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1.
Photo-assisted H2 evolution has been realized over the new heterosystem CuFeO2/SnO2 without any noble metal and was studied in connection with some physical parameters. The delafossite CuFeO2 has been prepared by thermal decomposition from various salts. The polarity of generated voltage is positive indicating that the materials exhibit p-type conductivity whereas the electroneutrality is achieved by oxygen insertion. The plot of the logarithm (conductivity) vs. T−1 gives average activation energy of 0.12 eV. CuFeO2 is a narrow band gap semiconductor with an optical gap of 1.32 eV. The oxide was characterized photoelectrochemically; its conduction band (−1.09 VRHE) is located below that of SnO2 (−0.86 VRHE) at pH ∼13.5 itself more negative than the H2O/H2 level leading to a thermodynamically favorable H2 evolution under visible irradiation. The sensitizer CuFeO2, working as an electron pump, is stable towards photocorrosion by hole consumption reactions involving the reducing agents X2− (=S2O32− and SO32−). The photoactivity was dependent on the precursor and the best performance (0.026 ml h−1 mg−1) was obtained in S2O32− (pH ∼13.5) over CuFeO2 synthesized from nitrate with a mass ratio (CuFeO2/SnO2) equal to unity. A quantum yield of 0.5% was obtained under polychromatic light. H2 liberation occurs concomitantly with the oxidation of S2O32− to dithionate and sulfate. The tendency towards saturation, in a closed system, is mainly ascribed to the competitive reduction of the end product S2O62−. 相似文献
2.
Prasad Manjusri Sirimanne Kazunori Takahashi Noriyuki Sonoyama Tadayoshi Sakata 《Solar Energy Materials & Solar Cells》2002,73(2)
Sintered Bi2O3 pellets exhibited insulating properties at room temperature. Partial reduction of sintered Bi2O3 pellets increased the conductivity. Reduced Bi2O3 pellets exhibited n-type semiconductor properties. Microcrystals of Bi2S3 were formed on sintered Bi2O3 pellets by sulfurizing them in H2S atmosphere. The direct band-gap and indirect band-gap of Bi2S3 were evaluated as 1.2 and 0.4 eV, respectively. A high incident photon to current conversion efficiency in the near IR region was observed on Bi2S3|Bi2O3 electrodes. Photocurrent generation of Bi2S3|Bi2O3 electrodes was explained from the viewpoint of semiconductor sensitization. The flat band potential of Bi2S3 was evaluated as −1.1 V vs. Ag|AgCl in aqueous polysulfide redox electrolyte (1 M OH−, 1 M S2−, 10−2 M S). 相似文献
3.
Prasad Manjusri Sirimanne Satoshi Shiozaki Noriyuki Sonoyama Tadayoshi Sakata 《Solar Energy Materials & Solar Cells》2000,62(3)
Microcrystals of In2S3 were formed on sintered In2O3 pellets by sulfurizing in H2S atmosphere. The flat band potential of compound In2S3|In2O3 electrodes was evaluated as −1.0 V vs Ag|AgCl in 1 M KOH, 1 M Na2S, 10−2 M S. Significantly enhanced photocurrent was observed on compound In2S3|In2O3 electrodes with a lower degree of sulfurization to that of compound In2S3|In2O3 electrodes with higher degree of sulfurization. Photocurrent generation of compound In2S3|In2O3 electrodes was explained from the viewpoint of semiconductor sensitization. 相似文献
4.
