Showing papers on "Hydrogen storage published in 2017"

Nanomaterials For Energy Conversion And Storage

Abstract: Nanostructured materials are advantageous in offering huge surface to volume ratios, favorable transport properties, altered physical properties, and confinement effects resulting from the nanoscale dimensions, and have been extensively studied for energy-related applications such as solar cells, catalysts, thermoelectrics, lithium ion batteries, supercapacitors, and hydrogen storage systems. This review focuses on a few select aspects regarding these topics, demonstrating that nanostructured materials benefit these applications by (1) providing a large surface area to boost the electrochemical reaction or molecular adsorption occurring at the solid–liquid or solid–gas interface, (2) generating optical effects to improve optical absorption in solar cells, and (3) giving rise to high crystallinity and/or porous structure to facilitate the electron or ion transport and electrolyte diffusion, so as to ensure the electrochemical process occurs with high efficiency. It is emphasized that, to further enhance the capability of nanostructured materials for energy conversion and storage, new mechanisms and structures are anticipated. In addition to highlighting the obvious advantages of nanostructured materials, the limitations and challenges of nanostructured materials while being used for solar cells, lithium ion batteries, supercapacitors, and hydrogen storage systems have also been addressed in this review.

Dimensional effects of nanostructured Mg/MgH2 for hydrogen storage applications: A review

Abstract: Hydrogen is regarded as an ideal fuel for vehicle applications owing to its high chemical energy. However, for on-board energy storage, fuel cell electric vehicles need compact, light, and affordable hydrogen storage system to replace the pressurized hydrogen tanks. In this regard, various materials and composites have been developed for denser and safer hydrogen storage. Among them, Mg is considered as a highly promising material to store the hydrogen in terms of gravimetric and volumetric capacity. However, because of its higher thermodynamic stability and sluggish hydrogen sorption kinetics, the sorption temperature is high and the sorption time is long, limiting for practical usage. Nanoscale material designs with various dimensionalities that have been extensively studied and used in countless research and development sectors, which can provide new strategies to tackle the limitations of Mg based hydrogen storage system. This review describes the fundamental properties, preparation, activation kinetics and thermodynamic stability of various nanostructured Mg/MgH2 materials (including bulk particles, nanofilms, nanowires and nanoparticles confined in nanoporous carbon structures and encapsulated by polymers) for feasible hydrogen storage applications, and summarizes their dimensional effects.

Metal-Nanoparticle-Catalyzed Hydrogen Generation from Formic Acid

Abstract: ConspectusTo meet the ever-increasing energy demand, the development of effective, renewable, and environmentally friendly sources of alternative energy is imperative Hydrogen (H2) is a renewable, clean energy carrier, which exhibits a threefold energy density compared to gasoline; H2 is considered one of the most promising alternative energy carriers for enabling a secure, clean energy future However, the realization of a hydrogen economy is restricted by several unresolved issues Particularly, one of the most difficult challenges is the development of a safe, efficient hydrogen storage and delivery system To this end, hydrogen storage techniques based on liquid-phase chemical hydrogen storage materials have become an attractive choiceFormic acid (FA) with a high volumetric capacity of 53 g H2/L demonstrates promise as a safe, convenient liquid hydrogen carrier However, generating H2 from FA in a controlled manner at ambient temperature is still challenging, which primarily depends on the catalyst

Hydrogen Storage Technologies for Future Energy Systems

Abstract: Future energy systems will be determined by the increasing relevance of solar and wind energy. Crude oil and gas prices are expected to increase in the long run, and penalties for CO2 emissions will become a relevant economic factor. Solar- and wind-powered electricity will become significantly cheaper, such that hydrogen produced from electrolysis will be competitively priced against hydrogen manufactured from natural gas. However, to handle the unsteadiness of system input from fluctuating energy sources, energy storage technologies that cover the full scale of power (in megawatts) and energy storage amounts (in megawatt hours) are required. Hydrogen, in particular, is a promising secondary energy vector for storing, transporting, and distributing large and very large amounts of energy at the gigawatt-hour and terawatt-hour scales. However, we also discuss energy storage at the 120–200-kWh scale, for example, for onboard hydrogen storage in fuel cell vehicles using compressed hydrogen storage. This arti...

