含金金属纳米颗粒用于液相化学氢化物催化制氢

液相化学氢化物以化学键的形式储存氢能,被认为是一类很有前景的化学储氢材料。液相化学氢化物的大规模应用很大程度上依赖于高效催化系统的开发。含金金属纳米颗粒在用于液相化学氢化物催化制氢中表现出优异的催化性能。本文综述了金纳米颗粒和含金异金属纳米颗粒用于液相氢化物催化制氢的最新研究进展。     

Electrochemical behavior of metal hydrides

Metal hydride electrodes are of particular interest owing to their potential and practical application in batteries. A large number of hydrogen storage materials has been characterized so far. This paper deals with the effect of the chemical nature and stoichiometry of specific alloy families (AB₅, A₂B, AB/AB₂ and AB₂) on the hydride stability, hydrogen storage capacity and kinetics of hydrogen sorption-desorption in the solid phase/gas and solid phase/electrolyte solution systems. Special attention has been paid towards the electrochemical properties of metal hydrides in terms of their performance in Ni-MH rechargeable alkaline cells. Electronic Publication     

A high-temperature,high-pressure microbalance for the determination of the hydrogen sorption characteristics of metal hydrides

The use of hydrogen as a future complementary energy vector is essentially linked to the problem of its storage and transport. Apart from conventional techniques, the storage of hydrogen in metal hydrides is considered of interest for a number of applications. To make a metal hydride a suitable hydrogen storage material, it must exhibit certain characteristics concerning in particular: (i) the hydrogen storage capacity, (ii) the dissociation pressure—temperature relationship, (iii) the heat of reaction, and (iv) the kinetics of hydrogen absorption/desorption. All these data can be determined using a microbalance capable of operating at high temperatures and pressures.The principal item of the thermogravimetric installation developed at Battelle-Geneva consists of a Sartorius balance type 4406 equipped with a heatable autoclave. The attached pressure and temperature control systems allow measurements under conditions of constant pressure (10^?5 Torr to 60 bar) and temperature (15 to 600°C), as well as the execution of pressure and temperature cycling programs at various scanning speeds.The performance and versatility of the instrument is illustrated by measuring various hydrogen sorption characteristics of the known magnesium nickel hydride and iron titanium hydride.     

Active MgH2?Mg Systems for Reversible Chemical Energy Storage

An overview of the importance of and methods available for heat storage in the form of sensible and latent heat is followed by a discussion of the advantages and disadvantages of reversible thermochemical energy storage compared to conventional energy sources such as fuels, i.e. irreversible chemical energy carriers. Of the reversible metal-hydride–metal systems, the MgH₂? Mg system is particularly attractive as a hydrogen and a high-temperature heat storage material because of its high hydrogen content and the high energy content of the Mg–H bond. The advances made in this area over the past few years, namely in catalytic hydrogenation and the doping of magnesium powders, have led to the development of “active MgH₂? Mg systems” for energy storage. The first experimental results on high-temperature heat storage (also with cooling) by coupling a MgH₂? Mg storage system with a low-temperature metal hydride storage system are presented.     

First-principle investigation of XSrH3 (X = K and Rb) perovskite-type hydrides for hydrogen storage

Hydrogen can be utilized as an energy source; therefore, hydrogen storage has received the most appealing examination interest in recent years. The investigations of hydrogen storage applications center fundamentally around the examination of hydrogen capacity abilities of recently presented compounds. XSrH₃ (X = K and Rb) compounds have been examined by density functional theory (DFT) calculations to uncover their different characteristics, as well as hydrogen capacity properties, for the first time. Studied compounds are optimized in the cubic phase, and optimized lattice constants are obtained as 4.77 and 4.99 Å for KSrH₃ and RbSrH₃, respectively. These hydrides have shown negative values of formation enthalpies as they are stable thermodynamically. XSrH₃ might be used in hydrogen storage applications because of high gravimetric hydrogen storage densities, which are 2.33 and 1.71 wt% for KSrH₃ and RbSrH₃, respectively. Moreover, electronic properties confirm the semiconductor nature of these compounds having indirect band gaps of values 1.41 and 1.23 eV for KSrH₃ and RbSrH₃, respectively. In addition, mechanical properties from elastic constants such as Young modulus and Pugh's ratio, also have been investigated, and these compounds were found to satisfy born stability conditions. Furthermore, Pugh's ratio and Cauchy pressure show that these hydrides have a brittle nature. Furthermore, thermodynamic properties such as entropy and Debye temperature have been examined using the quasiharmonic Debye model for different temperatures and pressures.     

