Other Means of Hydrogen Storage

In seeking to overcome the problems associated with hydrogen storage and distribution, many investigators have set out to use liquids that are rich in hydrogen such as gasoline or methanol as a hydrogen source. In contrast to pure hydrogen, these are compact (they contain, on a volume basis, more hydrogen than even liquid hydrogen), and are easy to store and handle. The possibility of generating hydrogen with more than 80% efficiency by on-board reforming of gasoline has been demonstrated. As the reforming produces a mixture of H2 and CO, the later must be separated and disposed of as CO2, adding to atmospheric levels of greenhouse gases. Also, as CO will poison the fuel cells, every trace must be removed. The reforming process is expensive and also challenging, because it involves high temperatures and needs considerable time to reach steady-state operational conditions. The advantage is that the distribution network for hydrocarbon fuels already exists, though this would not solve the problems of diminishing oil and gas resources. Methanol reformers operating at much lower temperatures (250-350 °C) [95], though still expensive, are more adaptable for vehicle on-board applications. The absence of any C-C bonds in methanol also greatly facilitates its reforming to hydrogen, and it is the fuel used currently to generate hydrogen in DaimlerChrysler's Necar 5 fuel cell demonstration vehicle. As a liquid, methanol - much like gasoline - can be distributed through the existing infrastructure including filling stations, with only minor modifications. Furthermore, methanol can be made from different sources, including the recycling of CO2 (see Chapter 11).

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