The Hydrogen Economy

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The historical trend toward decarbonization reflects the contention by many energy forecasters that hydrogen will be the fuel of choice in the future. These forecasters believe that power plants and motor vehicles will run on hydrogen. The economies that emerge will depend on hydrogen and are called hydrogen economies. The concept of a hydrogen economy is not new. The use of hydrogen as a significant fuel source driving a national economy was first explored in the middle of the 20th century as a complement to the adoption of large-scale nuclear electric generating capacity. Concerns about global climate change and the desire to achieve sustainable development have renewed interest in hydrogen as a fuel.

A future that depends on hydrogen is not inevitable. Hydrogen economies will require the development of improved technologies for producing, storing, transporting, and consuming hydrogen. We have already discussed some of the challenges involved in the production of hydrogen. As another example of the technological challenges that must be overcome in a transition to a hydrogen economy, let us consider the storage of hydrogen.

Hydrogen can be stored in the liquid or gaseous state, but it must be compressed to high pressures or liquefied to achieve reasonable storage volumes because of the low density of the diatomic hydrogen molecule. The energy content of hydrogen gas is less than the energy contained in methane at the same temperature and pressure. The volumetric energy density of liquid hydrogen is approximately 8700 megajoules/meter3. This is about one third the volumetric energy density of gasoline. The relatively low volumetric energy density of hydrogen creates a storage problem if we want to store hydrogen compactly in vehicles.

Researchers have learned that hydrogen can be stored effectively in the form of solid metal hydrides. A metal hydride is a metal that absorbs hydrogen. The hydrogen is absorbed into the spaces, or interstices, between atoms in the metal. According to M. Silberberg [1996, page 246], metals such as palladium and niobium "can absorb 1000 times their volume of H2 gas, retain it under normal condi-

tions, and release it at high temperatures." This form of storage may be desirable for use in hydrogen-powered vehicles. A model of a car using hydrogen fuel cells is shown in Figure 7-4.

tions, and release it at high temperatures." This form of storage may be desirable for use in hydrogen-powered vehicles. A model of a car using hydrogen fuel cells is shown in Figure 7-4.

Figure 7-4. Hydrogen Fuel Cell Car, Denver, Colorado Exhibit

Hydrogen can be hazardous to handle. A spectacular demonstration of this fact was the destruction of the German zeppelin Hindenburg. The Hindenburg used hydrogen for buoyancy. In 1937, the Hindenburg burst into flames while attempting a mooring in Lakehurst, New Jersey. At the time, people believed that the hydrogen in the Hindenburg was the cause of the explosion. Addison Bain, at the end of the 20th century, showed that the chemical coating on the outside of the zeppelin was the cause of the explosion. When the chemical coating ignited, the hydrogen began to burn. Today, lighter-than-air ships use less flammable gases such as helium.

Hydrogen forms an explosive mixture with air when the concentration of hydrogen in air is in the range of 4% to 75% hydrogen. For comparison, natural gas is flammable in air when the concentration of natural gas in air is in the range of 5% to 15% natural gas. Furthermore, the energy to ignite hydrogen-air mixtures is approximately one-fifteenth the ignition energy for natural gas-air or gasoline-air mixtures. The flammability of hydrogen in air makes it possible to consider hydrogen a more dangerous fuel than natural gas. On the other hand, the low density of hydrogen allows hydrogen to dissipate more quickly into the atmosphere than a higher density gas such as methane. Thus, hydrogen leaks can dissipate more rapidly than natural gas leaks. Adding an odorant to the gas can enhance the detection of gas leaks.

The environmental acceptability of hydrogen fuel cells depends on how the hydrogen is produced. If a renewable energy source such as solar energy is used to generate the electricity needed for electrolysis, vehicles powered by hydrogen fuel cells would be relatively clean since hydrogen combustion emits water vapor. Unfortunately, hydrogen combustion in air also emits traces of nitrous oxide compounds. Nitrogen dioxide contributes to photochemical smog and can increase the severity of respiratory illnesses.

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Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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Responses

  • ailie
    How much increase in hydrogen in air would be caused by hydrogen economy?
    25 days ago

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