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A hydrogen vehicle is a vehicle, such as an automobile or aircraft, which uses hydrogen]as its primary source of power for locomotion. These vehicles generally use the hydrogen in one of two methods: combustion or fuel-cell conversion:
- In combustion, the hydrogen is "burned" in engines in fundamentally the same method as traditional gasoline cars.
- In fuel-cell conversion, the hydrogen is turned into electricity through fuel cells which then power electric motors.
Hydrogen can be obtained through various thermochemical methods utilizing natural gas, coal (by a process known as coal gasification), liquefied petroleum gas, biomass (biomass gasification), or from water by electrolysis or by a process called thermolysis. A primary benefit of using pure hydrogen as a power source would be that it uses oxygen from the air to produce water vapor as exhaust. Another benefit is that, theoretically, the source of pollution created today by burning fossil fuels could be moved to centralized power plants, where the byproducts of burning fossil fuels can be better controlled. Hydrogen could also be produced from renewable energy sources with (in principle) no net carbon dioxide emissions. There are both technical and economic challenges to implementing wide-scale use of hydrogen vehicles; the timeframes in which such challenges may be overcome is unclear and a point of controversy.
Research and prototypes
Hydrogen does not come as a pre-existing source of energy like fossil fuels, but a carrier, much like a battery. It can be made from both renewable and non-renewable energy sources. A potential advantage is that it could be produced and consumed continuously, using solar, water, wind and nuclear power for electrolysis. Current hydrogen production methods utilizing hydrocarbons produce less pollution than would direct consumption of the same hydrocarbon fuel, gasoline, diesel or methane, in a modern internal combustion engine, but they produce more pollution than would use of that energy in plug-in hybrid electric vehicles. Hydrogen fuel cells generate less CO2 than conventional internal combustion engines if emissions throughout the entire fuel cycle are compared  and thus would contribute less to atmospheric radiative forcing per mile driven than such convention engines. Methods of hydrogen production that do not use fossil fuel would be more sustainable and would exhibit price volatility to a lesser degree than would methods relying on fossil fuels; however, currently such production is not economically feasible.
The recorded number of hydrogen powered public vehicles in the United States is 20 as of January 2007,  and a significant amount of research is underway to try to make the technology viable. The common internal combustion engine, usually fueled with gasoline (petrol) or diesel liquids, can be converted to run on gaseous hydrogen. However, the more energy efficient use of hydrogen involves the use of fuel cells and electric motors instead of a traditional engine. Hydrogen reacts with oxygen inside the fuel cells, which produces electricity to power the motors. One primary area of research is hydrogen storage, to try to increase the range of hydrogen vehicles, while reducing the weight, energy consumption, and complexity of the storage systems. Two primary methods of storage are metal hydrides and compression.
High-speed cars, buses, submarines, and rockets already can run on hydrogen, in various forms at great expense. NASA uses hydrogen to launch the Space Shuttles into space. There is even a working toy model car that runs on solar power, using a reversible fuel cell to store energy in the form of hydrogen and oxygen gas. It can then convert the fuel back into water to release the solar energy.
Hydrogen fuel cell difficulties
- For more details on this topic, see Fuel cell.
While fuel cells themselves are potentially highly energy efficient, and working prototypes were made by Roger E. Billings in the 1960s, at least four technical obstacles and other political considerations exist regarding the development and use of a fuel cell-powered hydrogen car.
Low volumetric energy
Hydrogen has a very low volumetric energy density at ambient conditions, equal to about one-third that of methane. Even when the fuel is stored as a liquid in a cryogenic tank or in a pressurized tank as a gas, the volumetric energy density (megajoules per liter) is small relative to that of gasoline. Because of the energy required to compress or liquefy the hydrogen gas, the supply chain for hydrogen has lower well-to-tank efficiency compared to gasoline. Some research has been done into using special crystalline materials to store hydrogen at greater densities and at lower pressures.
