Solid-State Hydrogen Storage

Materials and Chemistry

Gavin Walker

• Publisher: Woodhead Publishing
• Year: 2008
• ISBN:
  9781845694944
• Topic: Tecnología e ingeniería
• Subtopic: Recursos de energía renovable

Hydrogen fuel cells are emerging as a major alternative energy source in transportation and other applications. Central to the development of the hydrogen economy is safe, efficient and viable storage of hydrogen. Solid-state hydrogen storage: Materials and chemistry reviews the latest developments in solid-state hydrogen storage.Part one discusses hydrogen storage technologies, hydrogen futures, hydrogen containment materials and solid-state hydrogen storage system design. Part two reviews the analysis of hydrogen interactions including structural characterisation of hydride materials, neutron scattering techniques, reliably measuring hydrogen uptake in storage materials and modelling of carbon-based materials for hydrogen storage. Part three analyses physically-bound hydrogen storage with chapters on zeolites, carbon nanostructures and metal-organic framework materials. Part four examines chemically-bound hydrogen storage including intermetallics, magnesium hydride, alanates, borohydrides, imides and amides, multicomponent hydrogen storage systems, organic liquid carriers, indirect hydrogen storage in metal ammines and technological challenges in hydrogen storage.With its distinguished editor and international team of contributors, Solid-state hydrogen storage: Materials and chemistry is a standard reference for researchers and professionals in the field of renewable energy, hydrogen fuel cells and hydrogen storage.

• Assesses hydrogen fuel cells as a major alternative energy source
• Discusses hydrogen storage technologies and solid-state hydrogen storage system design
• Explores the analysis of hydrogen interactions including reliably measuring hydrogen uptake in storage materials

Part I

Introduction

Outline

Chapter 1: Hydrogen storage technologies

Chapter 2: Hydrogen futures: emerging technologies for hydrogen storage and transport

Chapter 3: Hydrogen containment materials

Chapter 4: Solid-state hydrogen storage system design

1

Hydrogen storage technologies

G. WALKER, University of Nottingham, UK

Publisher Summary

This chapter presents an introduction to the potential applications for hydrogen storage and provides an overview of the different technologies available for storing hydrogen. The various applications have different requirements in terms of the mass of hydrogen needed, volumetric capacity, gravimetric capacity and cost. The conventional hydrogen storage technologies are compressed gas and liquid storage. These hydrogen storage technologies are the current state-of-the-art, but more compact means of storing hydrogen are needed for portable and mobile applications, solid-state hydrogen storage materials would appear to be the most promising solution. The chapter describes these technologies and discusses alternative hydrogen storage material technologies. These materials can be split into three categories: physically bound hydrogen, where the hydrogen gas is physisorbed to a high surface area substrate; chemically bound hydrogen, where the hydrogen has formed a chemical compound with the substrate, for example, metal hydrides and complex hydrides, and the hydrogen is released through a thermal decomposition; and lastly hydrolytic evolution of hydrogen (sometimes referred to as chemical hydrides), a variation on chemically bound hydrogen where the hydrogen is released through a chemical reaction, typically a hydrolysis reaction, for example, the hydrolysis of metal powders and hydrides.

1.1 Introduction

There are significant concerns about the rising level of CO₂ emissions and the impact this is having on our environment (IPCC, 2007). The main source of the increase in CO₂ is from our increasing energy demands. Global energy needs are expanding rapidly: in 1973 the global demand for energy was 6128 Mtoe (million tonnes of oil equivalent), which almost doubled over the following three decades to 11435 Mtoe in 2005 (IEA, 2007a). Of this, the percentage contribution from countries in the Organization for Economic Cooperation and Development (OECD) fell from 61.3% to 48.5% while that for Asia and the Middle East more than doubled from 13.8% to 30.8% (IEA, 2007a). If energy policies do not change, energy scenarios predict demand will reach 17 100 Mtoe by 2030, with the developing countries contributing to 74% of that increase (IEA, 2007b). Fossil fuels currently account for 81% of the world’s energy needs and the scenario for 2030 shows little change in this percentage because of the reliance of the developing economies on coal. If we consider the energy consumption per capita we see a different picture emerging. Asia and the Middle East energy consumption is 1.0 toe/capita and that for OECD countries is 4.7 toe/capita. These results help illustrate that the ‘problem’ is not simply the increasing demand from the developing countries, but that the demand per capita for developed nations is almost five times that of the developing nations. This is a global problem, with developed countries needing to reduce their energy consumption per capita while enabling developing economies to expand (and the inevitable increase in energy consumption that that will result in).

