Hydrogen is the only fuel for fuel-cells. It may be stored pure onboard the vehicle, but this approach is difficuft. It is preferable to attach hydrogen to other elements to form a hydrogen carrier, which will be cracked onboard to feed the fuel-cell. This paper explains the concept of hydrogen carriers, details their preferred characteristics, and compares thoroughly the available candidates. The most significant issues influencing the choice of a hydrogen carrier are: well-to-wheel and onboard energy efficiency, hydrogen energy density, reforming, renewability, safety. The well-to-wheel efficiency requirement eliminates synthetic gasoline. All fossil carriers are not to be considered because they are not renewable. Hydrazine is too dangerous. The intelligent choice is between methanol and ammonia. Methanol certainly presents the highest well-to-wheel efficiency. The well-to-wheel efficiency of ammonia is more difficult to assess, partly because until recently ammonia has not been considered for its energy content but as a fertilizer. The production of ammonia by the Haber-Bosch process certainly is less efficient than methanol, though it can be made totally renewable. It is much easier to extract hydrogen from ammonia than from methanol. The efficiency is expected to be higher and importantly the dynamic characteristics are much better. Methanol requires unrealistic warm-up times and its transient response is slow. In addition, the complexity of the piping in the case of methanol and the cost of the reformer are beyond compare with the simplicity of an ammonia cracker and its absence of requirement for expensive catalysts.
Investigation of hydrogen carriers for fuel-cell based transportation
Untersuchungen zu Wasserstoffträgern für brennstoffzellbasierte Fahrzeuge
2002
9 Seiten, 11 Quellen
Conference paper
English
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