Hydrogen In Porous Materials Research Articles

Palladium clusters, free and supported on surfaces, and their applications in hydrogen storage.

Palladium is a late transition metal element in the 4d row of the periodic table. Palladium nanoparticles show efficient catalytic activity and selectivity in a number of chemical reactions. In this paper, we review the structural and electronic properties of palladium nanoclusters, both isolated and deposited on the surface of different substrates. Careful experiments and extensive calculations have been performed for small Pd clusters which provide ample information on their properties. Work on large Pd clusters is less abundant and more difficult to perform and interpret. Cluster deposition is a method to modify material surfaces for different applications, and we report the known results for the deposition of Pd clusters on the surfaces of a number of interesting substrates: carbonaceous substrates like graphene and some layered novel materials related to graphene, metal oxide substrates, silicon and silicon-related substrates and metallic alloy substrates. Emphasis is placed on revealing how the structural, electronic and magnetic properties change when the clusters are deposited on the substrate surfaces. Some examples of chemical reactions catalyzed by supported Pd clusters and nanoparticles are reported. An issue discussed in detail is the influence of Pd on the storage of hydrogen in porous materials. Experimental work shows that the amount of stored hydrogen increases when the absorbing material is doped with Pd atoms, clusters and nanoparticles, and a spillover mechanism from the metal particle to the substrate is usually accepted as the explanation. To shed light on this issue, a critical analysis based on density functional simulations of the mechanisms of hydrogen spillover in perfect and defective graphene doped with palladium clusters is presented.

Effect of nickel on hydrogen storage behaviors of carbon aerogel hybrid

Limited conventional energy resources and serious environmental calamities have motivated researchers to find new and efficient sources of energy. The considerable efforts devoted to this end include the development of bio-diesel, solar cells, coal liq-uefaction/gasification technologies, and fuel cells. Hydrogen is considered by many an ideal energy source owing to its renewable and clean energy characteristics. In addition, it mostly produces water, which is eco-friendly compared to the byproducts of many other energy sources [1-6]. To use hydrogen as an energy source, various hydrogen stor -age methods such as the use of metal hydrides, liquefied hydrogen, and adsorption of hydrogen in porous materials have been studied [7-14]. The adsorption of hydrogen in porous materials is particularly suitable for hydrogen storage, which is critical for suit -ably utilizing hydrogen energy, owing to the reversibility and stability of this method. To date, the wide ranging attempts to develop hydrogen storage mechanisms include studies on carbon materials [15-17], metal-organic frameworks, and zeolites [18-21]. Carbon materials offer many advantages for hydrogen storage, such as easy preparation, suitable surface functional groups, low mass density, thermal stability, and hydropho -bicity [22-24]. Carbon aerogels (CAs) in particular have been recognized as potential hydrogen storage materials because of their suitable structural properties, controllable mass densities, high specific surface areas, and mesopore volumes. However, it is neces -sary to modify the surfaces of carbon materials in order to reach the hydrogen storage capacities determined by the US Department of Energy (DOE).Carbon materials containing transition metals such as platinum, copper, vanadium, and nickel exhibit attractive hydrogen storage properties [10,22,25]. Nickel is particularly prom -ising since it is easily obtained on Earth, and it is inexpensive compared to other metals and enhances hydrogen storage properties. Improved hydrogen storage capacities have been obtained with nickel-plated porous carbon nanofibers owing to the spillover of hydrogen molecules onto the metal-carbon interfaces. In general, the presence of nickel particles on carbon materials has been shown to enhance the hydrogen storage capacity [3,9,19].In this work, CAs were chemically activated by KOH to produce well-developed pore structures and ultimately increase the hydrogen storage capacities. Nickel-loaded activated carbon aerogels (ACAs/Ni hybrid materials) with various nickel content were prepared. Ni particles were loaded onto ACAs to introduce hydrogen-favorable active sites onto the ACA surfaces and improve the hydrogen storage capacities.The CAs were prepared using resorcinol as the carbon precursor and formaldehyde as the initiator. Resorcinol (7.5 g) was dissolved in a solution of distilled water (75 mL) and formaldehyde (25 g). Sodium carbonate was then added to this solution, and the mixture was stirred for 3 h in an open container and dried for 3 h at room temperature. Subsequently, the wet gel was dried at 80°C for 48 h and then immersed in an acetone solution for 24 h without stirring. The aerogels were obtained after drying at 80°C for 24 h. Prior to use, the aerogels were carbonized in a furnace with a heating rate of 2°Cmin

