Plasmonic Octahedral Gold Nanoparticles of Maximized Near Electromagnetic Fields for Enhancing Catalytic Hole Transfer in Solar Water Splitting

Due to their localized surface plasmon resonances in visible spectrum, noble metal nanostructures have been considered for improving the photoactivity of wide bandgap semiconductors. Improved photoactivity is attributed to localized surface plasmon relaxations such as direct electron injection and resonant energy transfer. However, the details on the plasmonic solar water splitting through near electromagnetic field enhancement have not been fully understood. Here, the authors report that shape‐controlled gold nanoparticles on wide bandgap semiconductors improve the water‐splitting photoactivity of the semiconductors with over‐bandgap photon energies compared to sub‐bandgap photon energies. It is revealed that hot hole injection into the oxygen evolution reaction potential is the rate‐limiting step in plasmonic solar water splitting. The proposed concept of photooxidation catalysts derived from an ensemble of gold nanoparticles having sharp vertices is applicable to various photocatalytic semiconductors and provides a theoretical framework to explore new efficient plasmonic photoelectrodes.     

Pristine and Al-doped hematite printed films as photoanodes of <Emphasis Type="Italic">p</Emphasis>-type dye-sensitized solar cells

We hereby propose a non-expensive method for the deposition of pure and Al-doped hematite photoanodes in the configuration of thin films for the application of dye-sensitized solar cells (DSSC). The electrodes have been prepared from hematite nanoparticles that were obtained by thermal degradation of a chemical precursor. The particles have been used in the preparation of a paste, suitable for both screen printing and doctor blade deposition. The paste was then spread on fluorine-doped tin oxide (FTO) to obtain porous hematite electrodes. The electrodes have been sensitized using N3 and D5 dyes and were characterized through current/voltage curves under simulated sun light (1 sun, AM 1.5) with a Pt counter electrode. Al-doping of hematite showed interesting changes in the physical and electrochemical characteristics of sensitized photoanodes since we could notice the growth of AlFe₂O₄ (hercynite) as a secondary crystal phase into the oxides obtained by firing the mixtures of two chemical precursors at different molar ratios. Pure and Al-doped hematite electrodes have been used in a complete n-type DSSCs. The kinetics of charge transfer through the interface dye/electrolyte was studied and compared to that of a typical p-type DSSC based on NiO photocathodes sensitized with erythrosine B. The results suggest a potential application of both Fe₂O₃ and Fe₂O₃/AlFe₂O₄ as photoanodes of a tandem DSSC.     

Controllable irregular phenomenon induced by Ag atomic segregation on the melting of (AgPd)561 bimetallic clusters

Here focusing on the very new experimental finding on carbon nanomaterials for solid-state electron mediator applications in Z-scheme photocatalysis, we have investigated different graphene-based nanostructures chemisorbed by various types and amounts of species such as oxygen (O), nitrogen (N) and hydroxyl (OH) and their electronic structures using density functional theory. The work functions of different nanostructures have also been investigated by us to evaluate their potential applications in Z-scheme photocatalysis for water splitting. The N-, O?CN-, and N?CN-chemisorbed graphene-based nanostructures (32 carbon atoms supercell, corresponding to lattice parameter of about 1?nm) are found promising to be utilized as electron mediators between reduction level and oxidation level of water splitting. The O- or OH-chemisorbed nanostructures have potential to be used as electron conductors between H₂-evolving photocatalysts and the reduction level (H⁺/H₂). This systematic study is proposed to understand the properties of graphene-based carbon nanostructures in Z-scheme photocatalysis and guide experimentalists to develop better carbon-based nanomaterials for more efficient Z-scheme photocatalysis applications in the future.     

