Metal alloys and carbon nanomaterials as potential hydrogen storage materials

Comparative analysis of metals (as well as their alloys and intermetallic compounds) and various carbon nanomaterials as working substances for hydrogen storage and transportation systems has been performed. It has been shown that, because of the fundamental difference in the nature of interaction with hydrogen of these two large classes of compounds, the fields of their application (as well as their performance) are certainly different. Some theoretical calculations and concepts concerning the hydrogen capacity of the materials under consideration have been critically surveyed.     

Enhanced hydrogen storage capacity of high surface area zeolite-like carbon materials

We report the synthesis of zeolite-like carbon materials that exhibit well-resolved powder XRD patterns and very high surface area. The zeolite-like carbons are prepared via chemical vapor deposition (CVD) at 800 or 850 degrees C using zeolite beta as solid template and acetonitrile as carbon precursor. The zeolite-like structural ordering of the carbon materials is indicated by powder XRD patterns with at least two well-resolved diffraction peaks and TEM images that reveal well-ordered micropore channels. The carbons possess surface area of up to 3200 m2/g and pore volume of up to 2.41 cm3/g. A significant proportion of the porosity in the carbons (up to 76% and 56% for surface area and pore volume, respectively) is from micropores. Both TEM and nitrogen sorption data indicate that porosity is dominated by pores of size 0.6-0.8 nm. The carbon materials exhibit enhanced (and reversible) hydrogen storage capacity, with measured uptake of up to 6.9 wt % and estimated maximum of 8.33 wt % at -196 degrees C and 20 bar. At 1 bar, hydrogen uptake capacity as high as 2.6 wt % is achieved. Isosteric heat of adsorption of 8.2 kJ/mol indicates a favorable interaction between hydrogen and the surface of the carbons. The hydrogen uptake capacity observed for the zeolite-like carbon materials is among the highest ever reported for carbon (activated carbon, mesoporous carbon, CNTs) or any other (MOFs, zeolites) porous material.     

Metal-organic frameworks—New materials for hydrogen storage

Published data on the physical sorption of hydrogen by new materials with a large specific surface area, crystalline microporous metal-organic frameworks (MOFs), are systematized and analyzed. The hydrogen-accumulating properties of MOFs are compared with those of traditional materials (charcoals and zeolites) and nanocarbon systems. The role of secondary hydrogen spillover in the development of new approaches to increase the adsorption capacity of hydrogen storage materials is separately considered.     

Theoretical realization of cluster-assembled hydrogen storage materials based on terminated carbon atomic chains

The capacity of carbon atomic chains with different terminations for hydrogen storage is studied using first-principles density functional theory calculations. Unlike the physisorption of H(2) on the H-terminated chain, we show that two Li (Na) atoms each capping one end of the odd- or even-numbered carbon chain can hold ten H(2) molecules with optimal binding energies for room temperature storage. The hybridization of the Li 2p states with the H(2)σ orbitals contributes to the H(2) adsorption. However, the binding mechanism of the H(2) molecules on Na arises only from the polarization interaction between the charged Na atom and the H(2). Interestingly, additional H(2) molecules can be bound to the carbon atoms at the chain ends due to the charge transfer between Li 2s2p (Na 3s) and C 2p states. More importantly, dimerization of these isolated metal-capped chains does not affect the hydrogen binding energy significantly. In addition, a single chain can be stabilized effectively by the C(60) fullerenes termination. With a hydrogen uptake of ～10 wt.% on Li-coated C(60)-C(n)-C(60) (n = 5, 8), the Li(12)C(60)-C(n)-Li(12)C(60) complex, keeping the number of adsorbed H(2) molecules per Li and stabilizing the dispersion of individual Li atoms, can serve as better building blocks of polymers than the (Li(12)C(60))(2) dimer. These findings suggest a new route to design cluster-assembled hydrogen storage materials based on terminated sp carbon chains.     

Thermodynamics study of hydrogen storage materials

The growing use of conventional energy such as fossil fuels results in problems degrading our environment. Hydrogen is frequently discussed as a clean energy in the future without pollution. However, efficient and safe storage of hydrogen constitute a key challenge and unresolved problem. One of the main options is solid-state storage technology. A successful solid-state reversible storage material should meet the requirements of high storage capacity, suitable thermodynamic properties, reversibility and fast adsorption and desorption kinetics. This feature article focuses mainly on the development of thermodynamic improvement of hydrogen storage materials in the past few years including the complex hydride, ammonia borane, and metal-organic frameworks.     