In addition to limiting energy consumption, low-carbon energy technologies are needed to further reduce CO₂ emissions and alternatives to burning fossil fuels are required. Hydrogen has a high calorimetric value, with a lower heating value (LHV, i.e. the heat released upon combustion without recovery of the latent heat of vaporisation of any water produced) of 120 MJ kg⁻¹, compared with petrol, which is approximately a third of this at 43 MJ kg⁻¹. Hydrogen can be used for power generation either by combustion in for example an internal combustion engine (ICE), producing mechanical power, or electrochemically by using a fuel cell, producing electrical power. In both examples the hydrogen reacts with oxygen to form water. For fuel cells this is the only emission, but with ICE, NO_x can be formed if the combustion is too hot, hence ICE engines are often run lean to avoid this. Although hydrogen is a very abundant element, it exists on Earth primarily in combination with oxygen, as water. It can, though, be generated in a number of ways, such as electrolysis, reforming, fermentation and direct splitting of water either thermochemically or photocatalytically. If a renewable source of energy is used, the hydrogen will be CO₂ neutral. If fossil fuels are used then carbon capture and sequestration will be needed for there to be a significant CO₂ reduction. Hydrogen is thus a versatile energy carrier and is seen as an important part of the solution to lowering CO₂ emissions.

Hydrogen fuel cells have a range of potential applications as indicated in Fig. 1.1, operating from a few watts up to gigawatts. Hydrogen microfuel cells have great potential to power portable electronics such as laptops and mobile phones. The superior energy density of a hydrogen polymer electrolyte membrane (PEM) microfuel cell compared with a lithium ion rechargeable battery opens the way to longer battery lifetimes. Small fuel cells or ICE generation sets (0.1–1 kW size) offer back-up power when disconnected from the national grid (either from outages or when working in the field). For mobile applications, fuel cells could provide auxiliary power for electrical units such as air conditioning and refrigerators (e.g. for food delivery vehicles). Both PEM fuel cells and ICEs are competing technologies for the vehicle powertrain. There is also interest in using hydrogen fuel cells for distributed generation for domestic power and using solid oxide fuel cells or combined cycle gas turbines for small power stations in the MW to GW range.

1.1 A scheme indicating the power requirement and corresponding mass of hydrogen for various hydrogen applications.

Vehicle powertrain is seen as one of the biggest potential markets for hydrogen, replacing the use of petrol and diesel, but automotive hydrogen storage is also one of the most challenging applications. Transport accounts for 30.3% of global energy use (IEA, 2007a) and is the source of a significant amount of CO₂ emissions. Hydrogen, battery or most likely hybrid hydrogen/battery vehicles are the leading contenders for zero emission vehicles, an attraction for hydrogen vehicles is the combined high energy density and durability of hydrogen fuel cells in comparison with current battery technologies. The challenge with hydrogen is that it is a low-density gas and it is difficult to efficiently store enough hydrogen on-board a vehicle to give the vehicle an adequate range, e.g. c. 5 kg of hydrogen for a range of 500 km (Schlapbach and Züttel, 2001).

In the United States, the Department of Energy has set tough targets for the development of hydrogen vehicles (DOE, 2006). The targets for hydrogen storage systems (i.e. this includes the container and any balance-of-plant) are gi...

Table of contents

• Cover image
• Title page
• Table of Contents
• Related titles
• Copyright
• Contributor contact details
• Preface
• Part I: Introduction
• Part II: Analysing hydrogen interactions
• Part III: Physically bound hydrogen storage
• Part IV: Chemically bound hydrogen storage
• Index