Oxygen-rich microporous carbons with exceptional hydrogen storage capacity.

Abstract: Porous carbons have been extensively investigated for hydrogen storage but, to date, appear to have an upper limit to their storage capacity. Here, in an effort to circumvent this upper limit, we explore the potential of oxygen-rich activated carbons. We describe cellulose acetatederived carbons that combine high surface area (3800 m2 g-1) and pore volume (1.8 cm3 g-1) that arise almost entirely (> 90%) from micropores, with an oxygen-rich nature. The carbons exhibit enhanced gravimetric hydrogen uptake (8.1 wt% total, and 7.0 wt% excess) at -196 oC and 20 bar, rising to a total uptake of 8.9 wt% at 30 bar, and exceptional volumetric uptake of 44 g l-1 at 20 bar, and 48 g l-1 at 30 bar. At room temperature they store up to 0.8 wt% (excess) and 1.2 wt% (total) hydrogen at only 30 bar, and their isosteric heat of hydrogen adsorption is above 10 kJ mol-1.

Thermo-electrochemical production of compressed hydrogen from methane with near-zero energy loss

Abstract: Conventional production of hydrogen requires large industrial plants to minimize energy losses and capital costs associated with steam reforming, water–gas shift, product separation and compression. Here we present a protonic membrane reformer (PMR) that produces high-purity hydrogen from steam methane reforming in a single-stage process with near-zero energy loss. We use a BaZrO3-based proton-conducting electrolyte deposited as a dense film on a porous Ni composite electrode with dual function as a reforming catalyst. At 800 °C, we achieve full methane conversion by removing 99% of the formed hydrogen, which is simultaneously compressed electrochemically up to 50 bar. A thermally balanced operation regime is achieved by coupling several thermo-chemical processes. Modelling of a small-scale (10 kg H2 day−1) hydrogen plant reveals an overall energy efficiency of >87%. The results suggest that future declining electricity prices could make PMRs a competitive alternative for industrial-scale hydrogen plants integrating CO2 capture.

Atomically Dispersed Pt on the Surface of Ni Particles: Synthesis and Catalytic Function in Hydrogen Generation from Aqueous Ammonia–Borane

Abstract: The development of cost-effective and highly efficient catalysts is of scientific importance and practical need in the conversion and utilization of clean energy. One of the strategies fulfilling that demand is to achieve high exposure of a catalytically functional noble metal to reactants to maximize its utilization efficiency. We report herein that the single-atom alloy (SAA) made of atomically dispersed Pt on the surface of Ni particles (Pt is surrounded by Ni atoms) exhibits improved catalytic activity on the hydrolytic dehydrogenation of ammonia–borane, a promising hydrogen storage method for onboard applications. Specifically, an addition of 160 ppm of Pt leads to ca. 3-fold activity improvement in comparison to that of pristine Ni/CNT catalyst. The turnover frequency based on the isolated Pt is 12000 molH2 molPt–1 min–1, which is about 21 times the value of the best Pt-based catalyst ever reported. Our simulation results indicate that the high activity achieved stems from the synergistic effect bet...

Complex metal hydrides for hydrogen, thermal and electrochemical energy storage

Abstract: Hydrogen has a very diverse chemistry and reacts with most other elements to form compounds, which have fascinating structures, compositions and properties. Complex metal hydrides are a rapidly expanding class of materials, approaching multi-functionality, in particular within the energy storage field. This review illustrates that complex metal hydrides may store hydrogen in the solid state, act as novel battery materials, both as electrolytes and electrode materials, or store solar heat in a more efficient manner as compared to traditional heat storage materials. Furthermore, it is highlighted how complex metal hydrides may act in an integrated setup with a fuel cell. This review focuses on the unique properties of light element complex metal hydrides mainly based on boron, nitrogen and aluminum, e.g., metal borohydrides and metal alanates. Our hope is that this review can provide new inspiration to solve the great challenge of our time: efficient conversion and large-scale storage of renewable energy.

