Influence of scattering processes on electron quantum states in nanowires

In the framework of quantum perturbation theory the self-consistent method of calculation of electron scattering rates in nanowires with the one-dimensional electron gas in the quantum limit is worked out. The developed method allows both the collisional broadening and the quantum correlations between scattering events to be taken into account. It is an alternative per se to the Fock approximation for the self-energy approach based on Green’s function formalism. However this approach is free of mathematical difficulties typical to the Fock approximation. Moreover, the developed method is simpler than the Fock approximation from the computational point of view. Using the approximation of stable one-particle quantum states it is proved that the electron scattering processes determine the dependence of electron energy versus its wave vector.     

Oxide materials for high temperature thermoelectric energy conversion

Thermoelectric energy conversion can be used to capture electric power from waste heat in a variety of applications. The materials that have been shown to have the best thermoelectric properties are compounds containing elements such as tellurium and antimony. These compounds can be oxidized if exposed to the high temperature air that may be present in heat recovery applications. Oxide materials have better stability in oxidizing environments, so their use enables the fabrication of more durable devices. Thus, although the thermoelectric properties of oxides are inferior to those of the compounds mentioned above, their superior stability may expand potential the high temperature application of thermoelectric energy conversion.In this paper, the thermoelectric properties of promising oxide materials are reviewed. The different types of oxides used for thermoelectric applications are compared and approaches for improving performance through doping are discussed.     

Solar energy conversion with tunable plasmonic nanostructures for thermoelectric devices

The photothermal effect in localized surface plasmon resonance (LSPR) should be fully utilized when integrating plasmonics into solar technologies for improved light absorption. In this communication, we demonstrate that the photothermal effect of silver nanostructures can provide a heat source for thermoelectric devices for the first time. The plasmonic band of silver nanostructures can be facilely manoeuvred by tailoring their shapes, enabling them to interact with photons in different spectral ranges for the efficient utilization of solar light. It is anticipated that this concept can be extended to design a photovoltaic-thermoelectric tandem cell structure with plasmonics as mediation for light harvesting.     

Effect of nanowires in microporous structures on the thermoelectric properties of oxidized Sb-doped ZnO film

Sb-doped ZnO thermoelectric films with microporous structures are fabricated by oxidizing evaporated Zn-Sb thin films in a leaf-like surface. High magnetic field (HMF) and Sb are employed to tune the formation of nanowires and nanorods in the microporous films and conduction type. Nanowire is formed in the film with Sb content of 3.0% and nanorod is formed with 4.6% Sb with the absence of HMF. P-type ZnO films with a wuterzite are formed. The resistivity of the films decreases by two orders of magnitude by increasing Sb content. The resistivity of films decreases 45% and 80% by forming nanowires and nanorods, respectively. The power factor of the nanorod structures increases by two orders of magnitude by comparison with others and reaches to 52.6 μW/m?K². This indicates that the nanorod structures with a higher Sb content are easy to obtain stable p-type semiconductor with a higher power factor.     

Metal ion modulated electron transfer in photosynthetic proteins

Photosynthetic purple bacterial reaction center (RC) proteins are ideal native systems for addressing basic questions regarding the nature of biological electron transfer because both the protein structure and the electron-transfer reactions are well-characterized. Metal ion binding to the RC can affect primary photochemistry and provides a probe for understanding the involvement of local protein environments in electron transfer. The RC has two distinct transition metal ion binding sites, the well-known non-heme Fe(2+) site buried in the protein interior and a recently discovered Zn(2+) site located on the surface of the protein. Fe(2+) removal and Zn(2+) binding systematically affect different electron-transfer steps in the RC. Factors involved in the metal ion alteration of RC electron transfer may provide a paradigm for other biological systems involved in electron transfer.     

Using negative electron affinity diamond emitters to mitigate space charge in vacuum thermionic energy conversion devices

A negative electron affinity (NEA) diamond surface is employed as an emitter electrode in a vacuum thermionic energy conversion device in order to mitigate the negative space charge effect. The motive diagram of an NEA device operating at the virtual saturation point is compared to a similar device with a conventional emitter material operating in the space charge limited regime in order to understand how NEA mitigates space charge. Output current characteristics are calculated for various NEA values, and the results are compared to an ideal (no space charge) model. Increasing the value of the NEA causes the output current characteristic to approach that of the ideal model. Motive diagrams for various values of NEA are calculated and used to explain this phenomenon. It is shown that an NEA device can achieve a maximum output power density equal to the maximum output power density of a similar ideal device.     

催化在能源转化中的作用

在一次能源转化成二次能源特别是煤制清洁燃料和化工原料的转化过程中,催化转化起重要作用.催化是解决能源问题的关键技术.介绍了化石能源、新能源和可再生能源转换过程中的催化作用以及煤制清洁燃料和化工原料的关键技术,指出催化是解决能源问题的关键技术,对煤制清洁燃料和化工原料的发展提出思考和建议.     

