Reminiscences on the discovery of electrochromic phenomena in transition metal oxides

It has long been known that transition metal oxides of the types WO₃, MoO₃, TiO₂, V₂O₅, etc., show considerable variation in stoichiometry, and that very often the non-stoichiometric compounds are characterized by strong coloration. This observation led to the fabrication of highly disordered thin films of some of these oxides—ones that showed strong coloration upon optical excitation. Back in the 1960s, there was considerable interest in optically bistable phenomena for high-density information recording, and these oxide films were investigated for that purpose. However, the difficulty encountered in the bleaching process led to the proposition that the optically induced color centers could be bleached by an electric field. Subsequent experiments clearly demonstrated that it was not only possible to form color centers by optical excitation and to bleach them by an electric field, but that it was possible to color and bleach by an electric field alone by simply reversing the polarity. This constituted the first successful demonstration of eletrochromic phenomena in thin films of transition metal oxides. This was quickly followed by the development of various innovative device structures for practical application. In this paper, an attempt will be made to reminisce the discovery of the electrochromic phenomena in this type of material, ultimately leading to the current state of this technology.     

Opportunities and challenges in science and technology of WO3 for electrochromic and related applications

Since the discovery of the electrochromic (EC) effect in transition metal oxides in the mid-1960s, intense research and development work spanning four decades has led to many exciting developments in the science and technology of this class of materials. Tungsten oxide (WO₃) has emerged as one of the key materials, not only for EC devices, but also for many other related applications. After many years of technology development efforts, WO₃-based EC “smart windows” have finally emerged as a viable commercial product. In spite of enormous progress being made on the structural, electrical, and optical properties of amorphous and crystalline WO₃, a detailed understanding of the EC effect in this material still remains somewhat qualitative. Although theoretical models based on intervalence charge transfer and polaron formation have been widely accepted, these models are still unable to explain some of the experimental results on the coloration phenomena. The coloration in WO₃ is a structure-sensitive phenomenon, and excess electrons can be either localized or delocalized. The presence of structural defects such as oxygen vacancies, impurities, and degree of disorder plays a crucial role in determining the coloration efficiency. Although significant progress has been made in recent years on the calculation of electronic structure and defect properties of both amorphous and crystalline WO₃, the structural complexity of the material presents many challenges and opportunities for theoretical computation. The unique ability to induce bistable optical and electrical properties in WO₃ by a variety of excitation sources has led to many devices of significant technological interest. Some of the applications currently being pursued include the photoelectrochemical cell for solar energy conversion and storage; photoelectrochemical splitting of water to generate hydrogen; chemical and biological sensors based on the gasochromic effect; photo- and electrocatalysts for a variety of chemical reactions; demonstration of high-temperature (91 K) superconductivity in WO₃ doped with H, Na, and K; synthesis of a new class of hybrid organic/inorganic (WO₃) materials; and application in ultra-high-resolution electron beam lithography. The emergence of nanostructured WO₃ in recent years will undoubtedly provide new opportunities and significant impact to many of these technologies. This paper presents a brief overview of some of the key research issues the author believes will impact the science and technology of this exciting material.     

Optical indices of lithiated electrochromic oxides

Optical indices have been determined for thin films of several electrochromic oxide materials. One of the most important materials in electrochromic devices, WO₃, was thoroughly characterized for a range of electrochromic states by sequential injection of Li ions. Another promising material, Li_0.5Ni_0.5O, was also studied in detail. Less detailed results are presented for three other common lithium-intercalating electrochromic electrode materials: V₂O₅, LiCoO₂, and CeO₂–TiO₂. The films were grown by sputtering, pulsed laser deposition (PLD) and sol–gel techniques. Measurements were made using a combination of variable-angle spectroscopic ellipsometry and spectroradiometry. The optical constants were then extracted using physical and spectral models appropriate to each material. Optical indices of the underlying transparent conductors, determined in separate studies, were fixed in the models of this work. The optical models frequently agree well with independent physical measurements of film structure, particularly surface roughness by atomic force microscopy. Inhomogeneity due to surface roughness, gradient composition, and phase separation are common in both the transparent conductors and electrochromics, resulting sometimes in particularly complex models for these materials. Complete sets of data are presented over the entire solar spectrum for a range of colored states. These data are suitable for prediction of additional optical properties such as oblique transmittance and design of complete electrochromic devices.     

