New water splitting solid solution photocatalysts with the composition of Gd1-xBixVO4 (x = 0, 0.3, 0.5, 0.7, 0.8, 0.9, 0.95,
1.0) were synthesized by a solid-state reaction. Gd0.3Bi0.7VO4 was found as novel photocatalyst with both O2 evolution
from aqueous solution of sacrificial reagent AgNO3 under visible-light irradiation (λ > 420nm) and H2 evolution from
aqueous solution of sacrificial reagent CH3OH under near visible-light irradiation (λ > 380nm). The obtained solid
solutions such as GdVO4, Gd0.7Bi0.3VO4, Gd0.5Bi0.5VO4, and Gd0.3Bi0.7VO4 crystallized in zircon-tetragonal crystal
structures, while Gd0.05Bi0.95VO4 and BiVO4 crystallized in scheelite-monoclinic structures. The diffuse reflectance
spectra of the solid solutions shift monotonically to a long wavelength as the ratio of Bi ions to Gd ions increases in the
solid solution. The structure and water splitting activity were discussed in relation to the solid solution compositions and
photophysical properties. Furthermore, new thin film photoelectrodes of Gd0.7Bi0.3VO4 and BiVO4 for solar hydrogen
production were prepared by metal organic decomposition (MOD) method and polymerized complex (PC) method. The
photoelectrodes were characterized by using Grazing Incidence X-ray Analysis (GIXA), SEM, cyclic voltammetry (CV)
and IPCE measurement. Finally, solar energy conversion efficiency for water splitting (STH efficiency) was measured.
Best STH efficiencies of BiVO4 and Gd0.3Bi0.7VO4 thin film photoelectrodes were 0.05% at the applied potential of 0.9 V
and 0.025% at the applied potential of 0.5 V vs NHE, respectively.
KEYWORDS: Dye sensitized solar cells, Ruthenium, Solar cells, Solar energy, Absorption, Energy efficiency, Quantum efficiency, Dysprosium, Particles, Electrodes
We have synthesized a new series of Ru complexes having β-diketonate and terpyridine ((tctpy = 4,4',4''-
tricarboxy-2,2':6',2''-terpyridine) ligands as efficient panchromatic photosensitizers. Then we fabricated dye-sensitized
solar cells (DSCs) using these Ru dyes. It was observed that newly synthesized Ru dye, Ru(tctpy)(dfac)NCS (3) (dfac =
1,1-difluoroacetylacetone), as well as previously synthesized Ru dyes, Ru(tctpy)(acac)NCS (1)(acac = acetylacetone)
and Ru(tctpy)(tfac)NCS (2) (tfac = 1,1,1,-trifluoroacetylacetone) could absorb light wider than that of Ru(tctpy)(NCS)3
(Black dye), which was well known as one of the best panchromatic dyes. DSC using dye (1) showed a low solar energy
conversion efficiency (η) because of a narrow energy gap (ΔG1) between HOMO level of dye(1) and I-/I3- redox energy
level. On the other hand, DSC using dye (2) produced such a high photocurrent (Jsc) as 25.4mA/cm2. However this cell
could not show a high efficiency such as 10% because of a narrow energy gap (ΔG2) between LOMO level of dye (2)
and TiO2 conduction band. Finally, DSC using newly synthesized dye (3) showed such a high efficiency as 10.2%
because of its suitable HOMO-LUMO energy levels, having optimum energy gaps of ΔG1 and ΔG2.
