Hydrogen as a fuel

Sonja Studer, Samuel Stuck , and John D. Speight 

1 Tabulate the abundances of elements in seawater, given in the text, as atom % values (include H and O), and compare their rankings with those of the elements in the Earth s crust as given in Table 1.1. Suggest possible reasons for any differences in the rankings. 

2 Why are elemental hydrogen and helium, the two most abundant elements in the universe, not present in significant amounts in the Earth s atmosphere  

The Norton History of Chemistry. Norton, New York, 1993. 

Leicester, The Historical Background of Chemistry. Dover, New York, 1971. 

Hartley, Studies in the History of Chemistry. Oxford Univ. Press, London, 1971. 

The first application of hydrogen as a fuel was starting in the late 18th century when it was tried to utilize the physical property of low density for flying balloons. The Frenchman Charles realized in 1783 the first liftoff of an H2 balloon ( Charliere ) filled with 40 m of H2 which he produced by spilling sulfuric acid onto iron. The balloon traveled a distance of 25 km in a height of up to about 1 km. 

Catalytic or flameless combustion of hydn en exhibits many advantages in comparison with flame combustion. It occurs at low temperatures (ambient - 800 K), is safe and leads to a very high conversion of the burning gas (99.9 %). The NOX formation which usually occurs in conventional combustion at temperatures of about 1700 K, is here almost completely suppressed. The catalytic combustion in diffusion burners (Fig. 7-2) occurs in the presence of small amounts of Pt or Pd catalysts. It is adequate, e.g., for kitchen appliances such as cooker, oven, water heater, space heater. Drawbacks are the possible non-uniformity of the temperature distribution at die catalyst surface, rapid changes in the operational state, and relatively small heat flux densities [47]. 

The fuel cell is an energy conversion device that works in reverse of electrolysis. In the cell, the energy of a fuel is directly converted by an electrochemical reaction 

A detailed description of all different kinds of fuel cells, their techniques and applications can be found in [30]. 

Various fuel cell types have been developed usually classified according to the electrolyte used. In Table 7-2, fuel cell types are listed with their operating temperatures and anode / cathode reactions. 

If hydrogen is to be employed as an energy vector and a non-polluting fuel, then it is necessary to take account of its basic physical properties. Hydrogen is a colourless, odourless, tasteless and non-toxic gas. It is the lightest of all molecules (molecular weight = 2.016) and, consequently, has a density of only 

7% of the density of air. Liquid hydrogen also has a low density of 70.8 kgm (7% of that of water). The liquid has a very low boiling point (20.3 K) and therefore requires fairly sophisticated equipment to prepare and maintain it in this state. 

By virtue of its exceptionally low density, hydrogen has the best energy-to-weight ratio ( heating value ) of any fuel, but its energy-to-volume ratio is poor (Table 1.4). The thermodynamic heat of combustion of hydrogen (its heating value) equates to the standard heat of formation (A//f) of the product water, i.e.. 

Extensive experience has been gained in the safe handling of liquid hydrogen, both in physics laboratories and, on a tonnage scale, for use in the space industry as a rocket fuel. No insuperable technical problems are encountered. The specialized equipment is, however, very costly and is one reason why liquid hydrogen has not been seriously considered as a fuel outside the space industry, where its low density is a particularly valuable property. Experimentally, liquid hydrogen has been employed as a fuel in automotive applications and there has been some preliminary consideration of using it as an aircraft fuel see Section 7.3, Chapter 7. 

The most obvious response to this problem is to reduce the volume of the hydrogen by some physical change, for example by compressing the gas in cylinders, or by supplying vehicles with a vacuum-insulated fuel tank, which can be loaded with, and store, liquid hydrogen. 

A very different type of system is being explored by an Anglo-Swiss research project launched in 1991. It uses a version of Reaction 5.5  

Toluene, on the left, is a liquid that boils at 111 °C, and we draw it here as one of its two resonance structures, both of which include a ring containing three C=C bonds. 

They undergo the same process as the C=C bonds in Reaction 5.5, and are converted to C—C single bonds. 

Another new development in the use of hydrogen as a fuel is in the fuel cell car developed by Daimler-Chrysler, the NECAR. This prototype electric car uses hydrogen as a fuel for a fuel cell in which the energy of hydrogen oxidation to water is converted to electricity. The car runs on a mixture of methanol and water. Using a relatively low-temperature catalyst, these substances react to produce hydrogen and carbon dioxide, in the gas phase  

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Concerns about global climate change have motivated new interest in low-carbon or noncarbon fuels. Recent rapid progress and industrial interest in low-temperature fuel cells (which prefer hydrogen as a fuel) for transportation and power applications have also led to a reexamination of hydrogen as a fuel. 

Cammack R, Frey M, Robson R. 2001. Hydrogen as a Fuel Learning from Nature. London Taylor Francis. 

Source Adapted from Kirk-Othmer Encyclopedia of Chemical Technology. Fundamentals and Use of Hydrogen as a Fuel. 3rd ed., Vol. 4, Wiley, New York, 1992, 631p. 

Replacing petroleum products with hydrogen as a fuel for transportation has the following advantages and disadvantages. 

Public knowledge of hydrogen technology is still relatively low (Fuhrmann and Bleischwitz, 2007). Many people still do not know the difference or have difficulties with separating the usage of hydrogen as a fuel from the fuel cell, which is a device to turn hydrogen into useful power. 

Positive impacts of hydrogen vehicles can be expected in impacts of climate changes, local emissions and noise. These impacts will be discussed in detail in the following sections. However, some new problems could be identified by the introduction of hydrogen as a fuel in the transport sector, which will be treated later on in this chapter. 

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