The role of transition metal oxides in the decomposition and explosion of arylammonium perchlorates

The influence of MnO₂, CuO, and NiO on the thermal decomposition and explosivity of arylammonium perchlorates has been studied by differential thermal analysis (DTA) and explosive sensitivity measurements. The metal oxides considerably sensitize both decomposition and explosion and the sensitizing effect is in the order NiO < CuO < MnO₂. The accelerated decomposition or explosion seems to occur via the formation of an intermediate, metal perchlorate arylamine complex. The experimental evidence for the mechanism put forward has been included.     

Low-temperature flue gas denitration with transition metal oxides supported on biomass char

Several transition metals (Mn, Ce, V and Fe) were loaded on nitric acid modified biomass char (BC) using an impregnation method for the selective catalytic reduction (SCR) of NO with NH₃ at low-temperature. The series of prepared catalysts were characterized by BET, SEM, FT-IR and XRD. Results showed the sequence of NO conversion within the temperature of 125–225 °C was Mn/BC > Ce/BC > V/BC > Fe/BC > BC, and Mn/BC exhibited the highest NO conversion of 87.6% at 200 °C. BC supports provided high surface area, which could contribute to the better dispersion of transition oxides on biomass char, revealing rich oxygen containing groups. Besides, the BC worked not only as a promising support, but also provided high activity adsorption sites for NH₃ and conducted as oxidizing agent for NO due to the existence of graphite crystallite structure. Owing to the existence of “fast SCR” reaction process, the transition metal oxides supported on BC catalysts exhibited superior denitration efficiency in low temperature.     

Opportunities and challenges for biodiesel fuel

Fossil fuel resources are decreasing daily. As a renewable energy, biodiesel has been receiving increasing attention because of the relevance it gains from the rising petroleum price and its environmental advantages. This review highlights some of the perspectives for the biodiesel industry to thrive as an alternative fuel, while discussing opportunities and challenges of biodiesel. This review is divided in three parts. First overview is given on developments of biodiesel in past and present, especially for the different feedstocks and the conversion technologies of biodiesel industry. More specifically, an overview is given on possible environmental and social impacts associated with biodiesel production, such as food security, land change and water source. Further emphasis is given on the need for government’s incentives and public awareness for the use and benefits of biodiesel, while promoting policies that will not only endorse the industry, but also promote effective land management.     

Elucidation of the electrochromic mechanism of nanostructured iron oxides films

Nanostructured hematite thin films were electrochemically cycled in an aqueous solution of LiOH. Through optical, structural, morphological, and magnetic measurements, the coloration mechanism of electrochromic iron oxide thin films was elucidated. The conditions for double or single electrochromic behavior are given in this work. During the electrochemical cycling, it was found that topotactic transformations of hexagonal crystal structures are favored; i.e. α-Fe₂O₃ to Fe(OH)₂ and subsequently to δ-FeOOH. These topotactic redox reactions are responsible for color changes of iron oxide films.     

Microalgal biodiesel in China: Opportunities and challenges

With rapid economic development, energy consumption in China has tripled in the past 20 years, exceeding 2.8 billion tons of standard coal in 2008. The search for new green energy as substitutes for nonrenewable energy resources has become an urgent task. Biodiesel is one of the most important bioenergy sources. According to the Mid- and Long-term Development Plan for Renewable Energy in China, the consumption of biodiesel in China will reach 0.2 million tons in 2010 and 2.0 million tons in 2020. However, large-scale production of biodiesel is restricted by the limited sources of raw materials. Microalgal oil is a prospective raw material for biodiesel production. Development of technology for the production and commercialization of biodiesel from microalgae has become a hot topic in the field of bioenergy and CO₂ emission mitigation. Biodiesel from microalgae can be produced at laboratory-scale, but the cost is too high. Few studies on the commercialization of the technology of producing biodiesel from microalgae have been reported. In this review, recent progress on the research and development of biodiesel from microalgae that have resulted in scientific breakthroughs and innovation in engineering in China are introduced. The existing challenges are also discussed. Based on a detailed analysis, several novel strategies on commercial biodiesel production from microalgae are proposed.     

