Enhancing the photoelectrochemical performance of p-silicon through TiO2 coating decorated with mesoporous MoS2

MoS₂ is a promising electrocatalyst for hydrogen evolution reaction and a good candidate for cocatalyst to enhance the photoelectrochemical (PEC) performance of Si-based photoelectrode in aqueous electrolytes. The main challenge lies in the optimization of the microstructure of MoS₂, to improve its catalytic activity and to construct a mechanically and chemically stable cocatalyst/Si photocathode. In this paper, a highly-ordered mesoporous MoS₂ was synthesized and decorated onto a TiO₂ protected p-silicon substrate. An additional TiO₂ necking was introduced to strengthen the bonding between the MoS₂ particles and the TiO₂ layer. This meso-MoS₂/TiO₂/p-Si hybrid photocathode exhibited significantly enhanced PEC performance, where an onset potential of +0.06 V (versus RHE) and a current density of −1.8 mA/cm² at 0 V (versus RHE) with a Faradaic efficiency close to 100% was achieved in 0.5 mol/L H₂SO₄. Additionally, this meso-MoS₂/TiO₂/p-Si photocathode showed an excellent PEC ability and durability in alkaline media. This paper provides a promising strategy to enhance and protect the photocathode through high-performance surface cocatalysts.     

Enhanced TiO2 photocatalysis by Cu in hydrogen production from aqueous methanol solution

Cu particles have been deposited on TiO₂ by incipient-wetness impregnation followed by low-temperature (400°C) calcination/reduction, and the metallization process leads to significant enhancement in photocatalytic activity of TiO₂ for H₂ production from aqueous methanol solution. The activity exhibits up to 10-fold enhancement at the optimum loading of 1.2 wt% Cu. Spectroscopic studies indicated that the Cu particles were oxidized during reaction to have a valence lower those of thermally oxidized particles, which showed inferior activities. Dissolution of Cu ion in TiO₂ lattice, in contrast, resulted in reduction in photocatalytic activity.     

Interfacial charge transfer and photocatalytic activity in a reverse designed Bi2O3/TiO2 core-shell

In this study, the electronic and photocatalytic properties of core-shell heterojunctions photocatalysts with reversible configuration of TiO₂ and Bi₂O₃ layers were studied. The core-shell nanostructure, obtained by efficient control of the sol-gel polymerization and impregnation method of variable precursors of semiconductors, makes it possible to study selectively the role of the interfacial charge transfer in each configuration. The morphological, optical, and chemical composition of the core-shell nanostructures were characterized by high-resolution transmission electron microscopy, UV-visible spectroscopy and X-ray photoelectron spectroscopy. The results show the formation of homogenous TiO₂ anatase and Bi₂O₃ layers with a thickness of around 10 and 8 nm, respectively. The interfacial charge carrier dynamic was tracked using time resolved microwave conductivity and transition photocurrent density. The charge transfer, their density, and lifetime were found to rely on the layout layers in the core-shell nanostructure. In optimal core-shell design, Bi₂O₃ collects holes from TiO₂, leaving electrons free to react and increase by 5 times the photocatalytic efficiency toward H₂ generation. This study provides new insight into the importance of the design and elaboration of optimal heterojunction based on the photocatalyst system to improve the photocatalytic activity.     

LiMn2O4 electrode prepared by gold–titanium codeposition with improved cyclability

An LiMn₂O₄ electrode was prepared based on mixed-metals (gold–titanium) codeposition method. By this method, titanium oxide is also incorporated into the electroactive film formed on substrate electrode. Formation of titanium oxide on the spinel surface avoids dissolution of Mn from the spinel at elevated temperatures. TiO₂can act as a bridge between the spinel particles to reduce the interparticle resistance and as a good material for the Li intercalation/deintercalation. Thus, electrochemical performance of the LiMn₂O₄ spinel can be improved by the surface modification with TiO₂. This action improves cyclability for lithium battery performance and reduces capacity fades of LiMn₂O₄ at elevated temperatures.     

