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1.
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   

2.
The optical, electrical and photo-electrochemical properties of dense hematite α-Fe2O3 have been studied for the photo-catalytic hydrogen production. The band gap was evaluated at 1.96 eV from the diffuse reflectance spectrum and the transition is directly allowed; further indirect transition occurs at 2.04 eV. The oxygen deficiency permits the altering of the transport properties and the oxide exhibits n type behavior with activation energy of 0.11 eV. α-Fe2O3 is found to be photo-electrochemically active. The flat band potential Vfb (−0.51 VSCE) and the density ND (19.12 × 1019 cm−3) were obtained respectively by extrapolating the linear part to C−2 = 0 and the slope of the Mott–Schottky plot. The complex impedance pattern is circular in the high frequency region followed by a straight line in the low frequency one, a behavior attributed to the Warburg ionic diffusion. The conduction band edge (−0.62 VSCE) lies below the H2O/H2 level (−0.50 VSCE) and Fe2O3 offers the possibility to be used as hydrogen photocathode. The best activity was obtained in SO32− (0.5 M, pH 13.8) solution with a rate evolution of 6 ml (g catalyst)−1 min−1.  相似文献   

3.
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   

4.
A porous spherical aggregation of Li4Mn5O12 nanorods with the particle size of 3 μm is prepared by oxidizing LiMn2O4 powder with (NH4)2S2O8 under hydrothermal conditions. The result displays that concentration of (NH4)2S2O8 plays a key role in forming the porous spherical aggregation and the optimal concentration of oxidant is found to be 1.5 mol L−1. The mechanism for the formation of the porous spherical aggregation is proposed. The electrochemical capacitance performance is tested by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge/discharge. The porous spherical aggregation exhibits a good electrochemical performance. It could deliver 375 F g−1 within potential range 0-1.4 V at a scan rate of 5 mV s−1 in 1 mol L−1 Li2SO4 and the value is cut down to less than 0.024 F g−1 per cycling period in 1000 cycles.  相似文献   

5.
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   

6.
The all-solid-state Li–In/Li4Ti5O12 cell using the 80Li2S·20P2S5 (mol%) solid electrolyte was assembled to investigate rate performances. It was difficult to obtain the stable performance at the charge current density of 3.8 mA cm−2 in the all-solid-state cell. In order to improve the rate performance, the pulverized Li4Ti5O12 particles were applied to the all-solid-state cell, which retained the reversible capacity of about 90 mAh g−1 at 3.8 mA cm−2. The 70Li2S·27P2S5·3P2O5 glass–ceramic, which exhibits the higher lithium ion conductivity than the 80Li2S·20P2S5 solid electrolyte, was also used. The Li–In/70Li2S·27P2S5·3P2O5 glass–ceramic/pulverized Li4Ti5O12 cell was charged at a current density higher than 3.8 mA cm−2 and showed the reversible capacity of about 30 mAh g−1 even at 10 mA cm−2 at room temperature.  相似文献   

7.
Cu0.04V2O5 was prepared by a precipitation method followed by heat treatment at 300 and 600 °C. The material prepared at 300 °C showed porous morphology, whereas that prepared at 600 °C was highly crystalline. X-ray diffraction, Raman scattering and Fourier transform infrared spectroscopy showed both materials exhibiting the same structure as that of V2O5, with a slight lattice expansion. X-ray absorption spectroscopy confirmed the presence of V4+ cations in Cu0.04V2O5, which would increase the electronic conductivity of V2O5. Cu0.04V2O5 showed better electrochemical performance than V2O5 because of its high electronic conductivity and good structural stability. The material prepared at 600 °C delivered a reversible discharge capacity over 160 mAh g−1 after 60 cycles at a C rate of C/5.6. The material prepared at 300 °C showed good high-rate performance, which delivered a reversible capacity ∼100 mAh g−1 when cycled at C/1.9. The discrepancy in the rate performance of Cu0.04V2O5 was attributed to the morphology of materials.  相似文献   