A dehydrogenation mechanism of metal hydrides based on interactions between Hdelta+ and H-

This paper describes a reaction mechanism that explains the dehydrogenation reactions of alkali and alkaline-earth metal hydrides. These light metal hydrides, e.g., lithium-based compounds such as LiH, LiAlH4, and LiNH2, are the focus of intense research recently as the most promising candidate materials for on-board hydrogen storage applications. Although several interesting and promising reactions and materials have been reported, most of these reported reactions and materials have been discovered by empirical means because of a general lack of understanding of any underlying principles. This paper describes an understanding of the dehydrogenation reactions on the basis of the interaction between negatively charged hydrogen (H-, electron donor) and positively charged hydrogen (Hdelta+, electron acceptor) and experimental evidence that captures and explains many observations that have been reported to date. This reaction mechanism can be used as a guidance for screening new material systems for hydrogen storage.     

Problem of hydrogen storage and prospective uses of hydrides for hydrogen accumulation

Merits and demerits of existing methods of hydrogen storage are discussed. Special attention is given a metal hydride technology based on the ability of metals, intermetallic compounds, and alloys for reversible reaction with hydrogen. It is noted that the basic advantages of metal hydrides are a high volumetric hydrogen content, operational safety, technological flexibility, and low power inputs on hydrogen absorption and desorption.     

Chemical and Physical Solutions for Hydrogen Storage

Hydrogen is a promising energy carrier in future energy systems. However, storage of hydrogen is a substantial challenge, especially for applications in vehicles with fuel cells that use proton‐exchange membranes (PEMs). Different methods for hydrogen storage are discussed, including high‐pressure and cryogenic‐liquid storage, adsorptive storage on high‐surface‐area adsorbents, chemical storage in metal hydrides and complex hydrides, and storage in boranes. For the latter chemical solutions, reversible options and hydrolytic release of hydrogen with off‐board regeneration are both possible. Reforming of liquid hydrogen‐containing compounds is also a possible means of hydrogen generation. The advantages and disadvantages of the different systems are compared.     

Infrared spectra of group 14 hydrides in solid hydrogen: experimental observation of PbH4, Pb2H2, and Pb2H4

Laser-ablated Si, Ge, Sn, and Pb atoms have been co-deposited with pure hydrogen at 3.5 K to form the group 14 hydrides. The initial SiH(2) product reacts completely to SiH(4), whereas substantial proportions of GeH(2), SnH(2), and PbH(2) are trapped in solid hydrogen. Further hydrogen atom reactions form the trihydride radicals and tetrahydrides of Ge, Sn, and Pb. The observation of PbH(4) at 1815 cm(-)(1) and PbD(4) at 1302 cm(-)(1) is in agreement with the prediction of quantum chemical calculations for these unstable tetrahydride analogues of methane. In addition, new absorptions are observed for Pb(2)H(2) and Pb(2)H(4), which have dibridged structures based on quantum chemical calculations.     

