Although the demand for renewable resources is growing, the world continues to meet much of its energy needs using oil. Oil's byproducts fuel cars, ships, and planes, and in much of the world it is burned to produce electricity. Although oil is a very useful substance, the earth contains only a limited quantity, and the earth's inhabitants, both plants and animals, are harmed directly and indirectly when oil is extracted from the ground and when its byproducts are combusted for energy. In order to preserve the environment and meet the energy needs of a growing world population, people must substitute alternative substances in place of oil.
Despite humanity's need to transition away from using oil, few alternatives can be obtained, processed, stored, and used as cheaply and as easily as oil, and in quantities that match the demand for oil. Thus, oil remains an essential fuel in economies around the world. A key factor in oil's dominance throughout the world is the high energy density per volume of its byproducts, which enables hydrocarbons to be transported and stored at energy capacities that meet society's demands. Gasoline, for instance, contains about 44.4 megajoules per kilogram (“MJ/kg”), and diesel fuel contains about 45.4 MJ/kg. Hydrogen and methane, which are both readily available fuel alternatives to gasoline and diesel, contain about 143 MJ/kg and 55.6 MJ/kg, respectively. However, hydrogen and methane are gasses at room temperature and atmospheric pressure, and therefore far less dense than liquid hydrocarbons like gasoline and diesel. Consequently, hydrogen gas contains only about 0.01079 megajoules per liter (“MJ/l”) and methane gas contains only about 0.0378 MJ/l, while gasoline contains about 32 MJ/l and diesel contains about 38.6 MJ/l. If gasses like hydrogen and methane are to replace hydrocarbons on a world level, they must be able to be stored in a manner that compensates for their low energy densities by volume.
Numerous methods have been developed for storing hydrogen and other gasses at higher energy densities per volume. A first approach is to store the gas at a very high pressure. While this method is useful for many applications, including transporting gasses through pipelines, it is infeasible for most typical applications because substantial energy is wasted compressing the gas. Also, a tank capable of withstanding high pressure is too heavy for most vehicles, planes, or other machines that might be fueled by the compressed gas. Another approach is to store the gas as a liquid or slush. This approach suffers from a number of drawbacks, including extensive storage costs. For example, like hydrogen, one of the most viable alternatives to oil, many gasses boil at very low temperatures, meaning they must be cryogenically stored, and cooling the gas to a liquid or slush and keeping it cooled would waste a substantial amount of energy.
Hydrogen and other gasses may also be stored at higher energy densities per volume as an absorbed substance or as a metal hydride. Unfortunately, many metal hydrides include rare earth metals and have energy densities per weight that are lower than hydrocarbons because of the heavy metals used for storage. Additionally, materials that receive hydrogen, such as activated carbon granules, carbonized tissues, zeolites, and hydride particles, are poor thermal conductors, meaning that the rate at which these materials may be cooled to absorb a gas and the rate that these materials may be heated to release a gas are both limited. These materials may also degrade or produce dust and debris, which may contaminate released gas and clog delivery conduits, fittings, valves, and filters of a storage system.
Furthermore, substantial energy is wasted transporting oil and its byproducts to locations at which the oil is refined or its byproducts are consumed while large quantities of renewable resources that can be converted into fuels, such as farm waste, are wasted. Additionally, when hydrocarbons are burned, their byproducts are generally discarded. These byproducts are warming the earth's atmosphere. Historically, it has been difficult to store, process, or filter the byproducts of hydrocarbons for later productive use. For example, a vehicle manufacturer may find it impractical to store the exhaust from a combustion engine because the exhaust occupies such a large volume. Similarly, while filters exist that remove particulate matter from hydrocarbon byproducts, it is difficult to filter a first compound from a second compound or to react a byproduct with another compound to produce a useful compound in a limited amount of space. As a result, the byproducts of hydrocarbons are released into the air, wasting a potentially fruitful energy source and polluting the earth.