Instead of storing molecular hydrogen on-board, some have advocated using hydrogen reformers to extract the hydrogen from more traditional fuels including methane, gasoline, and ethanol. Many environmentalists are irked by this idea, as it promotes continued dependence on fossil fuels, at least in the case of gasoline and methane, unless it is derived from recently decayed biomass. However, vehicles using reformed gasoline or ethanol to power fuel cells could still be more efficient than vehicles running internal combustion engines, if the technology can be invented.
Fuel cell cost
Currently, fuel cells are costly to produce and fragile. However technologies currently under development may, in the future, result in robust and cost-efficient versions.
Hydrogen fuel cells were initially plagued by the high production costs associated with converting the gas to electricity ultimately required to power a hydrogen car. Scientists are also studying how to produce inexpensive fuel cells that are robust enough to survive the bumps and vibrations that all automobiles have to handle. Furthermore, freezing conditions are a major consideration because fuel cells produce water and utilize moist air with varying water content. Most fuel cell designs are fragile and can't survive in such environments. Also, many designs require rare substances such as platinum as a catalyst in order to work properly. Such a catalyst can be contaminated by impurities in the hydrogen supply. In the past few years, however, a nickel-tin catalyst has been under development which may lower the cost of cells.
Hydrogen production cost
- For more details on this topic, see Hydrogen production.
Chemically pure hydrogen is derived from a feed stock. The energy to drive this conversion can be produced from fossil fuels, etc. Thus, hydrogen is not a harvestable energy source comparable to fossil fuels, solar energy, and wind energy. The conversions to produce hydrogen will have inherent losses of energy that make hydrogen less advantageous as an energy carrier. Additionally, there are economic and energy penalties associated with packaging, distribution, storage and transfer of hydrogen. Current technologies use between 165% to 212% of the higher heating value to produce the hydrogen.
Hydrogen fuel cells are theoretically (without auxiliary devices to run the fuel cell) more efficient than internal combustion engines, achieving efficiencies of 50-60%. While some hydrogen fuel cells produce only water (SOFC and MCFC do produce CO2 but for MCFC it might be reused in the FC) as its byproduct, the production of hydrogen using fossil fuels creates emissions of greenhouse gases, which adds an additional environmental cost. This problem could be solved, however, by phasing out fossil fuels as an energy source and replacing them with clean energy sources, such as solar and wind.
Fourth, in order to distribute hydrogen to cars, the current gasoline fueling system would need to be replaced, or at least significantly supplemented with hydrogen fuel stations.
Although service life is coupled to cost, fuel cells have to be compared to existing machines with a service life in excess of twenty years. As of today, however, no medium or low temperature fuel cells have been tested for more than several hundred hours.
Since all energy sources have drawbacks, a shift into hydrogen-powered vehicles may require difficult political decisions on how to produce this energy. The United States Department of Energy has already announced a plan to produce hydrogen directly from generation IV reactors. These nuclear power plants would be capable of producing hydrogen and electricity at the same time. The main problem with the nuclear-to-hydrogen economy is that hydrogen is ultimately only an energy carrier. The costs associated with electrolysis and transportation and storage of hydrogen may make this method uneconomical in comparison to direct utilization of electricity. Electric power transmission is about 95% efficient and the infrastructure is already in place, so tackling the current drawbacks of electric cars or hybrid vehicles may be easier than developing a whole new hydrogen infrastructure that mimics the obsolete model of oil distribution. Continuing research on cheaper, higher capacity batteries are needed. Direct transmission through electric rails, for example in a guided vehicle configuration such as personal rapid transit, may turn out to make electric vehicles more economic than hydrogen fuel cell vehicles.
Recently, alternative methods of creating hydrogen directly from sunlight and water through a metallic catalyst have been announced. This may eventually provide an economical, direct conversion of solar energy into hydrogen, a very clean solution for hydrogen production..