8.
Vanadium oxide films were synthesised by chemical vapour deposition (CVD) from pure of triisopropoxyvanadium oxide (VO(OC3H7)3) and oxygen as precursors. The influence of the substrate on the crystallinity of the vanadium oxide films was studied before and after annealing at 500 °C. On mica substrates, as-deposited film was composed of crystalline V2O5 as revealed by XRD. On Pt, Ti, stainless steel, glass and F-doped SnO2 substrates, an annealing procedure was required to get V2O5. SEM investigations have clearly evidence V2O5 plates but the kinetics growth seems to be strongly dependent on the nature of the substrate. The insertion/extraction of Li+ into the host structure was investigated in 1 M LiClO4-PC with annealed V2O5 films deposited on Ti, Pt and stainless steel substrates. The best electrochemical performances were obtained in the potential range 3.8–2.8 V versus Li/Li+ with V2O5 films deposited onto stainless steel substrate: the reversible capacity reaches after subsequent cycles was about 115 mAh g−1 (rate C/23). In a wider potential range (between 3.8 and 2.2 V versus Li/Li+), V2O5 deposited onto Ti substrate exhibited the higher electrochemical performances (220 mAh g−1 for a rate of C/23).  相似文献   

9.
10.
A designed asymmetric hybrid electrochemical capacitor was presented where NiO and Ru0.35V0.65O2 as the positive and negative electrode, respectively, both stored charge through reversible faradic pseudocapacitive reactions of the anions (OH) with electroactive materials. And the two electrodes had been individually tested in 1 M KOH aqueous electrolyte to define the adequate balance of the active materials in the hybrid system as well as the working voltage of the capacitor based on them. The electrochemical tests demonstrated that the maximum specific capacitance and energy density of the asymmetric hybrid electrochemical capacitor were 102.6 F g−1 and 41.2 Wh kg−1, respectively, delivered at a current density of 7.5 A cm−2. And the specific energy density decreased to 23.0 Wh kg−1 when the specific power density increased up to 1416.7 W kg−1. The hybrid electrochemical capacitor also exhibited a good electrochemical stability with 83.5% of the initial capacitance over consecutive 1500 cycle numbers.  相似文献   

11.
Iron oxide n-Fe2O3 nanowire photoelectrodes were synthesized by thermal oxidation of Fe metal sheet (Alfa Co. 0.25 mm thick) in an electric oven then tested for their photoactivity. The photoresponse of the n-Fe2O3 nanowires was evaluated by measuring the rate of water splitting reaction to hydrogen and oxygen, which is proportional to photocurrent density, Jp. The optimized electric oven-made n-Fe2O3 nanowire photoelectrodes showed photocurrent densities of 1.46 mA cm−2 at measured potential of 0.1 V/SCE at illumination intensity of 100 mW cm−2 from a Solar simulator with a global AM 1.5 filter. For the optimized carbon modified (CM)-n-TiO2 synthesized by thermal flame oxidation the photocurrent density for water splitting was found to increase by two fold to 3.0 mA cm−2 measured at the same measured potential and the illumination intensity. The carbon modified (CM)-n-Fe2O3 electrode showed a shift of the open circuit potential by −100 mV/SCE compared to undoped n-Fe2O3 nanowires. A maximum photoconversion efficiency of 2.3% at applied potential of 0.5 V/Eaoc was found for CM-n-Fe2O3 compared to 1.69% for n-Fe2O3 nanowires at higher applied potential of 0.7 V/Eaoc. These CM-n- Fe2O3 and n- Fe2O3 nanowires thin films were characterized using photocurrent density measurements under monochromatic light illumination, UV-Vis spectra, X-ray diffraction (XRD) and scanning electron microscopy (SEM).  相似文献   