Topologically Guided, Automated Construction of Metal–Organic Frameworks and Their Evaluation for Energy-Related Applications

Abstract: Metal–organic frameworks (MOFs) are promising materials for a range of energy and environmental applications. Here we describe in detail a computational algorithm and code to generate MOFs based on edge-transitive topological nets for subsequent evaluation via molecular simulation. This algorithm has been previously used by us to construct and evaluate 13 512 MOFs of 41 different topologies for cryo-adsorbed hydrogen storage. Grand canonical Monte Carlo simulations are used here to evaluate the 13 512 structures for the storage of gaseous fuels such as hydrogen and methane and nondistillative separation of xenon/krypton mixtures at various operating conditions. MOF performance for both gaseous fuel storage and xenon/krypton separation is influenced by topology. Simulation data suggest that gaseous fuel storage performance is topology-dependent due to MOF properties such as void fraction and surface area combining differently in different topologies, whereas xenon/krypton separation performance is topology...

Materials Genome in Action: Identifying the Performance Limits of Physical Hydrogen Storage

Abstract: The Materials Genome is in action: the molecular codes for millions of materials have been sequenced, predictive models have been developed, and now the challenge of hydrogen storage is targeted. Renewably generated hydrogen is an attractive transportation fuel with zero carbon emissions, but its storage remains a significant challenge. Nanoporous adsorbents have shown promising physical adsorption of hydrogen approaching targeted capacities, but the scope of studies has remained limited. Here the Nanoporous Materials Genome, containing over 850 000 materials, is analyzed with a variety of computational tools to explore the limits of hydrogen storage. Optimal features that maximize net capacity at room temperature include pore sizes of around 6 A and void fractions of 0.1, while at cryogenic temperatures pore sizes of 10 A and void fractions of 0.5 are optimal. Our top candidates are found to be commercially attractive as “cryo-adsorbents”, with promising storage capacities at 77 K and 100 bar with 30% en...

Carbon dioxide hydrogenation catalysed by well-defined Mn(i) PNP pincer hydride complexes.

Abstract: The catalytic reduction of carbon dioxide is of great interest for its potential as a hydrogen storage method and to use carbon dioxide as C-1 feedstock. In an effort to replace expensive noble metal-based catalysts with efficient and cheap earth-abundant counterparts, we report the first example of Mn(i)-catalysed hydrogenation of CO2 to HCOOH. The hydride Mn(i) catalyst [Mn(PNPNH-iPr)(H)(CO)2] showed higher stability and activity than its Fe(ii) analogue. TONs up to 10 000 and quantitative yields were obtained after 24 h using DBU as the base at 80 °C and 80 bar total pressure. At catalyst loadings as low as 0.002 mol%, TONs greater than 30 000 could be achieved in the presence of LiOTf as the co-catalyst, which are among the highest activities reported for base-metal catalysed CO2 hydrogenations to date.

Development of vanadium based hydrogen storage material: A review

Abstract: The metallic vanadium has an excellent hydrogen storage properties in comparison to other hydride forming metals such as titanium, uranium, and zirconium. The gravimetric storage capacity of vanadium is over 4 wt% which is even better than AB2 and AB5 alloys. The metallic vanadium has shown high hydrogen solubility and diffusivity at nominal temperature and pressure conditions. Consequently, vanadium is under consideration for the cost-effective hydrogen permeation membrane to replace palladium. The issues with vanadium are poor reversibility and pulverization. The poor reversibility is because of high thermal stability of β (VH/V2H) phase which eventually restricts the cyclic hydrogen storage capacity up to 2 wt% at room temperature. The pulverization is because of large crystal misfit between the metal and metal hydride phase. The hydrogen solubility, phase stability, hydrogenation-dehydrogenation kinetics, and pulverization are highly influenced by the presence of an alloying element. Therefore, worldwide efforts are to explore and optimize the alloying element which could enhance the hydrogen solubility, destabilized the β phase, improved the hydrogenation-dehydrogenation kinetics, and prevent the pulverization. The current review is a systematic presentation of these efforts to resolve the issues of vanadium as a base material for hydrogen storage and permeation membrane.