Silicon nanowires prepared by electron beam evaporation in ultrahigh vacuum

ABSTRACT: One-dimensional silicon nanowires (SiNWs) were prepared by electron beam evaporation in ultrahigh vacuum (UHV). The SiNWs can be grown through either vapor-liquid-solid (VLS) or oxide-assisted growth (OAG) mechanism. In VLS growth, SiNWs can be formed on Si surface, not on SiO2 surfaces. Moreover, low deposition rate is helpful for producing lateral SiNWs by VLS. But in OAG process, SiNWs can be grown on SiO2 surfaces, not on Si surfaces. This work reveals the methods of producing large-scale SiNWs in UHV.     

生物质能的转化和利用研究

随着全球能源的紧缺和化石资源使用带来的环境污染,生物质作为重要的可再生能源之一,有着广阔的前景.作者介绍了生物质及生物质能的基本概念,综述了生物质能的4种转化技术:直接燃烧技术、固化技术、液化技术和汽化技术.并对生物质能在转化和利用中存在的问题提出了相应的解决措施.     

作物秸秆能源转化技术研究进展

利用作物秸秆生产可再生能源是解决秸秆环境污染和开辟新的能量资源的重要途径之一。作物秸秆能源转化技术主要有热解气化、厌氧消化、液化、乙醇化、直接燃烧和固化等。简要介绍了我国作物秸秆的资源量及利用现状,着重对国内外作物秸秆能源转化技术的发展、研究现状及工业化应用情况进行了详细介绍。通过对各技术特点和存在问题的分析,探讨了未来发展趋势。建议加强作物秸秆液化与乙醇化技术的系统性研究以及工艺过程的开发。     

Confined conversion of CuS nanowires to CuO nanotubes by annealing-induced diffusion in nanochannels

Copper oxide (CuO) nanotubes were successfully converted from CuS nanowires embedded in anodic aluminum oxide (AAO) template by annealing-induced diffusion in a confined tube-type space. The spreading of CuO and formation of CuO layer on the nanochannel surface of AAO, and the confinement offered by AAO nanochannels play a key role in the formation of CuO nanotubes.     

Photoelectrochemical energy conversion system modeled on the photosynthetic process

Photo-excitable electrodes were prepared by incorporating magnesium chlorophyll (MgChl) or manganese chlorophyll (MnChl) into the thin layer of such liquid cyrstals as N-(p-methoxybenzylidene)-p-butylaniline (MBBA) and 4′-heptyl-4-cyanobiphenyl (HCB), being attached to the platinum surface. The MgChl—MBBA electrode gave the positive photo-induced potential shift in an acidic solution. In sharp contrast, the negative photo-induced potential shift was developed by the MnChl—HCB electrode in an alkaline solution. The involvement of a liquid crystal prominently enhanced the photo-response of the immobilized chlorophylls. The photoelectrochemical energy conversion system modeled on the photosynthetic process was assembled by employing the MgChl—MBBA and the MnChl—HCB electrodes as a cathode and an anode, respectively. The photocurrent derived from the system was concluded to result from the decomposition of water, since an evidence for the molecular oxygen evolution at the MnChl—HCB electrode was obtained. Furthermore, the incorporation of β-carotene was found to markedly enhance the stability of the MnChl—HCB electrode.     

化学工程视野下的电化学能源转换与存储

以风力/太阳能等为代表的间歇性可再生能源发电技术为能源快速发展注入了新的活力和契机。为此,发展这些电能的高效转换与存储体系至关重要,已成为当今世界范围内的重大挑战性课题之一。基于此,本文讨论和展望了化学工程视野下的电化学能源转换与存储技术的未来发展方向,为解决该领域工业化发展中的关键科学和技术问题提供了有效指导,将全面促进电化学能源转换与存储领域的快速发展。文章从化学工程的视角综述了电化学能源转换与存储技术（二次电池、超级电容器、电化学催化等）的国内外研究发展状况,指出并剖析了该体系存在的关键科学/技术问题,主要内容包括电化学能源转换与存储领域中的三传一反、系统工程、分离工程以及绿色节能新策略等。     

Diameter-dependent internal gain in ZnO micro/nanowires under electron beam irradiation

We observed a conductivity gain in intrinsic ZnO micro/nanowires at characteristic diameter scales from nanoscale to microscale by employing metal-semiconductor-metal structures with ohmic contacts under electron beam irradiation. The conductivity is enhanced under electron beam illumination and the magnitude is inversely proportional to the micro/nanowire diameter from 400 nm to 1300 nm at constant radiation intensity. We also introduced a model to simulate the diameter-dependent electric potential distribution. We attribute these observations to the variation of the effective electron carrier density upon varying diameters of ZnO micro/nanowires, as a result of field effects from the diameter-dependent population of the surface-trapped holes.     

