Nanomaterials for Solid State Hydrogen Storage Fuel Cells and Hydrogen Energy Series Editor: Narottam P Bansal NASA Glenn Research Center Cleveland, OH 44135 narottam.p.bansal@nasa.gov Aims and Scope of the Series During the last couple of decades, notable developments have taken place in the science and technology of fuel cells and hydrogen energy Most of the knowledge developed in this field is contained in individual journal articles, conference proceedings, research reports, etc Our goal in developing this series is to organize this information and make it easily available to scientists, engineers, technologists, designers, technical managers and graduate students The book series is focused to ensure that those who are interested in this subject can find the information quickly and easily without having to search through the whole literature The series includes all aspects of the materials, science, engineering, manufacturing, modeling, and applications Fuel reforming and processing; sensors for hydrogen, hydrocarbons and other gases will also be covered within the scope of this series A number of volumes edited/authored by internationally respected researchers from various countries are planned for publication during the next few years Titles in this series Nanomaterials for Solid State Hydrogen Storage R.A Varin, T Czujko, and Z S Wronski ISBN 978-0-387-77711-5, 2009 Modeling Solid Oxide Fuel Cells: Methods, Procedures and Techniques R Bove and S Ubertini, eds ISBN 978-1-4020-6994-9, 2008 Robert A.Varin • Tomasz Czujko Zbigniew S Wronski Nanomaterials for Solid State Hydrogen Storage Robert A Varin University of Waterloo Department of Mechanical and Mechatronics Engineering 200 University Ave W Waterloo, Ontario Canada N2L 3G1 Tomasz Czujko University of Waterloo Department of Mechanical and Mechatronics Engineering 200 University Ave W Waterloo, Ontario Canada N2L 3G1 Zbigniew S Wronski CANMET Energy Technology Centre Hydrogen Fuel Cells and Transportation Energy Natural Resources Canada Haanel Drive Ottawa, Ontario Canada K1A 1M1 ISBN: 978-0-387-77711-5 e-ISBN: 978-0-387-77712-2 DOI: 10.1007/978-0-387-77712-2 Library of Congress Control Number: 2008929618 © Springer Science+Business Media, LLC 2009 All rights reserved This work may not be translated or copied in whole or in part without the written permission of the publisher (Springer Science+Business Media, LLC, 233 Spring Street, New York, NY 10013, USA), except for brief excerpts in connection with reviews or scholarly analysis Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden The use in this publication of trade names, trademarks, service marks, and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights Printed on acid-free paper springer.com Preface Although hydrogen as a chemical element has been known to the humankind and used in various capacities for a very long time, only in the past 15 years its importance to the world population as an energy vector has gradually emerged A long-term reliance of humanity on the energy derived solely from fossil fuels, such as coal in the nineteenth and crude oil and natural gas in the twentieth century, has led to a number of new challenges facing all of us in the twenty-first century, such as sharp reduction in the world crude oil and eventually coal supply, global warming and following climate changes due to the release of growing amounts of greenhouse gas CO2, and poor urban air quality Hydrogen is essentially the only viable remedy for the growing world energy problems Hydrogen is a very attractive alternative energy vector for replacing fossil fuel-based economy The future Hydrogen Economy offers a potential solution to satisfying the global energy requirements while reducing (and eventually eliminating) carbon dioxide and other greenhouse gas emissions and improving energy security Hydrogen is ubiquitous, clean, efficient, and can be produced directly from sunlight and water by biological organisms and using semiconductor-based systems similar to photovoltaics Hydrogen can also be produced indirectly via thermal processing of biomass or fossil fuels where the development of advanced technological processes combined with a CO2 sequestration is emerging However, this rosy picture, as it usually happens in a real life, is marred by a number of obstacles which must be overcome before the Hydrogen Economy becomes a reality One of these obstacles is safe and efficient storage of hydrogen particularly for mobile/automotive applications where hydrogen gas will be supplied to fuel cells that, in turn, will power the transport vehicles in a clean, inexpensive, safe, and efficient manner From all possible solutions to hydrogen storage the one which relies upon storage in solid media (hydrides) is the most attractive one The fast emerging nanoscience/nanotechnology will allow fabricating nanomaterials for solid-state hydrogen storage that can, in a long run, revolutionize