Electrochemical storage of hydrogen in nanocarbon materials: electrochemical characterization of carbon black matrices

In this work, various types of carbon black are electrochemically characterized to study their possible use in the electrochemical evaluation of fullerene materials as hydrogen storage candidates. The cyclic voltammetry and chronopotentiometry studies were performed in alkaline media, 6 M KOH, with carbon paste electrodes. Differences in the electrodes' electrochemical response and their correlation with the various surface chemistries, morphology and doping species of carbon blacks suggest a stronger dependency on the presence of doping agents (foreign metals) and on the surface structure than on the carbon black surface area. The study allows the selection of appropriate carbon black materials to be used as matrixes in future fullerene composite studies. Electronic Publication     

Electrospun zeolite-templated carbon composite fibres for hydrogen storage applications

Research on Chemical Intermediates - The current study explored the application of the electrospinning technique to produce multi-hierarchical composites for hydrogen storage applications....     

Solution-phase synthesis of heteroatom-substituted carbon scaffolds for hydrogen storage

This paper reports a bottom-up solution-phase process for the preparation of pristine and heteroatom (boron, phosphorus, or nitrogen)-substituted carbon scaffolds that show good surface areas and enhanced hydrogen adsorption capacities and binding energies. The synthesis method involves heating chlorine-containing small organic molecules with metallic sodium at reflux in high-boiling solvents. For heteroatom incorporation, heteroatomic electrophiles are added to the reaction mixture. Under the reaction conditions, micrometer-sized graphitic sheets assembled by 3-5 nm-sized domains of graphene nanoflakes are formed, and when they are heteroatom-substituted, the heteroatoms are uniformly distributed. The substituted carbon scaffolds enriched with heteroatoms (boron ～7.3%, phosphorus ～8.1%, and nitrogen ～28.1%) had surface areas as high as 900 m(2) g(-1) and enhanced reversible hydrogen physisorption capacities relative to pristine carbon scaffolds or common carbonaceous materials. In addition, the binding energies of the substituted carbon scaffolds, as measured by adsorption isotherms, were 8.6, 8.3, and 5.6 kJ mol(-1) for the boron-, phosphorus-, and nitrogen-enriched carbon scaffolds, respectively.     

H2 storage in carbon materials

In this work a series of commercial carbons with different structural and textural properties were characterised and evaluated for their application in hydrogen storage. The results showed that temperature has a greater influence on the storage capacity of carbons than pressure. The highest H₂ storage capacity at 298 K and 90 bar was 0.5 wt%, while at 77 K and atmospheric pressure it was 2.9 wt%. It is also showed that, in order to predict the hydrogen storage capacity of carbon material both at cryogenic and ambient temperature, the only use of BET surface area or total micropore volume obtained from N₂ adsorption isotherm may be insufficient, the characterization of the narrow microporosity is needed due to its high contribution to hydrogen adsorption capacity. The process involved in hydrogen storage in pure carbon materials seems to be physisorption. Morphological or structural characteristics have no influence, at least on gravimetric storage capacity.     

New isoreticular metal-organic framework materials for high hydrogen storage capacity

We propose new isoreticular metal-organic framework (IRMOF) materials to increase the hydrogen storage capacity at room temperature. Based on the potential-energy surface of hydrogen molecules on IRMOF linkers and the interaction energy between hydrogen molecules, we estimate the saturation value of hydrogen sorption capacity at room temperature. We discuss design criteria and propose new IRMOF materials that have high gravimetric and volumetric hydrogen storage densities. These new IRMOF materials may have gravimetric storage density up to 6.5 wt % and volumetric storage density up to 40 kg H2/m3 at room temperature.     