Cu-doped flower-like hematite nanostructures for efficient water splitting applications

This study reports the successful preparation of Cu-doped hematite (α-Fe₂O₃) flower-like nanostructures with different Cu concentrations on FTO glass substrates using a facile hydrothermal method. The Cu-doped α-Fe₂O₃ flower-like nanostructure combines the advantage of p-type doping with the feature of a flower-like architecture. The prepared nanostructure film was applied as a photocathode in a photoelectrochemical (PEC) water splitting experiment and achieved a significantly improved photocurrent density of −5.34 mA cm⁻² at −0.6 V vs. reversible hydrogen electrode (RHE) for 1 mol% Cu doping. The obtained photocurrent is about 4.85 times higher than that of the pure α-Fe₂O₃ based photoelectrode. The incorporation of Cu into α-Fe₂O₃ results in a dramatic enhancement in the water splitting performance. The enhancement is gained through an improvement in light harvesting and charge carrier separation. The copper-modified α-Fe₂O₃ sample also exhibited an up shift in the conduction band edge potential, which is energetically favorable for the water reduction reaction. This result demonstrated high performance PEC water splitting as a potential route for the production of hydrogen gas using a single Cu-doped α-Fe₂O₃ photoelectrode without the need for other catalysts and hybrid structures.     

Formation of Sn@C Yolk–Shell Nanospheres and Core–Sheath Nanowires for Highly Reversible Lithium Storage

As one promising anode material with high theoretical capacity, metallic tin has attracted much research interest in the field of lithium‐ion batteries. Here, two types of tin/carbon (Sn@C) core–shell nanostructures with inner buffering voids are fabricated from SnO₂ hollow nanospheres via a facile chemical vapor deposition (CVD) method. The crystallinity and surface topography of SnO₂ hollow nanospheres are found to affect the morphology of resultant Sn@C materials. Sn@C yolk–shell nanospheres and core–sheath nanowires are obtained from the as‐prepared SnO₂ and high‐temperature annealed SnO₂ nanospheres, respectively. The unique Sn@C nanostructures can mitigate the agglomeration/pulverization of Sn nanoparticles and electrical disconnection from the current collector caused by the large volume change during the lithium alloying/dealloying process. Both Sn@C yolk–shell and core–sheath nanostructures show stable cycling performance up to 500 cycles with specific capacities of ca. 430 and 520 mA h g^?1, respectively.     

Fluorinated Eu‐Doped SnO2 Nanostructures with Simultaneous Phase and Shape Control and Improved Photoluminescence

Fluorinated Eu‐doped SnO₂ nanostructures with tunable morphology (shuttle‐like and ring‐like) are prepared by a hydrothermal method, using NaF as the morphology controlling agent. X‐ray diffraction, field‐emission scanning electron microscopy, high‐resolution transmission electron microscopy, X‐ray photoelectron spectroscopy, and energy dispersive spectroscopy are used to characterize their phase, shape, lattice structure, composition, and element distribution. The data suggest that Eu³⁺ ions are uniformly embedded into SnO₂ nanocrystallites either through substitution of Sn⁴⁺ ions or through formation of Eu‐F bonds, allowing for high‐level Eu³⁺ doping. Photoluminescence features such as transition intensity ratios and Stark splitting indicate diverse localization of Eu³⁺ ions in the SnO₂ nanoparticles, either in the crystalline lattice or in the grain boundaries. Due to formation of Eu‐F and Sn‐F bonds, the fluorinated surface of SnO₂ nanocrystallites efficiently inhibits the hydroxyl quenching effect, which accounts for their improved photoluminescence intensity.     

Hydrogen on hybrid MoS2/graphene nanostructures

Transition metal dichalcogenides are rising candidates for the replacement of Pt catalysts in water splitting. In this theoretical study we focus on the hydrogen evolution reaction part of this process and on how hydrogen (H) interacts with MoS₂ nanostructures, free‐standing or positioned on a graphene substrate. Density functional theory calculations confirm the stability of such nanostructures and our results for H on several configurations, from 2D infinite monolayers to quasi‐1D MoS₂ ribbons and quasi‐0D MoS₂ flakes, are presented. We calculate the adsorption energy of H atoms on various sites of the MoS₂ nanostructures, notably at Mo and S active edges. Comparing free‐standing and MoS₂/graphene hybrid systems we find that the effect of the support on the adsorption of H on MoS₂ nanostructures is quite significant when the substrate induces strain. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Enhanced photosplitting of water using ultrathin cobalt sulfide nanoflakes-sensitized zinc oxide nanorods array