A few-layered graphene on alumina nanofibers for electrochemical energy conversion

A few-layered graphene on the surface of highly aligned alumina nanofibers (ANFs) with an aspect ratio of 10⁷ was synthesized in a single-step catalyst-free direct chemical vapor deposition process. The product, graphenated alumina nanofibers (G-ANFs), consisting of the ceramic nanofibers surrounded by the conductive and inert few-layered graphene, is a promising material for electrochemical applications. The synthesized material has been demonstrated to be an excellent electrocatalyst support for Pt particles in fuel cells. A 1.5-fold improvement in the mass activity has been obtained for Pt/G-ANF in comparison to the commercially available Pt/C. The electrochemical stability was found to be outstanding for acidic medium electrochemistry. Their remarkable stability and unique structure opens a new avenue for the use of this material in various electrochemical energy conversion technologies.     

The role of energy and economics in water conversion

Economics has been and will be the decisive factor in water conversion. Rising energy prices will influence the water conversion market drastically in the years to come. To enable an impartial estimation of the consequences descended there-from the cost structures of the most potential water conversion alternatives are compared and the influence of energy demand, energy price, feed water salinity, operating temperature range and plant capacity on the production cost of fresh water are presented.     

Indirect charge transfer of holes via surface states in ZnO nanowires for photoelectrocatalytic applications

In this work, ZnO nanowires with high aspect ratio were obtained by fast and simple electrochemical anodization. Morphological, structural and photoelectrochemical characteristics of the synthesized ZnO nanowires were evaluated by using different techniques: field emission scanning electron microscopy, atomic force microscopy, high resolution transmission electron microscopy, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV–VIS spectroscopy, Mott-Schottky analysis and photoelectrochemical impedance spectroscopy. The synthesized ZnO nanowires presented high roughness and high crystallinity. Besides, surface defects were identified in the sample. The value of the donor density (N_D) was in the order of 10¹⁹ cm^?3 in the dark and 10²⁰ cm^?3 under illumination. In addition, the ZnO nanowires presented good photosensibility, with a photocurrent density response 85 times higher than a ZnO compact layer, and lower resistance to charge transfer. The charge transfer processes taking place at the ZnO/electrolyte interface were studied, since these processes strongly influence the photoelectrocatalytic efficiency of the material. According to the results, the charge transfer of holes in the synthesized ZnO nanowires occurs indirectly via surface states. In this regard, surface states may be an important feature for photoelectrocatalytic applications since they could provide lower onset voltages and higher anodic current densities.     

Efficient energy utilization in single purpose desalination plants

Thermodynamic analyses and case studies were carried out on hybridized systems designed to improve single purpose desalination (SPD) plants. The first system considered is a conventional SPD connected to a steam generator by a pressure reducing valve (PRV). In the second system, this is replaced by a mechanical vapour compression MVC/MED unit, and in the third system by a thermovapour compression TVC/MED unit. In the fourth system, a reverse osmosis (RO) unit replaced the PRV, thus using the supplied steam to produce more fresh water.Results of the analysis emphasize the extra water produced and the overall performance ratio increase of the plant. The included case study showed that the plant performance of the SPD was significantly improved by using any of the above systems. The extra water produced amounted to 96, 84 and 46% of the initial plant production in the second, third and fourth system respectively.     

Multi-electron transfer catalysis for energy conversion based on abundant transition metals

While noble metals such as platinum and its alloys are widely used for energy conversion catalysis in modern technology, biological systems, by controlling molecular environments and suppressing unfavorable oxidation reactions, manage to use abundant transition metals for the same purpose. To achieve this the reaction centers should not only be embedded in a chemically stable and electronically conducting matrix, which suppresses irreversible oxidation of the transition metals, but they also have to accommodate and transfer several electrons while sustaining a favorable redox potential. This is both theoretically and chemically a significant challenge but an important step towards mass application of energy catalysts in fuel cells or for water photo-electrolysis. This contribution will specifically address the oxygen electrode, both for reduction of oxygen to water and for photo-induced oxygen evolution from water and discuss experimental progress together with efforts to reach theoretical understanding. The role of non-linear synergetic interactions towards multi-electron transfer is emphasized and relevant mechanisms discussed on the basis of model catalysts.     

Balancing electron and phonon scatterings while tailoring carrier concentration in SnTe for enhancing thermoelectric performance

Balancing electron and phonon scattering is crucial for enhancing the thermoelectric (TE) performance of materials. Herein, the TE performance of Mg-alloyed SnTe was significantly enhanced by managing lattice defects. Formation of Sn vacancies in Mg-alloyed SnTe was suppressed via Sn-compensation, leading to 23% higher carrier mobility and 29% higher power factor (PF) of Sn_0.94Mg_0.09Te than those of Sn_0.88Bi_0.03Mg_0.09Te with Bi-doping. Transmission electron microscopy analysis confirmed the formation of dense dislocation arrays in Sn_0.88Bi_0.03Mg_0.09Te, resulting in an ultra-low lattice thermal conductivity (κ_lat = 0.34 W m⁻¹K⁻¹) at 823 K. A combination of Sn-compensation and Bi-doping in Sn_0.90Bi_0.03Mg_0.09Te resulted in high PF and low κ_lat, simultaneously, owing to the balanced scatterings of electron and phonon. Furthermore, carrier concentration was optimised, with a high figure of merit (ZT ∼1.3) achieved at 873 K, ∼50% higher than that obtained by applying either Sn-compensation or Bi-doping individually.