Microbe-derived carbon materials for electrical energy storage and conversion

Microbes are microscopic living organisms that surround us which include bacteria, archaea, most protozoa, and some fungi and algae. In recent years, microbes have been explored as novel precursors to synthesize carbon-based(nano)materials and as substrates or templates to produce carbon-containing(nano)composites. Being greener and more affordable, microbe-derived carbons(MDCs) offer good potential for energy applications. In this review, we describe the unique advantages of MDCs and outline the common procedures to prepare them. We also extensively discuss the energy applications of MDCs including their use as electrodes in supercapacitors and lithium-ion batteries, and as electrocatalysts for processes such as oxygen reduction, oxygen evolution, and hydrogen evolution reactions which are essential for fuel cell and water electrochemical splitting cells. Based on the literature trend and our group's expertise, we propose potential research directions for developing new types of MDCs. This review, therefore, provides the state-of-the-art of a new energy chemistry concept. We expect to stimulate future research on the applications of MDCs that may address energy and environmental challenges that our societies are facing.     

Experimental study on high-pressure adsorption of hydrogen on activated carbon

A systematic measurement of H2 adsorption on activated carbon over a wide scope of conditions was completed for the first time using a novel cryostat developed by the present authors. The equilibrium temperatures covered 77-298 K with the space of about 20 K, and the equilibrium pressures increased from 0 to about 7MPa. A set of adsorption/desorption isotherms was obtained by a standard volumetric method. This set of experimental data was fitted to all the well-known models of type-I isotherms, and Dubinin-Astakhov (D-A) equation was found to be the best-fit one On the basis of D-A model one can predict adsorption with relative error of ±4%. A 3-dimensional adsorption surface was also constructed, and the isosteric heat of adsorption was analytically determined. Except in the low pressure area, the calculated values agreed well with the experimental ones. Finally, the troubles encountered in applying D-A equation to supercritical adsorption is discussed.     

新型储氢材料及其热力学与动力学问题

氢能作为一种理想的二次能源受到了国内外科研工作者的广泛关注,研制可以在室温和较低压力下方便、安全、高效地储存氢能的材料是氢能发展的瓶颈.到目前为止,固态储氢材料以能量密度高及安全性好等优势被认为极具应用前景,其中以轻质元素构成的氢化物(包括硼氢化物/铝氢化物(可用通式A(MH4)n表示,其中A是碱金属(Li,Na,K)或碱土金属(Be,Mg,Ca);M是硼或铝;n=1～4)、氨基氢化物(如LiNH2等))、氨硼烷(NH3BH3)、金属有机骨架材料(MOFs)是新型储氢材料研究领域的热点,本文将着重就目前这几类储氢材料的研究当中所涉及到的一些热力学及动力学问题进行总结探讨.     

The potential of organic polymer-based hydrogen storage materials

The challenge of storing hydrogen at high volumetric and gravimetric density for automotive applications has prompted investigations into the potential of cryo-adsorption on the internal surface area of microporous organic polymers. A range of Polymers of Intrinsic Microporosity (PIMs) has been studied, the best PIM to date (a network-PIM incorporating a triptycene subunit) taking up 2.7% H(2) by mass at 10 bar/77 K. HyperCrosslinked Polymers (HCPs) also show promising performance as H(2) storage materials, particularly at pressures >10 bar. The N(2) and H(2) adsorption behaviour at 77 K of six PIMs and a HCP are compared. Surface areas based on Langmuir plots of H(2) adsorption at high pressure are shown to provide a useful guide to hydrogen capacity, but Langmuir plots based on low pressure data underestimate the potential H(2) uptake. The micropore distribution influences the form of the H(2) isotherm, a higher concentration of ultramicropores (pore size <0.7 nm) being associated with enhanced low pressure adsorption.     

Covalent organic frameworks as exceptional hydrogen storage materials

We report the H2 uptake properties of six covalent organic frameworks (COFs) from first-principles-based grand canonical Monte-Carlo simulations. The predicted H2 adsorption isotherm is in excellent agreement with the only available experimental result (3.3 vs 3.4 wt % at 50 bar and 77 K for COF-5), also reported here, validating the predictions. We predict that COF-105 and COF-108 lead to a reversible excess H2 uptake of 10.0 wt % at 77 K, making them the best known storage materials for molecular hydrogen at 77 K. We predict that the total H2 uptake for COF-108 is 18.9 wt % at 77 K. COF-102 shows the best volumetric performance, storing 40.4 g/L of H2 at 77 K. These results indicate that the COF systems are most promising candidates for practical hydrogen storage.     