hydrogen storage This book is our modest contribution to this innovative area of hydrogen storage Wherever possible we tried to illustrate the hydrogen storage behavior by our own results In Chap 1, we introduce the reader to the motivation for the transformation to the Hydrogen Economy In a number of following sections/subsections, we v vi Preface provide a comprehensive synchronic history of development of hydrides and nanomaterials including the existing fabrication methods with a special emphasis on ball (mechanical) milling in high-energy mills Important hydride properties and experimental techniques for assessing hydrogen storage behavior are also discussed In Chap 2, we review hydrogen storage properties of selected simple metal and intermetallic hydrides with the most emphasis on magnesium hydride (MgH2) which now can be treated as a model hydride whose hydrogen storage properties in nanostructured form can be used as a benchmark for comparing the properties of other hydrides Chapter brings a thorough review of the properties of complex hydrides whose high volumetric and gravimetric capacities make them most attractive for the vehicular solid-state hydrogen storage in transportation Chapter provides information on carbons and nanocarbons as alternative means of hydrogen storage to solid hydrides This includes diamond and nanodiamond, graphene, ordered graphites and nanographites, disordered and active carbons, fullerenes, carbon nanotubes, and other nanoshapes Chapter is a sort of an executive summary where we provide a critical assessment of the present state of knowledge and make predictions for the future developments Waterloo, ON Waterloo, ON Ottawa, ON Robert A Varin Tomasz Czujko Zbigniew S Wronski Contents Introduction 1.1 1.2 Motivation: The Hydrogen Economy Brief, Synchronic History of Development of Hydrides and Nanomaterials 1.2.1 Early Investigations of Metal–Hydrogen Systems and Hydrides 1.2.2 Early Routes to Nanomaterials 1.2.3 Historical Development of Classical Hydrogen Storage AB5 Alloys 1.2.4 Historical Development of Interstitial Hydrides in Other Intermetallic Systems 1.2.5 Historical Development of Nanophase AB2 Intermetallic Hydrides 1.2.6 New Routes to Nanomaterials: Mechanical Alloying and Mechanochemical Activation 1.2.7 Historical Development of Lightweight Metal Hydrides and Hydride Complexes 1.2.8 Early Studies of Noninterstitial Transition Metal Ternary Hydrides 1.2.9 Toward Chemical/Complex Hydrides 1.2.10 Historical Development of Nanocarbons and Carbon Nanotubes 1.2.11 New Materials and Techniques 1.3 Nanoprocessing in Solid State in High-Energy Ball Mills 1.3.1 Processes for the Synthesis of Nanostructured Materials 1.3.2 Milling Processes and Equipment 1.3.3 Nanoprocessing Methods and Mechanisms 1.3.3.1 Mechanical Milling 1.3.3.2 Mechanical Alloying 7 10 13 15 16 17 18 20 21 23 25 27 27 28 37 38 39 vii viii Contents 1.3.3.3 1.3.3.4 Mechanochemical Activation Mechanochemical Synthesis (Mechanosynthesis) of Nanohydrides 1.3.3.5 Mechanical Amorphization 1.4 Important Hydride Properties and Experimental Techniques 1.4.1 Thermodynamics 1.4.1.1 Pressure–Composition–Temperature (PCT) Properties 1.4.1.2 Calculation of Activation Energy 1.4.2 PCT and Kinetic Curves Determination by Volumetric Method in a Sieverts-Type Apparatus 1.4.3 Microstructural Characterization of Ball-Milled Hydrides 1.4.4 Weight Percent of a Hydride Phase and Hydrogen by DSC Method References 40 52 55 56 56 56 60 65 71 73 74 Simple Metal and Intermetallic Hydrides 83 2.1 83 83 Mg/MgH2 2.1.1 Crystallographic and Material Characteristics 2.1.2 Hydrogen Storage Characteristics of Commercial Mg and MgH2 2.1.2.1 Absorption 2.1.2.2 Desorption 2.1.3 Hydrogen Storage Characteristics of Mechanically (Ball) Milled MgH2 2.1.3.1 Microstructural Evolution During Milling and Subsequent Cycling of Commercial MgH2 Powders 2.1.3.2 Hydrogen Absorption of Ball-milled Commercial MgH2 Powders 2.1.3.3 Hydrogen Desorption of Ball-milled Commercial MgH2 Powders 2.1.4 Hydrogen Storage Characteristics of MgH2 Synthesized by Reactive Mechanical (Ball) Milling of Mg 2.1.5 Aging Effects in Stored MgH2 Powders 2.1.6 Other Methods of Synthesis of Nanostructured MgH2 than Ball Milling 2.2 MgH2 with Catalytic Additives 2.2.1 Mg/MgH2–Metals and Intermetallics 2.2.1.1 Desorption in Vacuum 2.2.1.2 Desorption at Atmospheric Pressure of Hydrogen 2.2.2 Mg/MgH2–Metal Oxides 2.2.3 Mg/MgH2–Carbon / Graphite and Carbon Nanotubes 87 87 93 102 103 112 115 129 146 147 151 152 152 153 165 169 Contents ix 2.3 Other Metal Hydrides Containing Mg 2.4 AlH3 2.5 Other Metal and Intermetallic-based Hydrides: New Developments 2.5.1 Metal Hydrides 2.5.2 Rare-Earth AB5 Compounds 2.5.3 Titanium–Iron AB Compounds 2.5.4 Titanium and Zirconium AB2 Compounds 2.5.5 Other Novel Intermetallic Hydrides References 195 Ternary Transition Metal Complex Hydrides 3.1.1 Mg2NiH4 3.1.2 Mg2FeH6 3.1.3 Mg2CoH5 3.2 Alanates 3.2.1 