KEYWORDS: Semiconductors, Oxides, Water splitting, Hydrogen production, Dye sensitized solar cells, Visible radiation, Electrodes, Solar cells, Solar energy, Iron
Photocatalytic and photoelectrochemical approaches to solar hydrogen production in our group were introduced. In
photocatalytic water splitting system using NiOx/ TiO2 powder photocatalyst with concentrated Na2CO3 aqueous solution,
solar energy conversion efficiency to H2 and O2 production (STH efficiency) was 0.016%. In addition, STH efficiency of
visible light responding photocatalyst, NiOx/ promoted In0.9Ni0.1TaO4, was estimated at 0.03%. In photoelectrochemical
system using an oxide semiconductor film phptoelectrode, STH efficiencies of meosporous TiO2 (Anatase) , mesoporous
visible light responding S-doped TiO2 (Anatase) and WO3 film were 0.32-0.44% at applied potential of 0.35 V vs NHE,
0.14% at 0.55 V and 0.44% at 0.9 V, respectively. Finally, solar hydrogen production by tandem cell system composed
of an oxide semiconductor photoelectrode, a Pt wire counter electrode and a dye-sensitized solar cell (DSC) was
investigated. As photoelectrodes, meosporous TiO2 (Anatase), mesoporous S-doped TiO2 (Anatase), WO3, BiVO4 and
Fe2O3 film were tested. STH efficiency of tandem cell system composed of a WO3 film photoelectrode, and a two-series-connected
DSC (Voc = 1.4 V) was 2.5-2.8%. In conclusion, it is speculated that more than 5% STH efficiency will be
obtained by tandem cell system composed of an oxide semiconductor photoelectrode and a two-series-connected DSC in
near future. This suggests a cost-effective and practical application of this system for solar hydrogen production.
KEYWORDS: Visible radiation, Electrodes, Water splitting, Solar energy, Platinum, Lamps, Hydrogen production, Particles, Dye sensitized solar cells, Energy efficiency
Photoelectrochemical water splitting into H2 and O2 was investigated using TiO2 based photoelectrodes. First, influence of photoelectorde structure on water splitting was studied through photocurrent observation. Solar energy conversion efficiency to H2 (STH) of mesoporous TiO2 photoelectode, composed of anatase TiO2 particles of 20nm in diameter, with 10μ thickness on FTO glass was 0.32% under 0.4V vs RHE, producing 0.39mA/cm2. The quantum efficiency of water splitting at 360nm was 27%. Then, visible light absorbing mesoporous N-doped and S-doped anatase TiO2 photoelectrodes were studied. Visible light absorbing properties of these photoelectrodes were dramatically decreased with increasing calcination temperature to 550°C. However, photocurrent such as 1μA/cm2 was observed under 0.94V vs RHE and visible light irradiation using 300W-Xe lamp with 410nm cut off filter. Overall photocurrent of N-doped and S-doped TiO2 photoelectrode was about 1/5 to 1/10 of that of non-doped TiO2 photoelectrodes. Finally, solar hydrogen production by a tandem cell, composed of a mesoporous TiO2 based photoelectrode, a Pt wire electrode and a Black dye-sensitized solar cell, was studied. STH of a non-doped TiO2 photoelectrode system was 0.53% but STH of a S-doped TiO2 photoelectrode system was 0.15%, which was 1/3 lower than that of a non-doped TiO2 photoelectrodes.
Conference Committee Involvement (11)
Solar Hydrogen and Nanotechnology XI
30 August 2016 | San Diego, California, United States
Solar Hydrogen and Nanotechnology X
9 August 2015 | San Diego, California, United States
Solar Hydrogen and Nanotechnology IX
19 August 2014 | San Diego, California, United States
Solar Hydrogen and Nanotechnology VIII
28 August 2013 | San Diego, California, United States
Solar Hydrogen and Nanotechnology VII
13 August 2012 | San Diego, California, United States
Solar Hydrogen and Nanotechnology VI
23 August 2011 | San Diego, California, United States
Solar Hydrogen and Nanotechnology V
3 August 2010 | San Diego, California, United States
Solar Hydrogen and Nanotechnology IV
3 August 2009 | San Diego, California, United States
Solar Hydrogen and Nanotechnology III
11 August 2008 | San Diego, California, United States
Solar Hydrogen and Nanotechnology II
27 August 2007 | San Diego, California, United States
Solar Hydrogen and Nanotechnology
14 August 2006 | San Diego, California, United States
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