Metal Hydride Nanoparticles with Ultrahigh Structural Stability and Hydrogen Storage Activity Derived from Microencapsulated Nanoconfinement.

Abstract: Metal hydrides (MHs) have recently been designed for hydrogen sensors, switchable mirrors, rechargeable batteries, and other energy-storage and conversion-related applications. The demands of MHs, particular fast hydrogen absorption/desorption kinetics, have brought their sizes to nanoscale. However, the nanostructured MHs generally suffer from surface passivation and low aggregation-resisting structural stability upon absorption/desorption. This study reports a novel strategy named microencapsulated nanoconfinement to realize local synthesis of nano-MHs, which possess ultrahigh structural stability and superior desorption kinetics. Monodispersed Mg2 NiH4 single crystal nanoparticles (NPs) are in situ encapsulated on the surface of graphene sheets (GS) through facile gas-solid reactions. This well-defined MgO coating layer with a thickness of ≈3 nm efficiently separates the NPs from each other to prevent aggregation during hydrogen absorption/desorption cycles, leading to excellent thermal and mechanical stability. More interestingly, the MgO layer shows superior gas-selective permeability to prevent further oxidation of Mg2 NiH4 meanwhile accessible for hydrogen absorption/desorption. As a result, an extremely low activation energy (31.2 kJ mol-1 ) for the dehydrogenation reaction is achieved. This study provides alternative insights into designing nanosized MHs with both excellent hydrogen storage activity and thermal/mechanical stability exempting surface modification by agents.

Formation and Characterization of Hydrogen Boride Sheets Derived from MgB2 by Cation Exchange.

Abstract: Two-dimensional (2D) materials are promising for applications in a wide range of fields because of their unique properties. Hydrogen boride sheets, a new 2D material recently predicted from theory, exhibit intriguing electronic and mechanical properties as well as hydrogen storage capacity. Here, we report the experimental realization of 2D hydrogen boride sheets with an empirical formula of H1B1, produced by exfoliation and complete ion-exchange between protons and magnesium cations in magnesium diboride (MgB2) with an average yield of 42.3% at room temperature. The sheets feature an sp2-bonded boron planar structure without any long-range order. A hexagonal boron network with bridge hydrogens is suggested as the possible local structure, where the absence of long-range order was ascribed to the presence of three different anisotropic domains originating from the 2-fold symmetry of the hydrogen positions against the 6-fold symmetry of the boron networks, based on X-ray diffraction, X-ray atomic pair dist...

Selective Formic Acid Dehydrogenation on Pt-Cu Single-Atom Alloys

Abstract: Formic acid is a potential hydrogen storage molecule which dehydrogenates to form CO2 and H2 on metal surfaces. However, it can also decompose via a competing dehydration reaction that forms CO and H2O, reducing the amount of H2 produced and poisoning the catalyst with CO. Formic acid re-formation to hydrogen is typically performed by Pt and Pd catalysts, which while highly active for dehydrogenation also catalyze dehydration. Cu is typically not utilized, as it requires prohibitively high temperatures, although Cu surfaces are very selective toward dehydrogenation. We studied the reaction of formic acid on single-atom alloys (SAAs), consisting of single Pt atoms substituted into a Cu lattice. Surface science studies allowed us to relate alloy structure to reactivity and selectivity and visualize reaction intermediates. These experiments revealed that SAAs are able to selectively dehydrogenate formic acid with a 6-fold increase in yield in comparison to Cu. This increase in conversion is due to a more fac...