This is a report on the production of O2 and H2 from photocatalytic and photochemical processes in the WO3–H2O–Ce4+aq–hν system. The photoproduction of O2 and H2 was studied over the range of WO3 concentrations from 2 to 8 g dm−3, and conduction band electron scavenger concentrations 1–20 mM Ceaq4+. Medium and high concentrations of the electron scavenger gave mainly O2 as the main product. Dilute solutions of [Ceaq4+]< 2 mM initially produced dioxygen, and then hydrogen after an induction period of 3–4 h. Yields of 140–250 μmol O2 h−1 and 1–7 μmol H2 h−1 were obtained and were found to depend on the physical properties and content of WO3, the concentration of the electron scavenger, illumination period and wavelength, and the radiation geometry. The photoactivity of the suspension was correlated to the level of crystallinity of WO3 powders. The studied system utilizes WO3 to accomplish the initial light absorption, charge separation, and production of O2 and H+ from the interaction of water molecules with photogenerated WO3 valence band holes, in the presence of Ce4+aq species as a scavenger of conduction band electrons. This is followed by the evolution of H2 from a homogeneous photochemical reduction of H+ and/or H2O by photoexcited Ce3+aq, formed from the earlier reduction of Ce4+aq. The obtained results show that, with an appropriate design, tungsten trioxide is a promising material that can be used as a photoactive component in energy conversion systems or in environmental photocatalysis, using artificial or solar light. 相似文献
5.
A possibility of semiconductor-sensitized thin film solar cells have been proposed. Nanocrystalline In2S3-modified In2O3 electrodes were prepared with sulfidation of In2O3 thin film electrodes under H2S atmosphere. The band gap (Eg) of In2S3 estimated from the onset of the absorption spectrum was approximately 2.0 eV. The photovoltaic properties of a photoelectrochemical solar cell based on In2S3/In2O3 thin film electrodes and I−/I3− redox electrolytes were investigated. This photoelectrochemical cell could convert visible light of 400–700 nm to electron. A highly efficient incident photon-to-electron conversion efficiency (IPCE) of 33% was obtained at 410 nm. The solar energy conversion efficiency, η, under AM 1.5 (100 mW cm−2) was 0.31% with a short-circuit photocurrent density (Jsc) of 3.10 mA cm−2, a open-circuit photovoltage (Voc) of 0.26 V, and a fill factor ( ff ) of 0.38. 相似文献
6.
The hydrogen photo-evolution was successfully achieved in aqueous (Fe1−xCrx)2O3 suspensions (0 ≤ x ≤ 1). The solid solution has been prepared by incipient wetness impregnation and characterized by X-ray diffraction, BET, transport properties and photo-electrochemistry. The oxides crystallize in the corundum structure, they exhibit n-type conductivity with activation energy of ∼0.1 eV and the conduction occurs via adiabatic polaron hops. The characterization of the band edges has been studied by the Mott Schottky plots. The onset potential of the photo-current is ∼0.2 V cathodic with respect to the flat band potential, implying a small existence of surface states within the gap region. The absorption of visible light promotes electrons into (Fe1−xCrx)2O3-CB with a potential (∼−0.5 VSCE) sufficient to reduce water into hydrogen. As expected, the quantum yield increases with decreasing the electro affinity through the substitution of iron by the more electropositive chromium which increases the band bending at the interface and favours the charge separation. The generated photo-voltage was sufficient to promote simultaneously H2O reduction and SO32− oxidation in the energetically downhill reaction (H2O + SO32− → H2 + SO42−, ΔG = −17.68 kJ mol−1). The best activity occurs over Fe1.2Cr0.8O3 in SO32− (0.1 M) solution with H2 liberation rate of 21.7 μmol g−1 min−1 and a quantum yield 0.06% under polychromatic light. Over time, a pronounced deceleration occurs, due to the competitive reduction of the end product S2O62−. 相似文献
7.
L. Djellal A. Bouguelia M. Kadi Hanifi M. Trari 《Solar Energy Materials & Solar Cells》2008,92(5):594-600
Dense CuInSe2 of high quality, prepared by the fusion technique in evacuated quartz ampoule from stoichiometric melt, crystallizes in the chalcopyrite structure. Compositional analysis carried out by secondary ion mass spectrometry (SIMS) and energy dispersive spectroscopy (EDS) indicates a uniform distribution of elements through the depth and a composition close to the stoichiometry. The diffuse reflectance spectrum gives a band gap at 0.94 eV. The electrical conductivity follows an Arrhenius-type law with activation energy of 23 meV in conformity with polarons hopping. Above 320 °C, CuInSe2 undergoes an irreversible oxidation. The thermal variation of the thermopower indicates p-type behavior attributed to copper deficiency and a hole mobility μ300 K of 0.133 cm2 V−1 s−1, thermally activated. In KCl media, the compound exhibits an excellent chemical stability with a corrosion rate of 8 μmol cm−2 month−1. The photo-electrochemical properties, investigated for the first time on the ingots, confirm the p-type conductivity. From the capacitance measurements, the flat band potential (Vfb=−0.62VSCE) and the holes density (NA=4×1017 cm−3) were determined. The valence band, located at 4.43 eV below vacuum, is made up of mainly Se orbital with little admixture of Cu character. The change of the electrolyte causes a variation in the potential Vfb (dVfb/dpH=−0.058 V pH−1) indicating strong OH− adsorption. The fill factor in S2− media was found to be 0.54; such result was corroborated by semi-logarithmic plots. 相似文献
8.