We report synthesis and characterization of ultrathin cobalt sulfide nanoflakes (CoS_x-NFs) sensitized zinc oxide nanorods (Z-NRs) array based thin films and their implementation as photoanodes for photoelectrochemical (PEC) splitting of water. Cobalt sulfide nanoflakes-sensitized zinc oxide nanorods (CoS_x-NFs/Z-NRs) array based photoanodes were grown on fluorine-doped tin oxide substrate by a simple and versatile electrodeposition method. Maximum conversion efficiency of PEC cell was found 0.37% with a photocurrent density of 0.48 mA/cm² at a bias of 0.3 V/SCE in CoS_x-NFs/Z-NRs-15 (loading of CoS_x-NFs on Z-NRs by cyclic voltammetry for 15 cycles) based photoanodes. The photo-activity is 2.7 times larger than that of Z-NRs array-based photoanode. Experimental results reveal that sensitization by CoS_x-NFs causes red shift in the band gap energy of Z-NRs photoanode. Lower band gap energy, suitable band redox potential, and marked absorption in visible light make CoS_x-NFs/Z-NRs-15 thin films a promising material for photoanodes in PEC cells. A detailed analysis using X-ray diffraction (XRD), UV-Visible (UV-Visible) spectroscopy, field emission scanning electron microscope (FE-SEM), energy-dispersive analysis (EDX), electron impedance spectroscopy (EIS), Mott-Schottky (MS) analysis, applied bias photon-to-current conversion efficiency (ABPE), and incident photon to current conversion efficiency (IPCE) measurements has been carried out to substantiate our observations. The excellent performance of CoS_x-NFs/Z-NRs allows the composite photoelectrode to have many potential applications as a photoanode material for H₂ production, nanoflakes-sensitized solar cells, and UV photodetector.     

Electronic band structure, optical absorption, and photocatalytic activity of iron-doped anatase

Quasi-one-dimensional solid solutions of the composition Ti_{1 ? x} Fe _x O_{2 ? x/2} (0.005 ≤ x ≤ 0.050) with the anatase-type structure and extended aggregates have been prepared by the precursor method. The absorption spectra of the solid solutions have been investigated in the ultraviolet and visible regions, and the photocatalytic activity in the oxidation reaction of hydroquinone in water has been estimated. It has been found that the synthesized solid solutions serve as photocatalysts only under ultraviolet irradiation, and their photoactivity increases with an increase in the dopant concentration. The first-principles calculations of the electronic band structure and optical absorption in iron-doped anatase and rutile have been performed using the pseudopotential method LSDA + U (with the VASP software package). The on-site exchange-correlation parameters have been calibrated in the calculations of the electronic band structure of hematite α-Fe₂O₃ and ilmenite FeTiO₃. It has been shown that, despite the appearance of impurity states within the band gap of anatase and rutile, doping with iron does not cause substantial absorption in the visible region, which correlates with the increase in photocatalytic activity only under ultraviolet irradiation. The most probable cause of the experimentally observed absorption in the visible region is the presence of finely dispersed hematite impurities in the obtained samples.     

Sn and SnO2-graphene composites as anode materials for lithium-ion batteries

Sn and SnO₂-graphene composites were synthesized using hydrothermal process, followed by annealing in Ar/H₂ atmosphere, and characterized using x-ray diffraction, scanning electron microscopy, and transition electron microscopy. The results indicated that the polycrystalline metallic Sn forms nanospheres with a diameter of 100?～?300 nm, while the SnO₂ nanoparticles are much smaller with a size below 15 nm, which adsorb tightly on the surface of graphene sheets. The Sn and SnO₂-gaphene composites showed good electrochemical performance. After 55 charging/discharging cycles, the capacity remains above 440 mAh/g at a cycling rate of 400 mA/g and the coulombic efficiency is 99.1 %. The good electrochemical properties of the composites are partially contributed to the graphene component with good mechanical flexibility and electrical conductivity, which is an excellent carbon matrix for dispersing the Sn and SnO₂ nanostructures and provides the electron transport pathways as well.     

