耦合相变储热的金属氢化物反应器吸氢过程模拟

基于金属氢化物储氢反应,建立了相变材料蓄热的固体储氢反应器模型,模拟研究了吸氢压力等操作参数及相变材料的相变温度、固(液)态导热系数、相变潜热等物性参数对固体储氢反应器工作过程的影响. 结果表明,相变材料的固态导热系数和相变潜热对固体储氢反应器性能的影响较小,相变温度和液态导热系数对反应器性能影响较大. 相变温度越低,液态导热系数越大,储氢反应器性能越好. 在使用最优的相变材料储能时,提高充入氢气的压力可加快反应速率,强化相变材料的传热,有助于进一步优化反应器的储氢性能.     

大容量镁基储氢材料及其储氢性能

结合Mg-C纳米晶复合储氢材料的研究,对目前大容量镁基储氢材料研究结果进行了分析,指出用机械合金化法制备Mg纳米晶可提高其储氢密度、改善其动力学性能,但材料放氢温度一般较高。作者课题组将碳微晶与Mg复合,并引入金属催化剂,以降低MgH2分解温度。差热扫描量热分析(DSC)表明Mg-C纳米晶复合储氢材料的初始放氢温度为201~240℃,降低了60~90℃,其热力学性能得到了较大的改善。     

Tin and tin–titanium as catalyst components for reversible hydrogen storage of sodium aluminium hydride

This paper is concerned with the effects of adding tin and/or titanium dopant to sodium aluminium hydride for both dehydrogenation and re-hydrogenation reactions during their reversible storage of molecular hydrogen. Temperature programmed decomposition (TPD) measurements show that the dehydrogenation kinetics of NaAlH₄ are significantly enhanced upon doping the material with 2 mol% of tributyltin hydride, Sn(Bu)₃H but the tin catalyst dopant is shown to be inferior than titanium. On the other hand, in this preliminary work, a significant synergetic catalytic effect is clearly revealed in material co-doped with both titanium and tin catalysts which shows the highest reversible rates of dehydrogenation and re-hydrogenation (after their hydrogen depletion). The re-hydrogenation rates of depleted Sn/Ti/NaAlH₄ evaluated at both 9.5 and 140 bars hydrogen are also found to be favourable compared to the Ti/NaAlH₄, which clearly suggest the importance of the catalyst choice. Basing on these results some mechanistic insights for the catalytic reversible dehydrogenation and re-hydrogenation processes of Sn/Ti/NaAlH₄ are therefore made.     

Electric field induced ultra-high actuation in a bulk carbon nanotube structure

Electric-field induced nonlinear actuation behavior is demonstrated in a bulk nanotube (CNT) structure under ambient conditions. Completely recoverable and non-degradable actuation over several cycles of electric-field is measured in these structures. A symmetric and polarity independent displacement corresponding up to an axial strain of 14% is measured upon application of a low strength electric field of 4.2 kV/m in the axial direction. However, a much lower strain of ∼1% is measured in the radial (or, transverse) direction. Furthermore, the electric field induced actuation increases by more than a factor of 2 upon impregnating the CNT cellular structure with copper oxide nano-particles. An electrostriction mechanism, based on the electric-field induced polarization of CNT strands, is proposed to account for the reported actuation behavior.     

Electric field induced splitting of the preferred orientation in PMN-PT textured ceramics

We have performed studies of the orientation distribution in <001>_C textured, 0.03(Na_1/2Bi_1/2)TiO₃ - 0.97[0.715Pb(Mg_1/3Nb_2/3)TiO₃ - 0.285PbTiO₃] (0.03NBT-0.97[PMN-28.5PT]) ceramics by a pole figure method, comparing the results to those for PMN-PT single crystal and polycrystal samples. The pole figures about the (001) zone are found to have monoclinic, Ma, phase for textured ceramics in the annealed condition and were similar to those for electrically poled single crystals. However, electrical poling of the textured ceramics resulted in a doublet splitting of the orientation distribution about the direction that defined the original grain texturing. Studies of pole figures about other high-symmetry zones also revealed the development of some degree of preferred orientation along the in-plane directions after poling. Our findings demonstrate that E-field induced phase transformation and domain textures superimpose with that of preferred grain orientations, giving rise to a unique texture symmetry for PMN-PT. The texture symmetry changes are driven by minimization of the elastic strain energy, and have an important effect upon the piezoelectric properties.     