Sodium borohydride (NaBH4) a chemical compound may hold future promise due to the ease at which hydrogen can be stored under normal atmospheric pressures in automobiles that have fuel cells.
United States President George W. Bush was optimistic that these problems could be overcome with research. In his 2003 State of the Union] address, he announced the U.S. government's hydrogen fuel initiative, which complements the President's existing FreedomCAR initiative for safe and cheap hydrogen fuel cell vehicles. Critics charge that focus on the use of the hydrogen car is a dangerous detour from more readily available solutions to reducing the use of fossil fuels in vehicles.
A 2006 article, "Hybrid Vehicles Gain Traction", in Scientific American (April 2006), co-authored by Joseph J. Romm and Prof. Andrew A. Frank, argues that hybrid cars that can be plugged into the electric grid (Plug-in hybrid electric vehicles), rather than hydrogen fuel-cell vehicles, will soon become standard in the automobile industry. To achieve lower emission goals, the power grid re-charging these vehicles will need to contribute significantly less emissions and wean themselves from fossil fuels for energy conversion.
Hydrogen internal combustion
Hydrogen internal combustion engine cars are different from hydrogen fuel cell cars. The hydrogen internal combustion car is a slightly modified version of the traditional gasoline internal combustion engine car. These hydrogen engines burn fuel in the same manner that gasoline engines do. As in hydrogen fuel cell vehicles, the volume of the vehicle that the tank occupies is significant. Research is underway to increase the amount of hydrogen that can be stored onboard, be it through high pressure hydrogen, cryogenic liquid hydrogen, or metal hydrides.
In 1807, François Isaac de Rivaz built the first hydrogen-fueled internal combustion vehicle. However, the design was very unsuccessful.
It is estimated that more than a thousand hydrogen-powered vehicles were produced in Germany before the end of the World War II prompted by the acute shortage of oil.
BMW's CleanEnergy internal combustion hydrogen car has more power and is faster than hydrogen fuel cell electric cars. A BMW hydrogen car (H2R) broke the speed record for hydrogen cars at 300 km/h (186 mi/h), making automotive history. Mazda has developed Wankel engines to burn hydrogen. The Wankel engine uses a rotary principle of operation, so the hydrogen burns in a different part of the engine from the intake. This reduces intake backfiring, a risk with hydrogen-fueled piston engines. However the major car companies like DaimlerChrysler and General Motors Corp, are investing in the slower (also in terms of load change), weaker, but more efficient hydrogen fuel cells instead. Ford Motor Company is investing in both fuel cell and hydrogen internal combustion engine research. Because of the large heat exchanger necessary for fuel cells and their limited load change and cold start capability, they are certainly first choice as range extender for battery electric vehicles.
A small proportion of hydrogen in an otherwise conventional internal combustion engine can both increase overall efficiency and reduce pollution. See Hydrogen fuel injection. Such a conventional car can employ an electrolizer to decompose water, or a mixture of hydrogen and other gases as produced in a reforming process. Since hydrogen can burn in a very wide range of air/fuel mixtures, a small amount of hydrogen can also be used to ignite various liquid fuels in existing internal combustion engines under extremely lean burning conditions. This process requires a number of modifications to existing engine air/fuel and timing controls. The American Hydrogen Associations has been demonstrating these conversions. Other renewable energy sources, like biodiesel, are also practical for existing automobile conversions, but come with their own host of problems.
Outside of specialty and small-scale uses, the primary target for the widespread application of fuel cells (hydrogen, zinc, other) is the transportation sector; however, to be economically and environmentally feasible, any fuel cell based engine would need to be more efficient from wellhead-to-wheel, than what currently exists.