Coal conversion technology: Opportunities and challenges

Coal conversion is currently not economically viable and its commercialization is not advisable. Both liquefaction and gasification for converting coal to synfuels are hydrogen-enrichment processes. The theoretical yield and efficiency of coal conversion are constrained by hydrogen stoichiometry and cannot be improved through research. Coal conversion is capitalintensive, with capital charges ranging from 40 to over 60% of the total cost. Hydrogen generation and gasification are particularly expensive but may be amenable to cost reduction through research.Coal conversion is most promising for transportation fuels, particularly high-octane gasoline and diesel fuel. Development of utility centers to provide steam, fuel, and electricity to industrial complexes and to commercial and residential communities through cogeneration could soon make coal conversion technology economically viable in some areas.Research efforts should concentrate on generating and testing novel ideas in bench-scale units. Proven ideas can be further developed on a large scale as needed. For large-scale engineering studies, the unit operations approach can be employed without tying the research to a specific process.     

Enhanced hydrogen storage properties and mechanisms of magnesium hydride modified by transition metal dissolved magnesium oxides

Magnesium hydride (MgH₂) is a promising on-board hydrogen storage material due to its high capacity, low cost and abundant Mg resources. Nevertheless, the practical application of MgH₂ is hindered by its poor dehydrogenation ability and cycling stability. Herein, the influences and mechanisms of thin pristine magnesium oxide (MgO) and transition metals (TM) dissolved Mg(TM)O layers (TM = Ti, V, Nb, Fe, Co, Ni) on hydrogen desorption and reversible cycling properties of MgH₂ were investigated using first-principles calculations method. The results demonstrate that either thin pristine MgO or Mg(TM)O layer weakens the MgH bond strength, leading to the decreased structural stability and hydrogen desorption energy of MgH₂. Among them, the Mg(Nb)O layer exhibits the most pronounced destabilization effect on MgH₂. Moreover, the Mg(Nb)O layer presents a long-acting confinement effect on MgH₂ due to the stronger interfacial bonding strength of Mg(Nb)O/MgH₂ and the lower brittleness of Mg(Nb)O itself. Further analyses of electronic structures indicate that these thin oxide layers coating on MgH₂ surface reduce the bonding electron number of MgH₂, which essentially accounts for the weakened MgH bond strength and enhanced hydrogen desorption properties of modified MgH₂ systems. These findings provide a new avenue for enhancing the hydrogen desorption and reversible cycling properties of MgH₂ by designing and adding suitable MgO based oxides with high catalytic activity and low brittleness.     

Nanostructured mixed transition metal oxides for high performance asymmetric supercapacitors: Facile synthetic strategy

Exceptionally simple and cost-effective solid-state method is reported for the synthesis of different mixed transition metal oxides (MTMOs) including FeCo₂O₄, MnCo₂O₄ and ZnCo₂O₄ with unique nanostructures. The morphological analysis show that MTMOs possess distinct nanostructures such as tetragonal, spherical nanoparticles and hexagonal nanosheets. Furthermore, these MTMOs showed excellent supercapacitive properties with specific capacitances of 660–1263 F/g at current density of 2 A/g. Asymmetric capacitor was fabricated with FeCo₂O₄ as positive and activated carbon as negative electrode which exhibits a specific capacitance of 88 F/g with energy density of 24 Wh/kg (1.1 mWh/cm³) and cycle life (93%) over 5000 cycles.     