基于电化学性能的La-Mg-Ni系储氢合金的成分优化

以La-Mg-Ni系A2B7型储氢合金为研究对象,系统分析了合金A、B侧元素含量对其电化学性能的影响。对La1-m-n-y Pr m Nd n Mg y(Ni1-z Co z)x合金的容量和衰减速率进行了讨论。结果表明,合金容量随B/A值的增大先增大后减小,当x=3.5时,合金的容量最大,衰减速率最小;最佳的合金配比为La0.5Pr0.2Nd0.1Mg0.2(Ni0.8Co0.2)3.5。XRD分析表明,La1-m-n-y Pr m Nd n Mg y(Ni1-z Co z)x的合金主相结构均为Ce2Ni7型La2Ni7相。     

Molecular hydrogen and spiltover hydrogen storage on high surface area carbon sorbents

A series of templated carbons with various high surface areas (2033–3798 m²/g) have been prepared using various microporous zeolites as hard templates. Molecular hydrogen storage and spiltover hydrogen storage on these templated carbons were investigated and compared with superactivated carbon AX-21 and other reported porous carbon sorbents at 298 K and 100 atm. Two relationships between the surface areas of these carbons and their hydrogen capacities were obtained. The relationship between molecular hydrogen capacity and surface area showed a 0.23 wt.% H₂/1000 m²/g of carbon sorbent at 298 K and 100 atm, indicating that merely increasing surface areas of the carbon sorbents cannot achieve a significant molecular hydrogen capacity at ambient temperature. Spiltover hydrogen storage was achieved by doping Pt nanoparticles (as dissociative hydrogen source) on these carbons (spiltover hydrogen receptor). Our first result on the relationship between the spiltover hydrogen capacity and surface area showed 0.4 wt.% H₂/1000 m²/g of carbon sorbent at 298 K and 100 atm, which indicated that storage via spillover can lead to an average of 70% enhancement compared to molecular hydrogen storage.     

A light-driven reversible conductance switch based on a few-walled carbon nanotube/azobenzene hybrid linked by a flexible spacer

An azobenzene molecule (AZO) with a flexible alkyl chain was attached to the sidewall of few-walled carbon nanotube (FWCNT) to form a FWCNT-chain-AZO hybrid by covalent bonding. Transmission electron microscopy image shows individually well-dispersed FWCNT packed underneath AZO molecules. The flexible spacer between the FWCNT and the AZO led to the efficient photoisomerization and thermal reversibility of the FWCNT-chain-AZO due to an increase of free volume. A light-driven electronic switch based on two FWCNT/AZO hybrids was fabricated. Current-voltage plots showed a marked continuous increase in conductance of the FWCNT-chain-AZO switch due to efficient trans-to-cis photoisomerization. Reversible conductance of the electronic switch during multiple cycles through on/off switching of the light was obtained due to reversible conformation changes.     

有机液态氢化物可逆储放氢技术进展

有机液态氢化物可逆储放氢技术是一种具有独特优点的新型储氢技术.介绍了这种储氢技术的原理和特点,综述了国内外研究现状.指出今后应从开发高效脱氢催化剂和膜反应器两个角度出发改进该系统的脱氢效率.     

凹凸棒石黏土在储氢材料中应用探索

安全、高效、低成本的高容量储氢材料的研究尚处于攻克阶段。分析比较多孔储氢材料的研究现状,期望探索出新型多孔储氢材料。天然微纳米材料凹凸棒石黏土,表面多沟槽、内部多孔道,富含羟基、沸石水和结构水,在储氢领域具有巨大的应用价值。将其应用于新能源领域,探索其在储氢材料中应用的技术方法,开辟储氢材料一个新的方向。     

螺蛳壳和玉米芯复合吸附剂的制备及其对BP-3的去除

以废弃生物质材料螺蛳壳(SS)和玉米芯(CC)为原料,通过水浴加热法制备螺玉粉(SCC)吸附剂,考察其对2-羟基-4-甲氧基二苯甲酮(BP-3)的吸附性能。SS和CC的协同作用可以提升SCC对BP-3的吸附性能(82%),明显优于纯的SS(64%)和CC(54%)吸附BP-3的效果。当BP-3的初始浓度为50μmol/L,pH=5,吸附时间为270 min时达到吸附平衡状态。吸附过程符合准二级动力学和Langmuir等温模型,吸附属于单分子层吸附,且是一个先快速后缓慢的过程,拟合得到最大吸附容量为9.34 mg/g。     

Hydrogen storage in trimethylamine hydrate: Thermodynamic stability and hydrogen storage capacity of hydrogen+trimethylamine mixed semi-clathrate hydrate