TiO2-Cu[HgI4]纳米复合材料的制备及其热致变色性能

以TiO₂为载体制备了TiO₂-Cu[HgI₄]纳米复合材料,利用HRTEM、XRD、DSC、UV-Vis等方法对该材料的结构及其热致变色性能进行了研究。研究表明,TiO₂-Cu[HgI₄]纳米复合材料具有较好的热致变色性能,随着nTiO₂/nCu[HgI₄]摩尔比值的增大,其可见光吸收性能增强,相变温度也相应升高。     

石墨烯包封Na3V2(PO4)3用作钠离子电池负极材料的电化学性能探究

具有三维网络结构的NASICON型Na₃V₂(PO₄)₃材料,由于其稳定的电压平台,较高的理论容量(117 mA·h/g),被视为一种具有良好应用前景的钠离子电池负极材料。采用溶剂热和进一步热处理的方式,获得石墨烯包封Na₃V₂(PO₄)₃的复合材料[Na₃V₂(PO₄)₃/G],有效提高了Na₃V₂(PO₄)₃的电子导电性。在0.01～3.00 V电压区间,0.2 C倍率进行测试时,Na₃V₂(PO₄)₃/G复合材料在230圈循环后,其放电比容量保持在100.9 mA·h/g,容量保持率高达68.4%,即使在5 C倍率,其放电比容量仍可达65.2 mA...     

The influence of acid treatment of TiO2 porous film electrode on photoelectric performance of dye-sensitized solar cell

A dye-sensitized solar cell (DYSC) was assembled by adsorbing cis-dithiocyanato-bis (2,2^′-bipyridyl-4,4^′-dicarboxylate) ruthenium (II) onto TiO₂ porous film. The influence of acid treatment of TiO₂ electrode with different kinds and concentrations on the photoelectric performance of DYSC was investigated. It was found that DYSC had better photoelectric performance when the TiO₂ electrode was treated by hydrochloric acid than that by sulfuric acid, nitric acid and phosphoric acid. When the concentration of hydrochloric acid to treat TiO₂ electrode increases from 0 to 0.10 M, the fill factor of DYSC increases, the short-circuit current decreases, the open-circuit photovoltage increases and the absorption amount for TiO₂ porous film to dye molecules decreases. The acid treatment of TiO₂ electrode provides useful information on the mechanism of energy conversion of DYSC.     

Roles of various Ni species on TiO2 in enhancing photocatalytic H2 evolution

Low-cost nickels can be used as cocatalyst to improve the performance of photocatalysts, which may be promising materials applied in the field of photocatalytic water splitting. In this study, different nickel species Ni, Ni(OH)₂, NiO, NiO_x, and NiS are used to modified titanium dioxide (P25) to investigate their roles on the photocatalytic hydrogen evolution activities. UV-visible, X-ray diffraction (XRD), Brunner-Emmet-Teller (BET) measurements, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) analysis etc. are employed to characterize the physical and chemical properties of catalysts. The results indicate that all the nickel species can improve the photocatalytic hydrogen production activity of P25. The P25 modified with NiO_x and NiS has more superior photocatalytic hydrogen evolution activities than those modified with other nickel species. The reason for this is that NiO_x and NiS can form p-n junctions with P25 respectively. In addition, NiO_x can be selectively deposited on the active sites of P25 via in situ the photodeposition method and NiS is beneficial for H⁺ reacting with photo-excited electrons.     

Physicochemical properties and photocatalytic hydrogen evolution of TiO2 films prepared by sol–gel processes

Anatase TiO₂ films were obtained on glass substrates using a sol–gel method using titanium isopropoxide as a precursor. The thickness of the film was about 140 nm for one coating, and the thickness is controlled by the number of coating cycles. The spectra of UV-VIS absorption indicated that the absorption edge of the TiO₂ films is ca. 385 nm, corresponding to the band gap energy of 3.20 eV. We obtained TiO₂ films having a high activity for the hydrogen evolution from photocatalytic water cleavage. By loading with 0.3 wt% Pt rate of hydrogen production increases. No influence of film thickness and calcination temperature on the photocatalytic property is observed.     