Opportunities and challenges for renewable energy policy in China

Renewable energy is the inevitable choice for sustainable economic growth, for the harmonious coexistence of human and environment as well as for the sustainable development. Government support is the key and initial power for developing renewable energy. In this article, an overall review has been conducted on renewable energy development policy (including laws and regulations, economic encouragement, technical research and development, industrialized support and government model projects, etc.) in China. On this basis, a systematic analysis has been conducted on the disadvantages of renewable energy development policy. On the point of long-term effective system for renewable energy development, a series of policy advice has been offered, such as strengthening the policy coordination, enhancing regional policy innovation, echoing with clean development mechanism, implementing process management, constructing market investment and financing system. It is expected that the above advices could be helpful to ever-improvement of renewable energy development policy.     

3种过渡金属氧化物对生物质微波快速催化热解产物的影响

以3种过渡金属氧化物Fe2O3,Co3O4,NiO为催化剂,HZSM-5为载体,在微波反应器中对3种典型生物质原料松木、水曲柳和玉米芯快速催化热解。对气、液、固3相热解产物的产率计算结果表明,松木和水曲柳的热解液相产率均比玉米芯高8%左右,Co3O4/HZSM-5有利于液相产率提高,最高可达45.4%(水曲柳)。对液相成分的GC-MS分析表明,所用催化剂均对生物质原料具有良好的脱氧效果,可降低液相产物中酸、醛、酮含量。各催化剂均能大幅提高芳香族化合物产率,其中Co3O4/HZSM-5作用最为明显,最高可达49.61%(松木);且均能促进G型酚与S型酚生成结构更稳定的H型酚,NiO/HZSM-5作用尤为明显,最高产率可达31.64%(玉米芯),有利于产物的富集;Fe2O3/HZSM-5可促进定向热解,对糠醛产率具有较为明显的提高作用,其中玉米芯糠醛产率高达13.61%。     

Renewable energy in the Palestinian Territories: Opportunities and challenges

The Palestinian Territories relies on Israel for 100% of its fossil fuel imports and for 87% of its electricity imports. Total energy consumption in the Palestinian Territories is the lowest in the region and costs more than anywhere else in the Middle East. The purpose of this paper is to present the current energy situation in the Palestinian Territories, evaluate the potential of renewable energies in meeting part of the energy demand and discuss the challenges and benefits of using these types of energies. It is shown that the main renewable energy sources in the Palestinian Territories are solar, wind and biomass. Using the available renewable energy sources in the Palestinian Territories may significantly decrease the energy reliance on neighboring countries and improve the Palestinian population's access to energy. It is estimated that solar sources have the potential to account for 13% of electricity demand and wind energy for 6.6%. The conversion of animal waste into biogas has the potential to meet the needs of 20% of the rural population. The conversion of unused agricultural residue into biodiesel could replace 5% of the imported diesel.     

Current status of renewable energy in Nepal: Opportunities and challenges

Energy is indispensible in modern society and is one of the most important components of socio-economic development. Nepal is one of the least developed countries with more than 80% of its population residing in rural communities. Per capita energy usage – often viewed as a key index of the development – in the country is far less than the global average per capita energy usage. The energy sector is dominated by the traditional energy sources such as fuel woods, crop residues and animal dung mainly for domestic usage contributing to about 86% of the national energy consumption. Currently 40% of the population has access to electricity, and the rural electrification accounts for only 29%. The majority of rural populations are meeting their energy needs by burning biomass in traditional stoves which has several environmental and public health issues. Nearly all fossil-derived fuels consumed in the country are imported in a refined form, and the perpetual increase in petroleum imports has adversely impacted the existing fragile economy of the country. Despite a huge potential in harnessing various renewable energy resources such as hydropower, solar power, wind energy and biofuels/bioenergy, these resources have not been sustainably captured due to geographical, technical, political and economical reasons. This paper presents a brief account of Nepal's renewable energy resources and the current status of various renewable energy technologies (RETs) such as micro-hydro, solar power, wind energy, biofuel/bioenergy, improved cook stoves, and improved water mill. It also highlights the opportunities and barriers for the development of RETs. Finally this paper presents some recommendations for the promotion, development and implementation of RETs in the country.     