A. Yamamoto M. Nakamura A. Seki E. L. Li A. Hashimoto S. Nakamura 《Solar Energy Materials & Solar Cells》2003,75(3-4):451-456
A simple spray method for the preparation of pyrite (FeS2) thin films has been studied using FeSO4 and (NH4)2Sx as precursors for Fe and S, respectively. Aqueous solutions of these precursors are sprayed alternately onto a substrate heated up to 120°C. Although Fe–S compounds including pyrite are formed on the substrate by the spraying, sulfurization of deposited films is needed to convert other phases such as FeS or marcasite into pyrite. A single-phase pyrite film is obtained after the sulfurization in a H2S atmosphere at around 500°C for 30 min. All pyrite films prepared show p-type conduction. They have a carrier concentration (p) in the range 1016–1020 cm−3 and a Hall mobility (μH) in the range 200–1 cm2/V s. The best electrical properties (p=7×1016 cm−3, μH=210 cm2/V s) for a pyrite film prepared here show the excellence of this method. The use of a lower concentration FeSO4 solution is found to enhance grain growth of pyrite crystals and also to improve electrical properties of pyrite films. 相似文献
9.
Films of polycrystalline Bi2S3 have been prepared onto bismuth and platinum substrates by electrodeposition from an aqueous sulfide bath. The films were thin, uniform and well adhered. Bi2S3 is a direct band gap semiconductor with a value of 1.28 eV optimally matched with the solar spectrum. The photoelectrochemical study was undertaken for the generation of hydrogen by using illuminated n-Bi2S3 particles; it was found that hydrogen evolution depends highly on the synthesis method of powder. Impregnation of platinum onto Bi2S3 shows a production enhancement of about 25%. The most active photocatalyst, prepared by a solvent thermal process and loaded with Pt in 0.1 M S2− alkaline electrolyte, yields 2.13×10−2 ml mg−1 of H2 after 4 h of irradiation with the visible output of a 500 W halogen lamp. 相似文献
10.
The physical properties and photoelectrochemical characterization of the spinel ZnFe2O4, elaborated by chemical route, have been investigated for the hydrogen production under visible light. The forbidden band is found to be 1.92 eV and the transition is indirectly allowed. The electrical conduction occurs by small polaron hopping with activation energy of 0.20 eV. p-type conductivity is evidenced from positive thermopower and cathodic photocurrent. The flat band potential (0.18 VSCE) determined from the capacitance measurements is suitably positioned with respect to H2O/H2 level (−0.85 VSCE). Hence, ZnFe2O4 is found to be an efficient photocatalyst for hydrogen generation under visible light. The photoactivity increases significantly when the spinel is combined with a wide band gap semiconductor. The best performance with a hydrogen rate evolution of 9.2 cm3 h−1 (mg catalyst)−1 occurs over the new hetero-system ZnFe2O4/SrTiO3 in Na2S2O3 (0.025 M) solution. 相似文献
11.