TiO2纳米薄膜厚度对CdS纳米柱阵列 光电化学性能和稳定性的影响

利用水热合成法在导电玻璃表面上原位生长CdS纳米柱阵列（CdSNRA）,然后通过浸渍提拉法在其表面涂覆TiO₂纳米薄膜,制备CdSNRA@TiO₂异质结复合结构材料。利用扫描电镜、X射线衍射、紫外可见光吸收、拉曼光谱等手段对其形貌和结构进行表征。进一步考察了TiO₂薄膜厚度对CdSNRA@TiO₂复合结构光电极的光电化学性能的影响。结果表明,覆盖50 nm 厚TiO₂层的CdSNRA复合结构光电极在可见光下具有更好的光电性能和稳定性,这归因于CdSNRA核和TiO₂壳之间光生电子和空穴的有效分离。     

Enhanced performance of NiF2/BiVO4 photoanode for photoelectrochemical water splitting

The serious surface charge recombination and fatigued photogenerated carriers transfer of the BiVO₄ photoanode restrict its photoelectrochemical (PEC) water splitting performance. In this work, nickel fluoride (NiF₂) is applied to revamp pure BiVO₄ photoanode by using a facile electrodeposition method. As a result, the as-prepared NiF₂/BiVO₄ photoanode increases the dramatic photocurrent density by approximately 180% compared with the pristine BiVO₄ photoanode. Furthermore, the correlative photon-to-current conversion efficiency, the charge injection, and the separation efficiency, as well as the hydrogen generation of the composite photoanode have been memorably enhanced due to the synergy of NiF₂ and BiVO₄. This study may furnish a dependable guidance in fabricating the fluoride-based compound/semiconductor composite photoanode system.     

In situ growth of a-few-layered MoS2 on CdS nanorod for high efficient photocatalytic H2 production

An ultrathin MoS₂ was grown on CdS nanorod by a solid state method using sulfur powder as sulfur source for photocatalytic H₂ production. The characterization result reveals that the ultrathin MoS₂ nanosheets loaded on CdS has a good contact state. The photoelectrochemical result shows that MoS₂ not only are beneficial for charge separation, but also works as active sites, thus enhancing photocatalytic activity. Compared with pure CdS, the photocatalytic activity of MoS₂ loaded CdS was significantly improved. The hydrogen evolution rate on m(MoS₂): m(CdS) = 1: 50 (m is mass) reaches 542 μmol/h, which is 6 times of that on pure CdS (92 μmol/h). This work provides a new design for photocatalysts with high photocatalytic activities and provides a deeper understanding of the effect of MoS₂ on enhancing photocatalytic activity.     

CuInS2 based thin film photovoltaics

A fabrication process for CuInS₂ thin film solar cells, based on sulfurization of Cu/In bilayers, is described. The process is investigated by in situ energy dispersive X-ray diffraction for phase identification as a function of process time. It is found that Raman spectroscopy is very convenient and reliable in assessing the quality of CuInS₂ produced by this sequential process. Good quality CuInS₂ films efficiently collect charge carriers generated by the incident sunlight. The solar-to-electric conversion efficiency limitations of state-of-the-art CuInS₂ based devices are discussed using a comparison with device simulation. The module design is laid down and arguments for the up-scaling potential of this new type of solar cell are presented.     

