Abstract:In this study, Bi2S3 sensitive layer has been grown on the surface of WO3 nanoplate arrays via an in situ approach. The characterization of samples were carried out using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and ultraviolet–visible absorption spectroscopy (UV-vis). The results show that the Bi2S3 layer is uniformly formed on the surface of WO3 nanoplates and less interfacial defects were observed in the interface between the Bi2S3 and WO3. More imp… Show more
“…τD of the ALD and sputtered WO3 films are τD (ALD) = 1.6×10 -2 ms and τD (sputtering) = 3.2×10 -2 ms, respectively. These τD values are lower than that those reported in the literatures, which are around 1 -20 ms 23,58 , which were measured with similar methods and same light sources. The main reason for this difference might be related to the single and much thinner WO3 layer of 50 nm in this work compared to the literature (1 -2 μm).…”
We evaluate the impact of defects in WO3 thin films on the photoelectrochemical (PEC) properties during water splitting. We study physical defects, such as micro holes or cracks, by two different deposition techniques: sputtering and atomic layer deposition (ALD). Chemical defects, such as oxygen vacancies, are tailored by different annealing atmospheres, i.e. air, N2, and O2. The results show that the physical defects inside the film increase the resistance for the charge transfer and also result in a higher recombination rate which inhibits the photocurrent generation. Chemical defects yield in an increased adsorption of OH groups on the film surface and enhance the PEC efficiency. Excess amount of chemical defects can also inhibit the electron transfer, thus decreasing the photocurrent generation. In this study, the highest performance was obtained for WO3 films deposited by ALD and annealed in air, which have the least physical defects and an appropriate amount of oxygen vacancies.
“…τD of the ALD and sputtered WO3 films are τD (ALD) = 1.6×10 -2 ms and τD (sputtering) = 3.2×10 -2 ms, respectively. These τD values are lower than that those reported in the literatures, which are around 1 -20 ms 23,58 , which were measured with similar methods and same light sources. The main reason for this difference might be related to the single and much thinner WO3 layer of 50 nm in this work compared to the literature (1 -2 μm).…”
We evaluate the impact of defects in WO3 thin films on the photoelectrochemical (PEC) properties during water splitting. We study physical defects, such as micro holes or cracks, by two different deposition techniques: sputtering and atomic layer deposition (ALD). Chemical defects, such as oxygen vacancies, are tailored by different annealing atmospheres, i.e. air, N2, and O2. The results show that the physical defects inside the film increase the resistance for the charge transfer and also result in a higher recombination rate which inhibits the photocurrent generation. Chemical defects yield in an increased adsorption of OH groups on the film surface and enhance the PEC efficiency. Excess amount of chemical defects can also inhibit the electron transfer, thus decreasing the photocurrent generation. In this study, the highest performance was obtained for WO3 films deposited by ALD and annealed in air, which have the least physical defects and an appropriate amount of oxygen vacancies.
“…Among those, photoelectrochemical (PEC) water splitting under solar light irradiation has shown their potential by the successful integration of abundant energy source and high efficient catalysts. In order to realize high efficiency PEC systems in view of water splitting, a number of photocatalysts have been investigated including the widespread TiO 2 1 2 3 , ZnO 4 5 6 7 , WO 3 8 9 10 11 , Fe 2 O 3 12 , as well as more innovative catalysts such as Cu 2 O 13 14 15 , and BiVO 4 16 .…”
Layered double hydroxides (LDHs) are bimetallic hydroxides that currently attract considerable attention as co-catalysts in photoelectrochemical (PEC) systems in view of water splitting under solar light. A wide spectrum of LDHs can be easily prepared on demand by tuning their chemical composition and structural morphology. We describe here the electrochemical growth of NiFe-LDH overlayers on Cu2O electrodes and study their PEC behavior. By using the modified Cu2O/NiFe-LDH electrodes we observe a remarkable seven-fold increase of the photocurrent intensity under an applied voltage as low as −0.2 V vs Ag/AgCl. The origin of such a pronounced effect is the improved electron transfer towards the electrolyte brought by the NiFe-LDH overlayer due to an appropriate energy level alignment. Long-term photostability tests reveal that Cu2O/NiFe-LDH photocathodes show no photocurrent loss after 40 hours of operation under light at −0.2 V vs Ag/AgCl low bias condition. These improved performances make Cu2O/NiFe-LDH a suitable photocathode material for low voltage H2 production. Indeed, after 8 hours of H2 production under −0.2 V vs Ag/AgCl the PEC cell delivers a 78% faradaic efficiency. This unprecedented use of Cu2O/NiFe-LDH as an efficient photocathode opens new perspectives in view of low biasd or self-biased PEC water splitting under sunlight illumination.
“…Optical bandgap of CoFe 2 O 4 nanostructure film has been determined using CoFe 2 O 4 nanostructure film coated onto a quartz substrate. Figure 3a show the optical bandgap of CoFe 2 O 4 nanostructure film under different magnetic field strengths determined by using the Tauc relation 31–33 ;where, A is a constant, α is the absorption coefficient, hv is the absorbed photon energy and E g is the optical bandgap.Figure 3( a ) Optical bandgap results of CoFe 2 O 4 nanostructure film under different magnetic field strengths, ( b ) variation of bandgap with magnetic field, ( c ) Raman spectroscopy results of CoFe 2 O 4 film under different magnetic field strengths, ( d ) variation of intensity ratio (I v ) with magnetic field.…”
Efficient solar to hydrogen conversion using photoelectrochemical (PEC) process requires semiconducting photoelectrodes with advanced functionalities, while exhibiting high optical absorption and charge transport properties. Herein, we demonstrate magneto-tunable photocurrent in CoFe2O4 nanostructure film under low applied magnetic fields for efficient PEC properties. Photocurrent is enhanced from ~1.55 mA/cm2 to ~3.47 mA/cm2 upon the application of external magnetic field of 600 Oe leading to ~123% enhancement. This enhancement in the photocurrent is attributed to the reduction of optical bandgap and increase in the depletion width at CoFe2O4/electrolyte interface resulting in an enhanced generation and separation of the photoexcited charge carriers. The reduction of optical bandgap in the presence of magnetic field is correlated to the shifting of Co2+ ions from octahedral to tetrahedral sites which is supported by the Raman spectroscopy results. Electrochemical impedance spectroscopy results confirm a decrease in the charge transfer resistance at the CoFe2O4/electrolyte interface in the presence of magnetic field. This work evidences a coupling of photoexcitation properties with magnetic properties of a ferromagnetic-semiconductor and the effect can be termed as magnetophototronic effect.
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