Storage of hydrogen at 303 K in graphite slitlike pores from grand canonical Monte Carlo simulation

Grand canonical Monte Carlo (GCMC) simulations were used for the modeling of the hydrogen adsorption in idealized graphite slitlike pores. In all simulations, quantum effects were included through the Feynman and Hibbs second-order effective potential. The simulated surface excess isotherms of hydrogen were used for the determination of the total hydrogen storage, density of hydrogen in graphite slitlike pores, distribution of pore sizes and volumes, enthalpy of adsorption per mole, total surface area, total pore volume, and average pore size of pitch-based activated carbon fibers. Combining experimental results with simulations reveals that the density of hydrogen in graphite slitlike pores at 303 K does not exceed 0.014 g/cm(3), that is, 21% of the liquid-hydrogen density at the triple point. The optimal pore size for the storage of hydrogen at 303 K in the considered pore geometry depends on the pressure of storage. For lower storage pressures, p < 30MPa, the optimal pore width is equal to a 2.2 collision diameter of hydrogen (i.e., 0.65 nm), whereas, for p congruent with 50MPa, the pore width is equal to an approximately 7.2 collision diameter of hydrogen (i.e., 2.13 nm). For the wider pores, that is, the pore width exceeds a 7.2 collision diameter of hydrogen, the surface excess of hydrogen adsorption is constant. The importance of quantum effects is recognized in narrow graphite slitlike pores in the whole range of the hydrogen pressure as well as in wider ones at high pressures of bulk hydrogen. The enthalpies of adsorption per mole for the considered carbonaceous materials are practically constant with hydrogen loading and vary within the narrow range q(st) congruent with 7.28-7.85 kJ/mol. Our systematic study of hydrogen adsorption at 303 K in graphite slitlike pores gives deep insight into the timely problem of hydrogen storage as the most promising source of clean energy. The calculated maximum storage of hydrogen is equal to approximately 1.4 wt %, which is far from the United States Department of Energy (DOE) target (i.e., 6.5 wt %), thus concluding that the total storage amount of hydrogen obtained at 303 K in graphite slitlike pores of carbon fibers is not sufficient yet.     

多壁碳纳米管的改性及其储氢性能研究

考察了空气处理、混酸处理、H₂O₂处理和等离子体活化等化学改性和多种活性金属修饰对碳纳米管储氢性能的影响,采用TPD-H₂评价装置测试了不同样品吸附的氢气在程序升温后的脱附情况,用峰面积和氢气的校正因子计算出样品吸附氢气的体积,从而计算出碳纳米管的储氢容量.实验结果表明,化学改性和金属修饰均能明显提高碳纳米管的储氢性能,其中经过混合酸和H₂O₂化学处理并负载质量分数为20%Ni的碳纳米管,在常温常压下的氢气储存的质量分数达到2.55%,比未做任何处理的碳纳米管的储氢容量提高了7倍.     

Europium palladium hydrides

The first fully structurally characterized ternary europium palladium hydrides (deuterides) are reported. The most Eu rich compound is Eu(2)PdD(4). Its beta-K(2)SO(4) type structure (space group Pnma, a = 749.47(1) pm, b = 543.34(1) pm, c = 947.91(1) pm, Z = 4) contains tetrahedral 18-electron [PdD(4)](4)(-) complex anions and divalent Eu cations. The compound is presumably nonmetallic and shows paramagnetic behavior (mu(eff) = 8.0(2) mu(B)) with ferromagnetic ordering at T(C) = 15.1(4) K. A metallic compound at intermediate Eu content is EuPdD(3). It crystallizes with the cubic perovskite structure (space group Pm3m, a = 380.01(2) pm, Z = 1) in which palladium is octahedrally surrounded by fully occupied deuterium sites. Metallic hydrides at low Eu content form by reversible hydrogen absorption of intermetallic EuPd(2) (Fd3m, a = 775.91(1) pm, Z = 8). Depending on the experimental conditions at least three phases with distinctly different hydrogen contents x exist: EuPd(2)H(x) ( approximately )(0.1) (a = 777.02(2) pm, Z = 8, T = 298 K, p(H(2)) = 590 kPa), EuPd(2)H(x) ( approximately )(1.5) (a = 794.47(5) pm, Z = 8, T = 298 K, p(H(2)) = 590 kPa), and EuPd(2)H(x) ( approximately )(2.1) (a = 802.1(1) pm, Z = 8, T = 350 K, p(H(2)) = 610 kPa). All crystallize with cubic Laves phase derivative structures and have presumably disordered hydrogen distributions.     