The thermodynamic stability and hydrogen occupancy for the hydrogen+trimethylamine mixed semi-clathrate hydrate system were investigated by means of phase equilibrium (pressure–temperature) measurements and Raman spectroscopic analyses. The hydrogen molecule gradually advanced to occupy the empty small cage of trimethylamine hydrate in proportion to pressure increase. Almost all small cages were filled up with the hydrogen molecules at about 80 MPa. Isothermal Raman spectroscopic analysis showed that the absorption-rate of hydrogen to the pre-treated trimethylamine hydrate was comparable to those of tetrahydrofuran hydrate. Only one hydrogen molecule was enclosed with one small cage at the equilibrium state in pre-treated trimethylamine hydrate.     

Electric field induced phase transition and accompanying giant poling strain in lead-free NaNbO3-BaZrO3 ceramics

A series of phase transitions in (1-x)NaNbO₃-xBaZrO₃ ((1-x)NN-xBZ) ceramics was observed from antiferroelectric orthorhombic phase to ferroelectric orthorhombic phase and finally into ferroelectric rhombohedral phase with increasing x. An electric field induced irreversible phase transition was found in different compositions, irrespective of their virgin phase structures. Particularly, an antiferroelectric orthorhombic phase is irreversibly transformed into a ferroelectric monoclinic phase within 0.02?≤?x?≤?0.05, leading to a giant poling strain of ～0.58%. This is much larger than that observed in ferroelectric orthorhombic (0.06?≤?x?≤?0.07) and rhombohedral phases (0.08?≤?x?≤?0.11) suffering from an irreversible ferroelectric-ferroelectric (monoclinic) phase transition. The synchrotron x-ray diffraction and the measurement of longitudinal and transverse strains suggest that this irreversible phase transition should involve not only a distinct volume expansion, but also an obvious lattice elongation. The present study demonstrates a unique nature of the composition and field dependent phase stability and an underlying mechanism of giant poling strains in NN-BZ ceramics.     

Perspectives and challenges of hydrogen storage in solid-state hydrides

Hydrogen has been widely considered as a clean energy carrier that bridges the energy producers and energy consumers in an efficient and safe way for a sustainable society. Hydrogen can be stored in a gas, liquid and solid states and each method has its unique advantage. Though compressed hydrogen and liquefied hydrogen are mature technologies for industrial applications, appropriate measures are necessary to deal with the issues at high pressure up to around 100 MPa and low temperature at around 20 K. Distinct from those technologies, storing hydrogen in solid-state hydrides can realize a more compact and much safer approach that does not require high hydrogen pressure and cryogenic temperature. In this review, we will provide an overview of the major material groups that are capable of absorbing and desorbing hydrogen reversibly. The main features on hydrogen storage properties of each material group are summarized, together with the discussion of the key issues and the guidance of materials design, aiming at providing insights for new material development as well as industrial applications.     

Electric field phenomena in fluidized and fixed beds

Stabilization of a bed of dielectric particles against fluidization by an electric field (≥ 10³ volts/cm) is described. Glass bead and silica gel particle beds have been observed to behave as packed beds with flow rates (and pressure drops) of the fluidizing gas up to 15 times the normal incipient fluidization rate. The pressure drop at the breakup of this fixed bed was dependent on the second power of voltage, the particular bed material, and geometry of the system. Under suitable conditions 100% bed expansion without diffusive particle motion or bubble formation was obtained using silica gel particles. Comparison with iron particle bed-magnetic field effects are presented. Surface polarization charge effects are the simplest explanation of the phenomena. Several of the possible applications are suggested, such as precipitation enhancement in an aerosol filter or as a new tool for investigating aggregative fluidization.     

Recent applications of carbon nanotubes in hydrogen production and storage

Hydrogen is actually of great interest because it is the cleanest, sustainable and renewable energy carrier with a significantly reduced impact on the environment. In the future, hydrogen energy systems are expected to progressively replace the existing fossil fuels. Although hydrogen possesses significant advantages, it also exhibits major drawbacks in its utilization. The most important of them are production costs and storage characteristics. Carbon nanotubes (CNTs) have proven to possess ability as support for the fabrication of efficient heterogeneous catalysts in hydrogen production processes. Moreover, CNTs represent convenient adsorbent material that could form the basis of technologically viable hydrogen storage systems. This paper gives an overview of technologies used in the carbon nanotubes production and in the production and storage of hydrogen. In particular, it investigates the feasibility of CNTs and CNTs based catalyst materials in the mentioned processes. Our purpose is to overview the challenges of hydrogen production and storage technologies based on CNTs, to discuss and compare the different results published, and to emphasize recently developed modifications of CNTs that show potential to enhance hydrogen production and storage.     