12.
The monoclinic-type Li3V2(PO4)3 cathode material was synthesized via calcining amorphous Li3V2(PO4)3 obtained by chemical reduction and lithiation of V2O5 using oxalic acid as reducer and lithium carbonate as lithium source in alcohol solution. The amorphous Li3V2(PO4)3 precursor was characterized by using TG–DSC and XPS. The results showed that the V5+ was reduced to V3+ by oxalic acid at ambient temperature and pressure. The prepared Li3V2(PO4)3 was characterized by XRD and SEM. The results indicated the Li3V2(PO4)3 powder had good crystallinity and mesoporous morphology with an average diameter of about 30 nm. The pure Li3V2(PO4)3 exhibits a stable discharge capacity of 130.08 mAh g−1 at 0.1 C (14 mA g−1).  相似文献   

13.
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   

14.
LiV3O8, synthesized from V2O5 and LiOH, by heating of a suspension of V2O5 in a LiOH solution at a low-temperature (100-200 °C), exhibits a high discharge capacity and excellent cyclic stability at a high current density as a cathode material of lithium-ion battery. The charge-discharge curve shows a maximum discharge capacity of 228.6 mAh g−1 at a current density of 150 mA g−1 (0.5 C rate) and the 100 cycles discharge capacity remains 215 mAh g−1. X-ray diffraction indicates the low degree of crystallinity and expanding of inter-plane distance of the LiV3O8 phase, and scanning electronic microscopy reveals the formation of nano-domain structures in the products, which account for the enhanced electrochemical performance. In contrast, the LiV3O8 phase formed at a higher temperature (300 °C) consists of well-developed crystal phases, and coherently, results in a distinct reduction of discharge capacity with cycle numbers. Thus, an enhanced electrochemical performance has been achieved for LiV3O8 by the soft chemical method via a low-temperature heating process.  相似文献   

15.
Copper indium disulfide (CuInS2) thin films have been successfully prepared on Ni substrates using a novel one-step potentiostatic electrodeposition combined with a potassium hydrogen phthalate (C8H5KO4) complexing agent, accompanied by annealing at 350 °C. Electrodeposition in the solution of Cu and In salts and sodium thiosulfate (Na2S2O3) containing an adequate concentration of C8H5KO4 (e.g., [C8H5KO4]=23 mM) provides thin films comprised of a CuInS2 single phase as the bulk composition, without forming CuxS secondary phases. In addition to the effect on bulk-phase compositions, the adjustment of [C8H5KO4] causes variation in morphology and atomic composition of the film surface. The surface states of the films change from the Cu-rich rough surface at low [C8H5KO4] (15 mM) to the In-rich smooth surface at high [C8H5KO4] (23 mM). The higher [C8H5KO4] induces the grains constructing the film to interconnect and form a densely packed CuInS2 film without voids and pinholes. The single-phase and void-free CuInS2 film shows a band gap of 1.54 eV, satisfying the requirement of the absorber layers in solar cells. The electrical properties tests denote its n-type conductivity with a resistivity of 9.6×10−5 Ω cm, a carrier concentration of 2.9×1021 cm−3 and a carrier mobility of 22.2 cm2 V−1 s−1.  相似文献   

16.
A dense membrane of Ce0.9Gd0.1O1.95 on a porous cathode based on a mixed conducting La0.6Sr0.4Co0.2Fe0.8O3−δ was fabricated via a slurry coating/co-firing process. With the purpose of matching of shrinkage between the support cathode and the supported membrane, nano-Ce0.9Gd0.1O1.95 powder with specific surface area of 30 m2 g−1 was synthesized by a newly devised coprecipitation to make the low-temperature sinterable electrolyte, whereas 39 m2 g−1 nano-Ce0.9Gd0.1O1.95 prepared from citrate method was added to the cathode to favor the shrinkage for the La0.6Sr0.4Co0.2Fe0.8O3−δ. Bi-layers consisting of <20 μm dense ceria film on 2 mm thick porous cathode were successfully fabricated at 1200 °C. This was followed by co-firing with NiO–Ce0.9Gd0.1O1.95 at 1100 °C to form a thin, porous, and well-adherent anode. The laboratory-sized cathode-supported cell was shown to operate below 600 °C, and the maximum power density obtained was 35 mW cm−2 at 550 °C, 60 mW cm−2 at 600 °C.  相似文献   