Analysis of optimal conditions for adsorptive hydrogen storage in microporous solids

There is much current interest in the storage of hydrogen in porous materials for mobile energy applications. Despite significant hydrogen storage capacities having been observed recently for some synthesised materials, the identification of optimal operating conditions (pressure and temperature) is perhaps an even more important consideration from an engineering and applied science perspective. There will be pressure and temperature limits for effective use of an adsorptive storage system, because the adsorbent will always displace a volume in the storage container, and so at very high pressures the amount of hydrogen stored at a given temperature will be greater for a container with no adsorbent. In order for an adsorbent to be used there has to be some gain in the amount of the hydrogen stored to compensate for the cost and mass of the solid. We present a methodology by which the pressure and temperature ranges where it is advantageous to use adsorptive storage can be easily identified and the real gain of using such systems in terms of the absolute amount of hydrogen stored can be quantified. Using a well-characterised commercial activated carbon as an example system, we modelled high pressure hydrogen sorption isotherms and identified the operating conditions for which there is a significant increase in storage capacity from using an adsorbent as opposed to storage in the same volume via compression of hydrogen at the same temperature. A novel comparison of the density enhancement in the micropores with respect to the bulk hydrogen gas, as well as the influence of incorporating different amounts of adsorbent into a high pressure storage container is also presented.

On the Enhancement of Molecular Hydrogen Interactions in Nanoporous Solids for Improved Hydrogen Storage

The need for a transition toward sustainable and environmentally friendly energy sources seems to be very important nowadays. Hydrogen is being investigated as an alternative choice to fossil fuels for future transportation needs. In the past few years, significant progress has been made in storing sufficient amounts of hydrogen in porous materials. In particular, nanostructured materials can bind H2 with adequate strength required for adsorptive storage. In this Perspective, an analysis of the types of interactions between molecular hydrogen and the host material is performed, supported by illustrative examples from the literature. Guidelines for the enhancement of hydrogen interaction with the material’s pore structure and novel directions for designing materials with higher storage performance are proposed.

Metal-organic frameworks for hydrogen storage

Physisorption of hydrogen in porous materials at cryogenic conditions is a viable mechanism for hydrogen storage in mobile applications. This storage mechanism has the advantage of possessing fast kinetics, low heat of adsorption and being completely reversible. Among all porous materials, metal-organic frameworks (MOFs) are the best candidates for H 2-adsorption, since they consist of light atoms, are highly porous and their pore dimensions can be tailored by chemical engineering. Additionally, MOFs show the highest storage capacity of any other porous material. Different properties of the material, like specific surface area, composition and pore size can influence the storage capacity. Therefore, an understanding about the correlation between adsorption properties and structure of MOFs is necessary to specifically improve these materials for hydrogen storage. Our main achievements in the investigation of H 2 storage in MOFs are discussed and compared to results reported in literature.

Design Requirements for Metal-Organic Frameworks as Hydrogen Storage Materials

Storing an acceptable density of hydrogen in porous materials by physisorption at room temperature and reasonable pressures is a challenging problem. Metal-organic frameworks (MOFs) are a new class of nanoporous materials that have shown early promise for meeting this goal. They have extremely large specific surface areas, but the heats of adsorption to date are too low to provide significant storage at room temperature. In this work, molecular simulations are used to provide guidelines for the design of MOFs for hydrogen storage. To learn how much the heat of adsorption must be increased to meet current targets, we artificially increase the hydrogen/MOF Lennard-Jones attraction. The correlation of the amount of hydrogen adsorbed with the heat of adsorption, the surface area, and the free volume is revisited. We also review the distinction between excess and absolute adsorption and show that comparing the density of hydrogen within the free volume of materials provides useful insight. The simulation resul...