Xingbao Zhu Zhe Lü Bo Wei Kongfa Chen Mingliang Liu Xiqiang Huang Wenhui Su 《Journal of power sources》2009,190(2):326-330
The optimization of electrodes for solid oxide fuel cells (SOFCs) has been achieved via a wet impregnation method. Pure La0.75Sr0.25Cr0.5Mn0.5O3−δ (LSCrM) anodes are modified using Ni(NO3)2 and/or Ce(NO3)3/(Sm,Ce)(NO3)x solution. Several yttria-stabilized zirconia (YSZ) electrolyte-supported fuel cells are tested to clarify the contribution of Ni and/or CeO2 to the cell performance. For the cell using pure-LSCrM anodes, the maximum power density (Pmax) at 850 °C is 198 mW cm−2 when dry H2 and air are used as the fuel and oxidant, respectively. When H2 is changed to CH4, the value of Pmax is 32 mW cm−2. After 8.9 wt.% Ni and 5.8 wt.% CeO2 are introduced into the LSCrM anode, the cell exhibits increased values of Pmax 432, 681, 948 and 1135 mW cm−2 at 700, 750, 800 and 850 °C, respectively, with dry H2 as fuel and air as oxidant. When O2 at 50 mL min−1 is used as the oxidant, the value of Pmax increases to 1450 mW cm−2 at 850 °C. When dry CH4 is used as fuel and air as oxidant, the values of Pmax reach 95, 197, 421 and 645 mW cm−2 at 750, 800, 850 and 900 °C, respectively. The introduction of Ni greatly improves the performance of the LSCrM anode but does not cause any carbon deposit. 相似文献
12.
Synthesis and characterization of oxygen-rich delafossite CuYO2+x—Application to H2-photo production
M. Younsi S. Saadi A. Bouguelia A. Aider M. Trari 《Solar Energy Materials & Solar Cells》2007,91(12):1102-1109
Here we report the synthesis and photo electrochemical properties of super oxides CuYO2.50 and CuYO2.25 prepared from the delafossite CuYO2, respectively, by thermal oxidation at 380 °C under O2-flow and soft chemistry in NaBrO solution (5 N). Their applications as catalysts for H2 evolution upon visible light were investigated. The oxygen insertion was accompanied by partial oxidation of Cu+. For CuYO2.25, the chemical analyses revealed the presence of mixed valent states containing at least formally an equal number of Cu+ and Cu2+. The thermal analysis (TGA) under reducing atmosphere indicates that oxygen is inserted in different crystallographic sites, for CuYO2.25 it exhibits a two-step reduction mechanism with restoration of the parent oxide. In air, CuYO2+x is thermally stable up to 500 °C above which it undergoes irreversible conversion into Cu2Y2O5. They display p-type behavior ascribed to oxygen insertion and the conduction occurs by hopping mechanism between mixed copper valences. Under illumination, the oxides are stabilized by hole consumption reactions involving SO32− and S2− as holes scavengers. The flat-band potentials, lying between 0.17 and 0.26 VSCE, allow a spontaneous H2-photo formation. The rate of H2-evolution is altered by the oxygen insertion and the best photo activity (1.33 μmol h−1 mg−1) was obtained over CuYO2.25 immersed in S2− solution (0.025 M); CuYO2 is also reported for a comparison goal. Over time, the photoactivity is slowed down because of the competitive reduction of H2O with the final products namely S2O62− and Sn2−. 相似文献
13.
Photocatalytic hydrogen evolution over CuCrO2 总被引:1,自引:0,他引:1
We have been studying the technical feasibility of a photochemical H2 evolution based on a dispersion of CuCrO2 powder in aqueous electrolytes containing various reducing agents (S2−, and ). The title oxide combines a fair resistance to corrosion with an optimal band gap Eg of 1.32 eV. The intercalation of a small amount of oxygen should be accompanied by a partial oxidation of Cu+ into Cu2+ implying a p-type semiconductivity. The S2− oxidation inhibits the photocorrosion and the H2 evolution increases parallel to polysulfides formation. Most of H2 is produced when p-CuCrO2 is connected to n-Cu2O formed in situ. H2 liberation proceeds mostly on CuCrO2 while the oxidation of S2− takes place over Cu2O surface and the hetero system Cu2O/CuCrO2 is optimized with respect to some physical parameters. The photoactivity is dependent on preparation conditions and lowering the synthesis temperature through nitrate route leads to an increase in specific surface area Ssp. The photoelectrochemical H2 production is a multistep process where the rate determining step is the arrival of electrons at the interface because of their low mobility. Prolonged irradiation (>80 min) leads to a pronounced decrease of the photoactivity; the tendency toward saturation is due to the undesired back reduction of polysulfides in a closed system and to their strong absorption in the visible region (λmax = 520 nm). 相似文献
14.