17.
Li3V(2 − 2x/3)Mgx(PO4)3/C (x = 0, 0.15, 0.30, 0.45) composites have been synthesized by the sol-gel assisted solid state method, using adipic acid C6H10O4 (hexanedioic acid) as carbon source. The particle size of the composites is ∼1 μm. During the pyrolysis process, Li3V(2 − 2x/3)Mgx(PO4)3/C network structure is formed. The effect of Mg2+ doped on the electrochemical properties of Li3V2(PO4)3/C positive materials has been studied. Li3V1.8Mg0.30(PO4)3/C as the cathode materials of Li-ion batteries, the retention rate of discharge capacity is 91.4% (1 C) after 100 cycles. Compared with Li3V2(PO4)3/C, Li3V(2 − 2x/3)Mgx(PO4)3/C composites have shown enhanced capacity and retention rate capability. The long-term cycles and ex situ XRD tests disclose that Li3V1.8Mg0.30(PO4)3 exhibits higher structural stability than the undoped system.  相似文献   

18.
Al2O3 was synthesized using the sol-gel process with aluminum isopropoxide as the precursor and primary distilled water as the solvent. Nickel and cobalt metal powders were used to increase the strength of the membranes. The Al2O3-based membranes were prepared using HPS following a mechanical alloying process. The phase transformation, thermal evolution, surface and cross-section morphology of Al2O3 and Al2O3-based membranes were characterized by XRD, TG-DTA and FE-SEM. The hydrogen permeation of Al2O3-based membranes was examined at 300–473 K under increasing pressure. Hydrogen permeation flux through an Al2O3-20wt%Co membrane was obtained to 2.36 mol m−2 s−1. Reaction enthalpy was calculated to 4.5 kJ/mol using a Van’t Hoff’s plot.  相似文献   

19.
R.R. Sawant 《Solar Energy》2010,84(7):1208-1215
Cadmium indium sulphide (CdIn2S4) electrodes have been prepared onto the preheated fluorine doped tin oxide (FTO) coated glass and stainless steel (SS) substrates at optimized deposition conditions by using spray pyrolysis. Influence of substrates on the photoelectrochemical (PEC) performance has been carried out using cell configuration n-CdIn2S4/1 M (NaOH + Na2S + S)/C for studying the current-voltage (I-V), photovoltaic output, photovoltaic rise and decay, photo and spectral responses and capacitance-voltage (C-V) characteristics. The junction ideality factor in dark (nD) and light (nL), series and shunt resistances (Rs and Rsh), fill factor (FF) and efficiency (η) for the cell have been estimated. The measured fill factor (FF) and cell efficiency (η) of the cells are found to be 0.47%, 0.38%, and 1.06%, 0.38% for FTO and SS substrates respectively. The Energy band diagram of band bending has been constructed using the physical parameters estimated from Mott-Schottky plots. Mott-Schottky plots shows the flat-band potential (Vfb) of CdIn2S4 films to be −1.15 V/SCE and −0.90 V/SCE on FTO and SS substrates respectively.  相似文献   

20.
In an effort to improve the performance of SUS 430 alloy as a metallic interconnect material, a low cost and Cr-free spinel coating of NiMn2O4 is prepared on SUS 430 alloy substrate by the sol-gel method and evaluated in terms of the microstructure, oxidation resistance and electrical conductivity. A oxide scale of 3-4 μm thick is formed during cyclic oxidation at 750 °C in air for 1000 h, consisting of an inner layer of doped Cr2O3 and an outer layer of doped NiMn2O4 and Mn2O3; and the growth of Cr2O3 and formation of MnCr2O4 are depressed. The oxidation kinetics obeys the parabolic law with a rate constant as low as 4.59 × 10−15 g2 cm−4 s−1. The area specific resistance at temperatures between 600 and 800 °C is in the range of 6 and 17 mΩ cm2. The above results indicate that NiMn2O4 is a promising coating material for metallic interconnects of the intermediate temperature solid oxide fuel cells.  相似文献   

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