Theory of surface segregation in transition metal alloys and hydrides

The surface segregation of one component in binary transition metal alloys and the surface segregation of one hydrogen isotope in transition metal hydrides containing a mixture of hydrogen isotopes are discussed in the scope of the same thermodynamic model. The binary alloys are assumed to form a disordered substitutional alloy and the random distribution of hydrogen isotopes is assumed in the case of transition metal hydrides.     

含Co或Ni的双金属及三金属纳米颗粒制备方法及其催化制氢性能

常见的氢气储存方法有液态储氢、高压气态储氢、有机化合物储氢、金属氢化物储氢、吸附储氢及液相化学储氢材料储氢等,其中液相化学储氢材料由于具有含氢量高、且可按时即需释放氢气的优点,引起了研究人员的广泛关注;选择合适的催化剂催化液相储氢材料制氢已成为一个研究热点。含有Co或Ni的双金属或三金属纳米颗粒是一种极具应用前景的催化剂,具有价格低廉、储量丰富和催化性能优异等众多优点。本文综述了含Co或Ni的双金属或三金属纳米颗粒的制备方法及其催化制氢性能,并提出了其目前研究中存在的问题和未来潜在的发展方向。     

Determination of hydrogen in oxygen containing zirconium hydrides by the hydrogen evolution method

Summary Hydrogen absorbed by pure zirconium can be determined quantitatively with a precision of better than ±1.4 mg or 16 ml per g of the sample, if the latter is dissolved in HP solution, the volume of hydrogen measured, and eq. 5 with R=0 is applied. For hydrogen and oxygen containing solid solutions the residue (ZrO₂) left after dissolution has to be collected, weighed, and the full eq. 5 has to be used. The precision of such determinations is about ±16 ml hydrogen per g of the alloy. Oxygen containing samples, if the hydrogen is absorbed at elevated temperatures, always leave the oxygen in the form of ZrO₂ which is insoluble in dilute HF solution. However, if hydrogen diffuses into oxygen containing Zr at low temperatures (e.g. room) then it may happen that ZrO₂ of smaller grain size (especially in the -solid solution region) will dissolve completely in the acid and if so, applying eq. 5, will result in too small an amount of absorbed hydrogen. This is a definite limitation of the method.This investigation was supported by the U.S. Atomic Energy Commission [AT (11-1)-73, Project 5].     

A single-component liquid-phase hydrogen storage material

The current state-of-the-art for hydrogen storage is compressed H(2) at 700 bar. The development of a liquid-phase hydrogen storage material has the potential to take advantage of the existing liquid-based distribution infrastructure. We describe a liquid-phase hydrogen storage material that is a liquid under ambient conditions (i.e., at 20 °C and 1 atm pressure), air- and moisture-stable, and recyclable; releases H(2) controllably and cleanly at temperatures below or at the proton exchange membrane fuel cell waste-heat temperature of 80 °C; utilizes catalysts that are cheap and abundant for H(2) desorption; features reasonable gravimetric and volumetric storage capacity; and does not undergo a phase change upon H(2) desorption.     

Strategies for hydrogen storage in metal--organic frameworks

Increased attention is being focused on metal-organic frameworks as candidates for hydrogen storage materials. This is a result of their many favorable attributes, such as high porosity, reproducible and facile syntheses, amenability to scale-up, and chemical modification for targeting desired properties. A discussion of several strategies aimed at improving hydrogen uptake in these materials is presented. These strategies include the optimization of pore size and adsorption energy by linker modification, impregnation, catenation, and the inclusion of open metal sites and lighter metals.