The n-CdZn(S1−xSex) and p-CuIn(S1−xSex)2 thin films have been grown by the solution growth technique (SGT) on glass substrates. Also the heterojunction (p–n) based on n-CdZn (S1−xSex)2 and p-CuIn (S1−xSex)2 thin films fabricated by same technique. The n-CdZn(S1−xSex)2 thin film has been used as a window material which reduced the lattice mismatch problem at the junction with CuIn (S1−xSex)2 thin film as an absorber layer for stable solar cell preparation. Elemental analysis of the n-CdZn (S1−xSex)2 and p-CuIn(S1−xSex)2 thin films was confirmed by energy-dispersive analysis of X-ray (EDAX). The structural and optical properties were changed with respect to composition ‘x’ values. The best results of these parameters were obtained at x=0.5 composition. The uniform morphology of each film as well as the continuous smooth thickness deposition onto the glass substrates was confirmed by SEM study. The optical band gaps were determined from transmittance spectra in the range of 350–1000 nm. These values are 1.22 and 2.39 eV for CuIn(S0.5Se0.5)2 and CdZn(S0.5Se0.5)2 thin films, respectively. J–V characteristic was measured for the n-CdZn(S1−xSex)2/p-CuIn(S1−xSex)2 heterojunction thin films under light illumination. The device parameters Voc=474.4 mV, Jsc=13.21 mA/cm2, FF=47.8% and η=3.5% under an illumination of 85 mW/cm2 on a cell active area of 1 cm2 have been calculated for solar cell fabrication. The J–V characteristic of the device under dark condition was also studied and the ideality factor was calculated which is equal to 1.9 for n-CdZn(S0.5Se0.5)2/p-CuIn(S0.5Se0.5)2 heterojunction thin films. 相似文献
15.
P. Guha D. Das A. B. Maity D. Ganguli S. Chaudhuri 《Solar Energy Materials & Solar Cells》2003,80(1):115-130
CuInS2 powder was prepared by wet chemical route. The chalcopyrite structure of the powder was revealed by XRD studies. Raman measurements of the powder sample indicated four prominent peaks at 292, 305, 340 and 472 cm−1. The possible origin of the 305 cm−1 peak was investigated and was found to be some local vibration in the structure. The peaks at 292 and 340 cm−1 were ascribed to A1 and B2 modes, respectively. The peak at 472 cm−1 which was due to the formation of SO4−2 ion at lower pH value of the precursor solution could be eliminated by using pH>11.0. Photoluminescence (PL) studies of the CuInS2 powder indicated two distinct peaks at 1.49 and 1.42 eV. Post deposition annealing treatment in H2 atmosphere revealed the formation of excess sulphur vacancy leading to the peak at 1.42 eV in the PL spectra while O2 annealing of the powder created a deep defect level at 1.10 eV. Thick CuInS2 films were prepared by Doctor's blade technique. Optical transmittance studies of these films indicated direct allowed transition at 1.5 eV. 相似文献
16.
The present work deals with the photoelectrochemical hydrogen production over the spinel ZnCr2O4. The photoactivity is dependent on the synthesis conditions and the oxide has been prepared by nitrate way in order to produce homogeneous powder with large active surface. The transport properties indicate p-type conductivity with activation energy of 0.21 eV. A corrosion potential of 0.404 VSCE and an exchange current density of 50 μA cm−2 have been determined from the semi logarithm plot. The photocurrent onset potential, assimilated to the flat band potential, was found to be −0.39 VSCE. ZnCr2O4/S2O32− is a self driven system where absorption of light promotes electrons into the conduction band with a potential (−1 V) sufficient to reduce water into hydrogen. The activity shows a tendency toward saturation whose deceleration is the result of the competitive reductions of end products namely S2O62− and S2O42− with water. A comparative study with CuCr2O4 is reported. 相似文献
17.