纳米结构储氢材料的计算研究与设计

对B原子掺杂的石墨烯、碳纳米管和富勒烯、MB2纳米管和ca表面覆盖的纳米管体系的氢气吸附和存储性能进行了第一原理计算,结果表明在表面曲率比较大的碳材料体系中掺B可以增强其对H2的吸附作用;过渡金属原子与H2由于Kubas作用而表现出很大的H2吸附能;碱土金属Ca离子化后的带电电荷的材料体系,由于与H2发生极化作用,也会增强氢气的吸附性能．综合我们的结果和储氢材料研究的最新进展,讨论了影响储氢材料性能的相关因素,就如何增强材料与H2之间的相互作用,使H2吸附能在0．2～0．4eV之间,能够在温和的条件下吸／放氢,并且具有较大的重量和体积储氢量等问题作了简要论述,这些原理对纳米结构储氢材料的设计有一定的指导意义．     

Na-coated hexagonal B36 as superior hydrogen storage materials

Based on van der Waals corrected density functional theory, we show that Na atoms acting as decoration metals are not inclined to form clusters due to a large binding energy of 3.31 eV, indicating a promising good reversible hydrogen storage. Both the polarization mechanism and the orbital hybridizations contribute to the adsorption of hydrogen molecules (storage capacity of 4.4 wt%) with optimal adsorption energy of 0.25 eV/H₂. Additionally, the dimerization of these isolated B₃₆ does not remarkably affect the number of adsorbed H₂ per Na atom. Our results may serve as a guide in the design of new hydrogen storage materials based on low-dimension boron clusters.     

Study of borohydride ionic liquids as hydrogen storage materials

Stability of borohydrides is determined by the localization of the negative charge on the boron atom.Ionic liquids(ILs) allow to modify the stability of the borohydrides and promote new dehydrogenation pathways with a lower activation energy. The combination of borohydride and IL is very easy to realize and no expensive rare earth metals are required. The composite of the ILs with complex hydrides decreases the enthalpy and activation energy for the hydrogen desorption. The Coulomb interaction between borohydride and IL leads to a destabilization of the materials with a significantly lower enthalpy for hydrogen desorption. Here, we report a simple ion exchange reaction using various ILs, such as vinylbenzyltrimethylammonium chloride([VBTMA][Cl]), 1-butyl-3-methylimidazolium chloride([bmim][Cl]), and 1-ethyl-1-methylpyrrolidinium bromide([EMPY][Br]) with NaBH_4 to decrease the hydrogen desorption temperature. Dehydrogenation of 1-butyl-3-methylimidazolium borohydride([bmim][BH_4]) starts below 100 ℃. The quantity of desorbed hydrogen ranges between 2.4 wt% and 2.9 wt%, which is close to the theoretical content of hydrogen. The improvement in dehydrogenation is due to the strong amine cation that destabilizes borohydride by charge transfer.     

Microporous metal organic materials: promising candidates as sorbents for hydrogen storage

Advancement in hydrogen storage techniques represents one of the most important areas of today's materials research. While extensive efforts have been made to the existing techniques, there is no viable storage technology capable of meeting the DOE cost and performance targets at the present time. New materials with significantly improved hydrogen adsorption capability are needed. Microporous metal coordination materials (MMOM) are promising candidates for use as sorbents in hydrogen adsorption. These materials possess physical characteristics similar to those of single-walled carbon nanotubes (SWNTs) but also exhibit a number of improved features. Here, we report a novel MMOM structure and its room-temperature hydrogen adsorption properties.     

Solid-state thermolysis of ammonia borane and related materials for high-capacity hydrogen storage

Ammonia borane (NH(3)BH(3), AB) is a unique molecular crystal containing an intriguingly high density of hydrogen. In the past several years, AB has received extensive attention as a promising hydrogen storage medium. Several strategies have been successfully developed for promoting H(2) release and for suppressing the evolution of volatile by-products from the solid-state thermolysis of AB. Several potentially cost-effective and energy-efficient routes for regenerating AB from the spent fuels have been experimentally demonstrated. These remarkable technological advances offer a promising prospect of using AB-based materials as viable H(2) carriers for on-board application. In this perspective, the recent progresses in promoting H(2) release from the solid-state thermolysis of AB and in developing regeneration technologies are briefly reviewed.