Electron transport in dye-sensitized solar cells based on TiO2 nanowires

Anatase titanium dioxide nanowire arrays were prepared by hydrothermally oxidizing titanium foils in aqueous alkali and transferred onto fluorinated tin oxide(FTO)glass for use as the photoanodes of front side illuminated dye-sensitized solar cells(DSCs).Electrochemical impedance spectroscopy(EIS)measurement was applied to compare the electron transport and recombination properties of DSCs using TiO2nanowire films and TiO2nanoparticle films as photoanodes.It was found that the nanowire array films possess smaller electron transport resistance(Rt)and larger electron diffusion length(Le)in the photoanodes,suggesting that the nanowire arrays can enhance the electron transport rate and have a potential to improve the charge collection efficiency of DSCs.     

Characterization of bismuth–tin–lead and bismuth–tin–lead–cadmium fusible alloys

Microstructure, electrical, mechanical and thermal properties of quenched bismuth–tin eutectic, Rose (Bi₅₀Sn_22.9Pb_27.1) and Wood’s (Bi₅₀Sn_12.5Pb₂₅Cd_12.5) alloys have been investigated using scanning electron microscopy, X-ray diffraction analysis, the double bridge method, the dynamic resonance method, Vickers hardness measurement and thermal analysis. Wood’s alloy (Bi–Pb–Sn–Cd) has low electrical resistivity and melting point but a high elastic modulus and internal friction when compared with the Rose (Bi–Pb–Sn) alloy. The presence of cadmium in Wood’s alloy decreases its melting point and electrical resistivity with an increase in its elastic modulus, which improves the mechanical properties. Wood’s alloy (Bi–Pb–Sn–Cd) has better properties, which make it useful in various applications such as in protection shields for radiotherapy, locking of mechanical devices and welding at low temperature.     

化学气相沉积法中SnO2一维纳米结构的控制生长

以Sn和SnO为源材料，化学气相沉积法中通过控制反应物配比及载气中的氧含量等宏观实验条件，实现了SnO₂一维纳米结构的控制生长，成功获得各种不同横向尺度的SnO₂纳米线、纳米带以及直径连续变化的针状纳米结构. 通过扫描电子显微镜、X射线衍射仪对不同实验条件下所制备的样品进行形貌和晶格结构表征，认为高温生长点附近锡与氧的相对含量是控制SnO₂一维纳米结构生长的关键因素；并在此基础上对SnO₂一维纳米结构的生长机理进行了深入的讨论.     

Effect of lead on microstructure and some physical properties of Sn–Zn–Cd alloy

The effect of lead on the structure, electrical resistivity, internal friction, elastic modulus and thermal properties of Sn₈₁Zn₉Cd₁₀ ternary alloys have been investigated using different experimental techniques with their analysis. In addition, properties of this alloy were compared with other Sn–Zn or Sn–Zn–Cd alloys and commercial solder alloys. It has a higher electrical resistivity, internal friction and lower elastic modulus when compared with Sn–Zn or Sn–Zn alloys with other additions such as Cd, Bi or In. The Sn₆₁Zn₉Cd₁₀Pb₂₀ alloy has a lower melting point, electrical resistivity and internal friction when compared with the commercial Pb–Sn solder alloy, but it has a similar elastic modulus.     

Flame synthesis of WO3 nanotubes and nanowires for efficient photoelectrochemical water-splitting