Brown coloring electrochromic devices based on NiO–TiO2 layers

Brown coloring electrochromic 5×10 cm² windows with the configuration K-glass/NiO–TiO₂/electrolyte/CeO₂–TiO₂/K-glass have been prepared and characterized by optoelectrochemical techniques (cyclic voltammetry, chronoamperometry and galvanostatic measurements). The electrochromic layers have been prepared by the sol–gel technique. As electrolyte either a 1 M aqueous KOH solution or a newly developed starch-based gel impregnated with KOH have been used. The CeO₂–TiO₂ sol–gel layers sintered at 550 °C have been previously characterized in 1 M aqueous KOH electrolyte as a function of the thickness up to 2000 cycles and showed a highly reversible behavior without any corrosion effect. The NiO–TiO₂ sol–gel layers sintered at 300 °C have been extensively characterized in the same electrolyte up to about 7000 cycles. All windows present a deep brown color characteristic of the presence of Ni³⁺ (NiOOH) species, that is fully reversible for several thousands of cycles with a rather-fast kinetics (<30 s). The transmittance of the bleached state however slowly decreases with cycling (permanent coloration). The full-bleached condition can be nevertheless recovered by applying a negative potential for a long duration. Deeper coloration is usually obtained by cycling the windows galvanostatically with a current density of 20 μA/cm². The lifetime of the windows is however limited because of the degradation of the NiO-based layers due to the not fully reversible exchange of OH⁻ that turns the layers mechanically fragile and leads eventually to their complete removal from the substrate. Windows working satisfactorily up to 7000 and 17 000 cycles have been obtained using aqueous KOH electrolyte and starch KOH gel electrolyte, respectively. Memory tests showed that the devices bleach at the open circuit potential from T=39% (colored state) to about T=50% in 60 min.     

MIL-101(Cr)-NH2/CaCl2复合材料的热化学蓄热性能研究

将金属有机骨架MIL-101(Cr)-NH₂与CaCl₂通过浸渍的方法复合得到MIL-101(Cr)-NH₂/CaCl₂热化学蓄热复合材料。采用X射线衍射分析仪（XRD）、扫描电子显微镜（SEM）、能谱分析（EDS）、全自动比表面积及孔径分析仪以及同步热分析仪（TG-DSC）等分析了复合材料的表观形貌、盐含量、比表面积和蓄热密度等参数。结果显示,复合材料的盐含量为49%,在30℃、32%湿度下的最大吸水量为0.54 g(H₂O)/g(样品),蓄热密度达到了1 204 kJ/kg,并且在经历了17次吸附-解吸循环后,其蓄热密度仅降低了6.5%,表现出优异的循环稳定性,出色的吸附性能表明这一新型复合材料在太阳能蓄热领域具有广阔的应用前景。     

Preparation and electrochemical characteristics of LiNi1/3Mn1/3Co1/3O2 coated with metal oxides coating

LiNi_1/3Mn_1/3Co_1/3O₂ prepared by a spray drying method exhibited poor cyclic performance when it was operated at rates of 0.5C and 2C in 3–4.6 V. A metal oxide (ZrO₂, TiO₂, and Al₂O₃) coating (3 wt%) could effectively improve its cyclic performance at both 0.5C and 2C. Electrochemical impedance spectroscopy (EIS) studies suggested that both the surface resistance and the charge transfer resistance of the bare LiNi_1/3Mn_1/3Co_1/3O₂ significantly increase after 100 cycles, whose origin is mainly related to the change in both the particle surface and electrode morphologies. The presence of a thin metal oxide layer could remarkably suppress the increase in the total resistance (sum of the surface resistance and the charge transfer resistance), which was attributed to the improvement in good cyclic performances.     

Z-scheme CdS/WO3 on a carbon cloth enabling effective hydrogen evolution

Photocatalytic water splitting for hydrogen (H₂) generation is a potential strategy to solve the problem of energy crisis and environmental deterioration. However, powder-like photocatalysts are difficult to recycle, and the agglomeration of particles would affect the photocatalytic activity. Herein, a direct Z-scheme CdS/WO₃ composite photocatalyst was fabricated based on carbon cloth through a two-step process. With the support of carbon cloth, photocatalysts tend to grow uniformly for further applications. The experimental results showed that the H₂ yield of adding one piece of CdS/WO₃ composite material was 17.28 μmol/h, which was 5.5 times as compared to that of pure CdS-loaded carbon cloth material. A cycle experiment was conducted to verify the stability of the as-prepared material and the result demonstrated that the H₂ generation performance of CdS/WO₃ decreased slightly after 3 cycles. This work provides new ideas for the development of recyclable photocatalysts and has a positive significance for practical applications.     