An energy efficient conversion of ethane to ethylene involving simultaneous oxidative conversion (which is exothermic) and thermal cracking (which is endothermic) reactions of ethane in the presence of steam (steam/C2H6 mol RATIO=1.0) and limited O2 (C2H6/O2 mol ratio 4.0) over a BaO-promoted La2O3 supported on low surface area macroporous silica-alumina commercial catalyst carrier has been thoroughly investigated. Influence of various process parameters such as temperature (700–850°C), C2H6/O2 feed ratio (4.0–8.0) and space velocity (50,000–200,000 cm3 g−1 h−1) on the conversion, product selectivity and net heat of reactions in the process has also been studied. At all the process conditions, there was no coke deposition on the catalyst. High selectivity ( 85%) for C2+ olefins (at 50–60% conversion) can be obtained in the process at a low contact time (<10 ms), particularly for the higher C2H6/O2 ratios ( 6.0) and temperatures ( 800°C). The process exothermicity is decreased appreciably with increasing the temperature and/ or the C2H6/O2 ratio. The net heat of reaction in the process can be controlled by manipulating the C2H6/O2 ratio and reaction temperature. Also, because of simultaneously occurring endothermic and exothermic reactions, the process is highly energy efficient and non-hazardous. 相似文献
18.
The effect of H2O2 on the Pt dissolution in 0.5 mol dm−3 H2SO4 was investigated using an electrochemical quartz crystal microbalance (EQCM). For the potential cycling at 50 mV s−1, the Pt weight irreversibly decreases in a N2 atmosphere with H2O2, while only a negligible Pt weight-loss is observed in the N2 and O2 atmospheres without H2O2. The EQCM data measured by the potential step showed that the Pt dissolution in the presence of H2O2 depends on the electrode potential and the H2O2 concentration. For the stationary electrolysis, the Pt dissolution occurs at 0.61–1.06 and 1.06–1.36 V vs. RHE. It should be noted that the Pt dissolution phenomenon in the presence of H2O2 is also affected by the potential scanning time. Based on these results, H2O2 is considered not only to contribute to the formation of Pt-oxide causing the cathodic Pt dissolution, but also to participate in the anodic Pt dissolution and the chemical Pt dissolution. 相似文献
19.
The phase diagram of the Na2O–MnO–Fe2O3 system forms the basis for thermodynamic consideration of H2 production in water splitting with the Na2CO3/MnFe2O4/Fe2O3 system. Sodium iron manganese oxides Na0.71(Mn1−x, Fex)O2+δwere observed in the phase diagram at T=1273 K under PO2=1.23×10−5 atm. Confirmation of this phase, especially for x>0.5, suggests the possibility of H2 generation under this oxygen partial pressure and results in a value of 1:37 for the ratio of PH2:PH2O in the H2 generation step of water splitting. This oxygen partial pressure is realized by the decomposition of carbon dioxide (CO2=CO+0.5O2) and it is concluded that the H2 generation step can proceed under CO2 atmosphere. 相似文献
20.
Pt electrode dissolution has been investigated using an electrochemical quartz crystal microbalance (EQCM) in H2O2-containing 0.5 mol dm−3 H2SO4. The Pt electrode weight-loss of ca. 0.4 μg cm−2 is observed during nine potential sweeps between 0.01 and 1.36 V vs. RHE. In contrast, the Pt electrode weight-loss is negligible without H2O2 (<0.05 μg cm−2). To support the EQCM results, the weight-decrease amounts of a Pt disk electrode and amounts of Pt dissolved in the solutions were measured after similar successive potential cycles. As a result, these results agreed well with the EQCM results. Furthermore, the H2O2 concentration dependence of the Pt weight-decrease rate was assessed by successive potential steps. These EQCM data indicated that the increase in H2O2 accelerates the Pt dissolution. Based on these results, H2O2 is known to be a major factor contributing to the Pt dissolution. 相似文献