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Rechargeable magnesium (Mg) battery has been considered as a promising candidate for future battery generations because of its potential high-energy density, its safety features and low cost. The challenges lying ahead for the realization of Mg battery in general are to develop proper electrolytes fulfilling a multitude of requirements and to discover cathode materials enabling high-energy Mg batteries. The combination of Mg anode with a sulfur cathode is one of the promising electrochemical couples due to its advantages of safety, low costs, and a high theoretical energy density of over 3200 Wh/L. However, the research on magnesium–sulfur (Mg–S) battery is just at its beginning and the development of suitable electrolytes has been the key challenge for further improvement, and, thus, in the focus of recent research. In this review, we highlight the recent progress achieved in Mg electrolytes and Mg–S batteries and discuss the major technical issues, which must be resolved for the improvement of Mg–S batteries.
Cerium in various chemical forms was introduced into NaAlH4 to study the hydrogen sorption properties of the resulted material. Although all the Ce precursors tested in this work resulted in a reversible hydrogen storage material, an immediate enhancement in the desorption kinetics could be achieved by a heating treatment, resulting in the in situ formation of cerium aluminide (CeAl4) in the material. While the use of CeAl4 instead of CeCl3 can increase the hydrogen capacity by bypassing the formation of the ineffective NaCl, the highest capacity of 4.9 wt% was obtained from NaAlH4 doped directly with commercial metallic cerium, which may provide a much simplified process for a possible up-scaling preparation of this hydrogen storage material.
The need for new and sustainable energy technologies is particularly urgent in the transport sector, where energy demands keep growing and give rise to significant global and local pollution. Hydrogen is expected to play a key role in this development (Satyapal et al.,2006). Hydrogen storage is regarded as one of the most critical issues that has to be solved before a technically and economically viable hydrogen economy can be established. In fact, without effective storage systems, a hydrogen economy will be difficult to achieve. One of the most challenging applications in this field is hydrogen storage for mobile applications. This chapter addresses the current state of the various on-board hydrogen-storage systems.
Requirements for hydrogen storage
In hydrogen-fuelled passenger cars, 4–5 kg (130–160 kWh) H2 must be stored in a small, preferably lightweight, tank in order to achieve a driving range of 500 km (i.e., 80–125 km/kg H2). However, whereas the gravimetric energy density of hydrogen is extremely high, the volumetric storage density of the lightweight gas is low. At ambient temperature and pressure, 5 kg H2 would fill a ball 5 m in diameter, which is roughly comparable to the volume of an inflated hot-air balloon. Consequently, the most important technical and economic challenges to be overcome in a practical hydrogen-storage system are the storage density related to the system (including tank, heat management, and valves), the costs of the system, its safety, a short refuelling time, and the ability to deliver enough hydrogen during the driving cycle.
With the expected increasing significance of hydrogen as a universal chemical and as an energy vector, its physical and thermodynamic properties are undergoing extensive investigation. To provide a basis of understanding for the themes covered in the remainder of the book, this chapter briefly describes the fundamental properties of hydrogen.
Discovery and occurrence
Named by a French chemist, Lavoisier, hydrogen (H) is the first chemical element of the periodic table of elements with an atomic number of one. At standard temperature and pressure, hydrogen is a colourless, tasteless, odourless and easily flammable gas. With its atomic mass of 1.00797 g/mol, hydrogen is the lightest element. The British scientist, Henry Cavendish, was the first to identify H as a distinct element in 1766, publishing precise values for its specific weight and density (NHA, 2007).
Hydrogen is also one of the most abundant chemical elements in the Universe (70–80 wt.% H2 content); more than 50 wt.% of the Sun consists of hydrogen. However, on Earth it mostly occurrs naturally in the form of chemical compounds, most frequently water and hydrocarbons. As a gas in its free state, hydrogen is very rare (1 ppm by volume in the Earth's atmosphere), owing to its light weight, and it can only be found in natural gas and some volcanic gases, as well as trapped in small quantities in some minerals and rocks (Ullmann, 2003).
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