attributed to enhanced
charge collection efficiency as expected for hydrogen-treated TiO 2 that has
improved electrical conductivity. By integrating the IPCE spectra with stan-
dard AM 1.5G spectrum, a simulated maximum solar to hydrogen conversion
efficiency of 1.1% was obtained for hydrogen-treated TiO 2 (Fig. 3.7c).