Mono-dispersed transition metal nanoparticles on boron-substituted carbon support and applications in hydrogen storage

To prepare mono-dispersed transition metal nanoparticles on activated C supports is a long scientific challenge, due to low graphene surface energy. Few polar functional groups in activated C are only located on the plane edges, which are intrinsically difficult to prevent metal clustering, especially at elevated temperatures. This paper discusses a versatile method in preparing stable and uniform transition metal (Pt, Pd, Ti, etc.) nanoparticles (diameter ∼2 nm), using a newly-developed boron-substituted carbon (BC_x) support, containing uniform B atoms distributed in the graphene layer structure, which provides a strong specific interaction; this interaction is formed by d-electrons back-donation from transition metals to the empty p-orbital in substituted B atoms. The BC_x support shows good adsorption capacity of metal precursors in solutions, and securing the forming metal nanoparticles during thermal reduction at a high temperature (>500 °C). The resulting Pt/BC₁₂ – with only 0.7 wt.% Pt content – exhibits very high surface activities. At ambient temperature, it offers an impressive hydrogen adsorption capacity at ∼0.5 wt.% per 500 m²/g surface area, which is more than 5 times higher than the corresponding activated C material with the same surface area.     

Pd@C3N4 nanocatalyst for highly efficient hydrogen storage system based on potassium bicarbonate/formate

Formate/bicarbonate system has several desirable properties such as noncorrosive and nonirritating nature, as well as facile handling, which make it an attractive candidate for a safe, reversible hydrogen storage material. Herein, Pd nanoparticles supported on mesoporous graphitic carbon nitride (mpg‐C₃N₄) for formate‐based reversible hydrogen storage is reported. The as‐developed Pd/mpg‐C₃N₄ material was shown to be a superior catalyst for the hydrogenation of high concentrations of bicarbonate to formate under mild conditions. The effects of reaction temperature, H₂ pressure, and bicarbonate concentration on the hydrogenation of bicarbonate to formate were investigated. The catalytic performance remained steady with high activity up to six hydrogenation cycles. The interaction between mpg‐C₃N₄ and Pd nanoparticles and the concerted effects of the nitrogen species located at mpg‐C₃N₄ and bicarbonate played a synergetic role in the enhancement of the performance of the catalyst for hydrogenation. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2410–2418, 2016     

电场对竖直微槽润湿及毛细流动特性影响

竖直微槽群毛细结构广泛应用在重力热管、蒸发器等散热设备内,但受重力等因素影响易达到毛细极限。引入电场的主动强化方式来提高竖直微槽的毛细极限,并通过实验和建立数学模型研究电场对竖直微槽内液体润湿及毛细流动特性的影响。结果表明,电场可以提高竖直微槽内液体润湿高度,当电场为5.0 kV时与无电场时相比,润湿高度强化比可达到30.0%。同时,电场作用下流体在微槽道内的毛细润湿流动呈分段效应：润湿流动初期,润湿高度与时间的1/2次方呈线性关系,即h-t^1/2,润湿速率与润湿高度的倒数呈线性关系,即v-1/h;润湿流动中后期,润湿高度与时间的1/3次方呈线性关系,即h-t^1/3,润湿速率与润湿高度平方的倒数呈线性关系,即v-1/h²,且润湿速率随时间呈下降趋势。     

电场对竖直微槽润湿及毛细流动特性影响

竖直微槽群毛细结构广泛应用在重力热管、蒸发器等散热设备内,但受重力等因素影响易达到毛细极限。引入电场的主动强化方式来提高竖直微槽的毛细极限,并通过实验和建立数学模型研究电场对竖直微槽内液体润湿及毛细流动特性的影响。结果表明,电场可以提高竖直微槽内液体润湿高度,当电场为5.0 kV时与无电场时相比,润湿高度强化比可达到30.0%。同时,电场作用下流体在微槽道内的毛细润湿流动呈分段效应：润湿流动初期,润湿高度与时间的1/2次方呈线性关系,即h-t^1/2,润湿速率与润湿高度的倒数呈线性关系,即v-1/h;润湿流动中后期,润湿高度与时间的1/3次方呈线性关系,即h-t^1/3,润湿速率与润湿高度平方的倒数呈线性关系,即v-1/h²,且润湿速率随时间呈下降趋势。