Factors affecting photocatalytic performance through the evolution of the properties due to the phase transition from NaBiO3·2H2O to BiO2–x

The phase transition process of a photocatalytic system from NaBiO₃·2H₂O to BiO_2–x has been investigated to understand the important factors that affect photocatalytic performance in a composite system. It is found that a proper amount of BiO_2–x on the surface of NaBiO₃·2H₂O could effectively suppress the electron/hole recombination and increase the exposed reactive sites for photocatalytic reaction. A fully covered BiO_2–x on NaBiO₃·2H₂O results in a dramatical decrease of photocatalytic degradation of dye. An over long hydrothermal process can result in BiO_2–x with reduced oxygen vacancies, which degrades the photocatalytic activity. Furthermore, the photocatalytic reduction ability of CO₂ conversion has been investigated, indicating that the surface activity to different reactants also directly affects the catalytic performance. The investigation of the gradient phase transition process presents a clear guidance to construct a desired photocatalytic system, in addition to selecting gradient materials with suitable bandgap structure and a morphology with different fraction and distribution of each component. The defect evolution of each component during construction of a composite is also an important factor that should be optimized and considered in making a composite to achieve high photocatalytic efficiency.     

Characterization of MnO2 positive electrode for Fuel Cell/Battery (FCB)

The use of manganese dioxide (MnO₂) as a positive electrode material in Fuel Cell/Battery (FCB) systems is described. A positive electrode containing MnO₂ was fabricated and its performance was evaluated for charge/discharge behavior in three different systems: (i) secondary battery positive electrode, (ii) positive electrode in an alkaline fuel cell, and (iii) positive electrode performance in an FCB system by performing half cell tests. MnO₂ was observed to possess redox capabilities as the positive electrode of a secondary battery when it was subject to charge/discharge cycles. It was found that Mn₃O₄, which inhibits the discharge reaction, was produced during charge/discharge cycles. The I–V characteristics of MnO₂ material were measured to check the feasibility of the fuel cell system by supplying H₂ into the negative electrode and O₂ into the MnO₂ positive electrode, respectively. The MnO₂ electrode showed similar performance to Ni electrode, which was fabricated by using a similar method to the MnO₂ electrode. The MnO₂ electrode also showed that it functioned as an FCB positive electrode, which was confirmed by continued production of current when the O₂ supply was terminated. These results suggest that MnO₂ is a good candidate for an FCB positive electrode material.     

Porous TiO2 thin films synthesized by a spray pyrolysis deposition (SPD) technique and their application to dye-sensitized solar cells

Titanium dioxide (TiO₂) thin films were synthesized on glass substrates from titanium(IV)oxy acetylacetonate 2-butanol solution by a spray pyrolysis deposition (SPD) technique. The films consisted of TiO₂ leaflets and showed the oriented growth along the (2 0 0) direction. The surface area of the film was successfully increased by adding a small amount of aluminum(III) acetylacetonate (AA) in the source solution. This is because AA sublimates easily during the film formation to leave many pores within the film. A dye-sensitized solar cell was constructed with the TiO₂ film which was deposited on the fluorine-doped tin(IV) oxide layer by the SPD technique. The conversion efficiency of the cell was effectively enhanced as high as 3.2% at AA content of 0.6 at% in the source solution, attributing to the fact that the amount of a dye anchored on the surface of TiO₂ layer was the highest at this AA content. Although the conversion efficiency is relatively low, this finding leads to the possibility of an industrial production of a dye-sensitized solar cell in the near future.