Effects of transition metal oxides on the densification of thin-film GDC electrolyte and on the performance of intermediate-temperature SOFC

Transition metal oxides (FeO_1.5 and CoO) were added to Gd-doped ceria (Gd_0.1Ce_0.9O_2−δ, GDC) powder for preparing the thin-film electrolyte used in the anode-supported intermediate-temperature solid oxide fuel cell (SOFC). NiO–GDC anode substrate in a weight ratio of 65:35 was fabricated by the tape-casting method. Thin-film electrolyte was fabricated on the pre-sintered anode substrate by screen-printing method and then co-sintered to form the electrolyte/anode bilayer. The cathode, which is made of La_0.6Sr_0.4Fe_0.8Co_0.2O₃ and GDC (LSCF–GDC) in a weight ratio of 50:50, was screen-printed on the thus-prepared electrolyte surface and sintered to form a complete single cell. The effects of transition metal oxides on the densification of thin-film GDC electrolyte and on the performance of intermediate-temperature SOFC were studied. Results showed that the densification temperature of thin-film GDC electrolyte could not be further reduced by modifying it with transition metal oxides (FeO_1.5 and CoO) as sintering aids. Both the addition of Fe and Co to GDC enhanced the p-type conductivity of the electrolyte resulting in decreased ohmic resistance. However, they played different effects on the polarization behavior of the cells. Fe-loading decreased the single cell polarization resistance, thus greatly enhancing the charge-transfer process below 600 °C. At 500 °C, the charge-transfer resistance of the single cell with Fe-loaded GDC electrolyte is only 78% of that of the cell with pure GDC electrolyte. Conversely, Co-loading inhibited the charge-transfer process in the whole testing temperature range. Thus, it can be concluded that Fe-loaded GDC electrolyte is a promising electrolyte material for intermediate- and low-temperature SOFC.     

Synthesis and photocatalytic properties of CdS-intercalated metal oxides

Photocatalytic properties for hydrogen production were investigated on layered titanium compounds intercalating CdS in the interlayer, which were prepared by direct cation exchange reactions and sulfurization processes. The photocatalytic activity of the compounds intercalating CdS was superior to those of simple CdS and the physical mixture of CdS and metal oxides. The improvement might be attributed to the formation of microheterjunctions between the CdS nanoparticles and the layers of oxides. The activity was also enhanced by the substitution of Nb for partial Ti in K₂Ti₄O₉, which led to the increase in CdS content in the interlayer and the rapid transport of photogenerated electrons through the layer of metal oxide.     

静电纺丝法制备TMO/C复合纳米纤维在锂离子电池负极材料中的应用进展

过渡金属氧化物(TMO)因其极高的理论比容量被认为是代替石墨成为锂离子电池负极材料的最佳选择之一,但是在充放电过程中的过度体积膨胀以及较差的导电性能限制了其进一步发展.将TMO材料与碳材料复合,既能满足储锂容量需求,又能避免充放电过程中过度体积膨胀.通过对近期相关文献的调研,对以静电纺丝技术为基础制备的TMO/C混合材...     

Optical properties of metal oxides based nanofluids

The purpose of this research is to experimentally investigate optical behavior of alumina and titania nanofluids. In this study, classical theories such as, Rayleigh, Maxwell–Garnett and Lambert–Beer's approaches are used for analytical analysis. The effect of surfactant on stability of nanofluids has been examined. Experiment is conducted for two volume concentrations of 0.1% to 0.3% v/v for the optical properties. Both experimental and analytical analyses were used to obtain these properties of nanofluids. Extinction coefficient and refractive index of TiO₂ nanofluids are found higher than Al₂O₃ nanofluids in visible region of light for all concentrations. Results of this work will be very helpful in analyzing direct absorption solar collectors using alumina and titania nanofluids.     

也谈入世后对电力行业的机遇与挑战

加入WTO电力工业将面临严峻的挑战 ,电力市场的垄断将被打破 ,竞争的结果 ,对企业管理、电能质量和电价都将有深刻的影响 ,只要我们适时抓住机遇 ,重视人才培养 ,提高科技水平 ,加快改革开放 ,促进电力工业发展 ,就能把我国电力行业整体水平提高到能与跨国公司相匹敌 ,甚至也可以走向国际市场。