Tungsten trioxide (WO₃) is a technologically important material for photoelectrochemical (PEC) water-splitting for the solar production of hydrogen fuel from water. For PEC water-splitting, high aspect ratio WO₃ nanostructures such as nanowires (NWs) and nanotubes (NTs) are superior to planar WO₃ films because they orthogonalize the directions of light absorption (along the long axis) and charge transport (across the short radius), leading to both efficient light absorption and charge carrier collection. However, PEC water-splitting requires the growth of WO₃ on delicate transparent conducting oxide (TCO) substrates that cannot tolerate high temperature processing. To date, the large-scale, rapid, economical synthesis of high aspect ratio WO₃ nanostructures on these delicate TCO substrates remains a major challenge. Previously, we synthesized WO₃ NW arrays by a rapid, atmospheric and scalable flame vapor deposition (FVD) method, in which a flame oxidizes and evaporates tungsten metal to produce tungsten oxide vapors that condense onto a colder substrate in the form of NWs. Nevertheless, at substrate temperatures low enough to ensure the health of the TCO, the growth of WO₃ NW arrays was non-uniform and sparse due to limitations of the experimental design. Herein, we significantly improve the FVD design to grow uniform and densely packed WO₃ nanostructures on TCO substrates, thereby enabling the application of these WO₃ nanostructures to PEC water-splitting. The morphology of the nanostructures varied from densely packed multi-shell NTs and single-shell NTs to NWs as we increased the substrate temperature in the range 530–700 °C. Importantly, the WO₃ NTs synthesized by FVD had higher areal number density and longer length than state-of-the-art WO₃ NW photoanodes grown by chemical vapor deposition and hydrothermal methods, resulting in stronger light absorption and superior PEC water-splitting performance. Thus, in addition to being scalable, rapid and economical, the FVD method also synthesizes materials of high quality.     

Facile preparation of SnC2O4 nanowires for anode materials of a Li ion battery

A simple method of creating densely-packed nanostructures of functional metal oxides is attractive, but it has always been a challenge. Here, we synthesize well-distributed nanostructures of Sn complexes (SnC₂O₄ and SnO₂) via a simple chemical anodization technique followed by annealing. Chemical anodization of Sn surface in oxalic acid, using various organic solvents, provides one-dimensional nanostructures of SnC₂O₄. Length and packing density were precisely controlled by several parameters: solubility of oxalic acid, dielectric constant of organic solvents, and the ion transfer of proton and oxalate anion. Further thermal decomposition converts the SnC₂O₄ nanowires into SnO₂ nanowires, maintaining the nanostructure form in the process. In addition, we expect that the mixture of SnC₂O₄ and SnO₂ nanowires synthesized by this approach might be potential alternative anode materials for prompt charging and discharging Li ion batteries.     

Structural, optical and electrical characterization of antimony-substituted tin oxide nanoparticles

Antimony-doped tin oxide (ATO) nanostructures were prepared using chemical precipitation technique starting from SnCl₂, SbCl₃ as precursor compounds. The antimony composition was varied from 5 to 20 wt%. The lower resistance was observed at composition of Sn:95 and Sb:05, when compared with undoped and higher doping concentration of antimony. The average crystalline size of undoped and doped tin oxide was calculated from the X-ray diffraction (XRD) pattern and found to be in the range of 30-11 nm and it was further confirmed from the transmission electron microscopy (TEM) studies. The scanning electron microscopy (SEM) analysis showed that the nanoparticles agglomerates forming spherical-shaped particles of few hundreds nanometers. The samples were further analyzed by energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and electrical resistance measurements.     

Electronic, magnetic and transport properties of Co2TiZ (Z=Si, Ge and Sn): A first-principle study

We have studied the electronic structure, magnetic and transport properties of some Co based full Heusler alloys, namely Co₂TiZ (Z=Si, Ge and Sn), in the frame work of first-principle calculations. The calculations show that Co₂TiZ (X=Si, Ge and Sn) are to be half-metallic compounds with a magnetic moment of 2 μ_B, well consistent with the Slater-Pauling rule. The electronic structure results reveal that Co₂TiZ has the high density of states at the Fermi energy in the majority-spin state and show 100% spin polarization. Our results also suggest that both the electronic and magnetic properties in these compounds are intrinsically related to the appearance of the minority-spin gap. The origin of energy gap in the minority-spin states is discussed in terms of the electron splitting of Z (Z=Si, Ge and Sn) and 3d Co atoms and also the d-d hybridization between the Co and Ti atoms. The transport properties of these materials are discussed on the basis of Seebeck coefficients, electrical conductivity coefficients and thermal conductivity coefficients.