USP # 6,126,794 ~ Apparatus for producing orthohydrogen and/or parahydrogen
USP # 4,936,961 ~ Method for the Production of a Fuel Gas
USP # 4,826,581 ~ Controlled Process for the Production of Thermal Energy from Gases...,
USP # 4,798,661 ~ Gas Generator Voltage Control Circuit,
USP # 4,613,304 ~ Gas Electrical Hydrogen Generator,
USP # 4,465,455 ~ Start-up/Shut-down for a Hydrogen Gas Burner,
USP # 4,421,474 ~ Hydrogen Gas Burner,
USP # 4,389,981 ~ Hydrogen Gas Injector System for Internal Combustion Engine USP # 4,702,894 ~ Cornish Hydrogen Generator,
Automobile and bus makers
- For more details on this topic, see List of fuel cell vehicles.
Many companies are currently researching the feasibility of building hydrogen cars. Funding has come from both private and government sources. In addition to the BMW and Mazda examples cited above, many automobile manufacturers have begun developing cars. These include:
- BMW — The BMW Hydrogen 7 is powered by a dual-fuel Internal Combustion Engine and with an Auxiliary power based on UTC Power fuel cell technology. The BMW H2R Concept speed record car is also power by an ICE. Both models use Liquid Hydrogen as fuel.
- DaimlerChrysler — F-Cell, a hydrogen fuel cell vehicle based on the Mercedes-Benz A-Class.
- Ford Motor – Focus FCV, a hydrogen fuel cell modification of the Ford Focus, and E-350 buses, which began being leased in late 2006.
- General Motors — multiple models of fuel cell vehicles including the Hy-wire and the HydroGen3
- Honda – currently experimenting with a variety of alternative fuels and fuel cells with experimental vehicles based on the Honda EV Plus, most notable the Honda FCX.
- Hyundai — Tucson FCEV, based on UTC Power fuel cell technology
- Mazda - RX-8, with a dual-fuel (hydrogen or gasoline) rotary-engine 
- Nissan — X-TRAIL FCV, based on UTC Power fuel cell technology.
- Morgan Motor Company – LIFEcar, a performance-oriented hydrogen fuel cell vehicle with the aid of several other British companies
- Toyota – The Toyota Highlander FCHV and FCHV-BUS are currently under development and in active testing.
- Volkswagen also has hydrogen fuel cell cars in development.
A few bus companies are also conducting hydrogen fuel cell research. These include:
- DaimlerChrysler, based on Ballard fuel cell technology
- Thor Industries (the largest maker of buses in the U.S.), based on UTC Power fuel cell technology
- Irisbus, based on UTC Power fuel cell technology
- Fuel Cell Bus Club
Supporting these automobile and bus manufacturers are fuel cell and hydrogen engine research and manufacturing companies. The largest of these is UTC Power, a division of United Technologies Corporation, currently in joint development with Hyundai, Nissan, and BMW, among other auto companies. Another major supplier is Ballard Power Systems. The Hydrogen Engine Center is a supplier of hydrogen-fueled engines.
Most, but not all, of these vehicles are currently only available in demonstration models and cost a large amount of money to make and run. They are not yet ready for general public use and are unlikely to be as feasible as plug in biodiesel hybrids.
There are, however, fuel cell powered buses currently active or in production, such as a fleet of Thor buses with UTC Power fuel cells in California, operated by SunLine Transit Agency. Perth, Australia is also participating in the trial with three fuel cell powered buses now operating between Perth and the port city of Fremantle. The trial is to be extended to other Australian cities over the next three years.
Mazda leased two dual-fuel RX-8s to commercial customers in Japan in early 2006, becoming the first manufacturer to put a hydrogen vehicle in customer hands. Ford began leasing E-350 shuttle buses in late 2006. BMW also plans to release its first publicly available hydrogen vehicle in 2008, as does Honda.
Los Altos High School in Hacienda Heights, California is the only high school that has built a hydrogen fuel cell car.
- For more details on this topic, see Hydrogen station.
Since the turn of the millennium, filling stations offering hydrogen have been opening worldwide, new are the home stations .