NaAlH4 3.2.2 LiAlH4 3.2.3 Mg(AlH4)2 and Ca(AlH4)2 3.3 Amides 3.4 Metal Borohydrides 3.5 Destabilization of High Desorption Temperature Hydrides by (Nano)Compositing 3.5.1 MgH2–LiAlH4 Composite System 3.5.2 MgH2–NaAlH4 Composite System 3.5.3 MgH2–NaBH4 Composite System References Complex Hydrides 3.1 170 174 196 196 198 204 206 206 213 223 231 240 Carbons and Nanocarbons 291 4.1 4.2 291 294 294 295 Diamond and Nanodiamonds Graphene, Ordered Graphite, and Nanographites 4.2.1 Graphene 4.2.1.1 In-Plane σ and Out-of-Plane π Bonding 4.2.1.2 Van der Walls Interplanar and Intermolecular Interactions 4.2.1.3 Physisorption of Hydrogen on Carbons 4.2.1.4 Chemisorption of Hydrogen on Carbons 4.2.2 Graphitic Nanofibers, Whiskers, and Polyhedral Crystals 4.2.3 Graphite 4.3 Disordered and Active Carbons 4.3.1 Disordered Graphites and Mechanically-Activated Carbons 177 179 181 182 183 183 183 253 255 265 270 281 296 297 298 299 299 301 301 5.2 Complex Hydrides 323 recharged offboard after being depleted This could be an alternative hydrogen storage and delivery solution for mobile applications The second simple metal hydride of some good potential for further development is AlH3 As reviewed in Sect 2.4, the major advantages of this hydride include high gravimetric capacity, low temperature desorption range of 100–150°C, accompanied by reasonable kinetics for a catalyzed AlH3, and a very simple decomposition reaction to just purify Al and H2 in exactly the same manner as for MgH2 Disadvantages of AlH3 are a very costly conventional organometallic synthesis and the presence of a large number of polymorphs that may affect the conditions of desorption In reality, such a large number of polymorphs relates to the less than perfect organometallic synthesis It seems that the most important research focus would be on the development of inexpensive and fast bulk synthesis method of AlH3 Also, finding more effective catalysts would be an important research task Regarding intermetallic-based hydrides, there is no hydride in this group that would be even remotely close to any commercial vehicular application An interesting hydride is Mg2FeH6, whose great advantages are relative ease of synthesis in hydrogen alloying mills, better aging properties and its mechano-chemical reversibility by reactive mechanical alloying (Sect 3.1.2) Although providing the storage capacity that is inferior to MgH2 and thus not considered for any serious storage for vehicular application, it is most likely the most ideal candidate for thermochemical thermal energy storage devices ([40] in Sect 3.1.2) 5.2 Complex Hydrides In the alanate group, NaAlH4 is one of the most extensively researched hydride Its desorption parameters are now quite close to the US DOE targets (Sect 3.2.1) and it is reversible under a reasonable temperature–pressure range, which is a great asset of a hydride, as considered for onboard storage However, its hydrogen capacities are far too low for any mobile application In our opinion, if a good engineering design could result in a reservoir based on nanostructured, catalyzed MgH2, this would be a far better solution than using NaAlH4 as a storage medium Other hydride in this group that has some potential for a good storage medium is LiAlH4 Nanostructured and catalyzed LiAlH4 can desorb quite a large quantity of H2 with reasonable kinetics within a temperature range 150–200°C (Sect 3.2.2) It is quite possible that more research could improve its properties even further However, the fact that this hydride is based on Li might be a substantial drawback Li is a relatively rare element and relatively expensive by comparison with more common metallic elements Alanates of Mg and Ca such as Mg(AlH4)2 and Ca(AlH4)2, respectively, are based on much more abundant and rather inexpensive elements However, in comparison to NaAlH4 and LiAlH4, the knowledge about their efficient synthesis and hydrogen storage properties is miniscule They still deserve more intensive research efforts 324 Summary In the group of amides (Sect 3.3), we not see any single-phase amide that would give any hope for future vehicular storage Only mixtures of amides with other hydrides (e.g., MgH2) show slightly improved storage properties However, a complexity of these reactions between two dissimilar hydrides, a relatively small amount of hydrogen desorbed and a continuous presence of larger or smaller quantities of NH3, which is detrimental to the PEM membranes, make this system less promising than the others In addition, LiNH2 and Li2NH used in these reactions have the same drawback as LiAlH4, i.e., they contain relatively expensive Li, as discussed earlier In the metal borohydrides group (Sect 3.4), there is no apparent hydride that would be of the same interest for hydrogen storage as the few alanates described earlier A success was achieved in developing a simple rule that shows that metal borohydrides with low Pauling electronegativities (