What is Hydrogen Fuel?

Hydrogen is the simplest and most common element in the universe. It has the highest energy content per unit of weight—52,000 British Thermal Units (Btu) per pound (or 120.7 kilojoules per gram)—of any known fuel. Moreover, when cooled to a liquid state, this low-weight fuel takes up 1/700 as much space as it does in its gaseous state. This is one reason hydrogen is used as a fuel for rocket and spacecraft propulsion, which requires fuel that is low-weight, compact, and has a high energy content. 

In a free state and under normal conditions, hydrogen is a colorless, odorless, and tasteless gas. The basic hydrogen (H) molecule exists as two atoms bound together by shared electrons. Each atom is composed of one proton and one orbiting electron. Since hydrogen is about 1/14 as dense as air, some scientists believe it to be the source of all other elements through the process of nuclear fusion. It usually exists in combination with other elements, such as oxygen in water, carbon in methane, and in trace elements as organic compounds. Because it is so chemically active, it rarely stands alone as an element. 

When burned (or combined) with pure oxygen, the only by products are heat and water. When burned (or combined) with air, which is about 68% nitrogen, some oxides of nitrogen (Nitrogen Oxides or NOx) are formed. Even then, burning hydrogen produces less air pollutants relative to fossil fuels. 

Producing Hydrogen bound in organic matter and in water makes up 70% of the earth's surface. 

More About Hydrogen Fuel

Breaking up these bonds in water allows us produce hydrogen and then to use it as a fuel. There are numerous processes that can be used to break these bonds. Described below are a few methods for producing hydrogen that are currently used, or are under research and development. 

Most of the hydrogen now produced in the United States is on an industrial scale by the process of steam reforming, or as a byproduct of petroleum refining and chemicals production. Steam reforming uses thermal energy to separate hydrogen from the carbon components in methane and methanol, and involves the reaction of these fuels with steam on catalytic surfaces. The first step of the reaction decomposes the fuel into hydrogen and carbon monoxide. Then a "shift reaction" changes the carbon monoxide and water to carbon dioxide and hydrogen. These reactions occur at temperatures of 392° F (200 ° C) or greater. 

Another way to produce hydrogen is by electrolysis. Electrolysis separates the elements of water—H and oxygen (O)—by charging water with an electrical current. Adding an electrolyte such as salt improves the conductivity of the water and increases the efficiency of the process. The charge breaks the chemical bond between the hydrogen and oxygen and splits apart the atomic components, creating charged particles called ions. The ions form at two poles: the anode, which is positively charged, and the cathode, which is negatively charged. Hydrogen gathers at the cathode and the anode attracts oxygen. A voltage of 1.24 Volts is necessary to separate hydrogen from oxygen in pure water at 77° Fahrenheit (F) and 14.7 pounds per square inch pressure [25° Celsius (C) and 1.03 kilograms (kg) per centimeter squared.] This voltage requirement increases or decreases with changes in temperature and pressure. 

The smallest amount of electricity necessary to electrolyze one mole of water is 65.3 Watt-hours (at 77° F; 25 degrees C). Producing one cubit foot of hydrogen requires 0.14 kilowatt-hours (kWh) of electricity (or 4.8 kWh per cubic meter). 

Renewable energy sources can produce electricity for electrolysis. For example, Humboldt State University's Schatz Energy Research Center designed and built a stand-alone solar hydrogen system. The system uses a 9.2 kilowatt (KW) photovoltaic (PV) array to provide power to compressors that aerate fish tanks. The power not used to run the compressors runs a 7.2 kilowatt bipolar alkaline electrolyzer. The electrolyzer can produce 53 standard cubic feet of hydrogen per hour (25 liters per minute). The unit has been operating without supervision since 1993. When there is not enough power from the PV array, the hydrogen provides fuel for a 1.5 kilowatt proton exchange membrane fuel cell to provide power for the compressors. 

Steam electrolysis is a variation of the conventional electrolysis process. Some of the energy needed to split the water is added as heat instead of electricity, making the process more efficient than conventional electrolysis. At 2,500 degrees Celsius water decomposes into hydrogen and oxygen. This heat could be provided by a concentrating solar energy device. The problem here is to prevent the hydrogen and oxygen from recombining at the high temperatures used in the process. 

Thermochemical water splitting uses chemicals such as bromine or iodine, assisted by heat. This causes the water molecule to split. It takes several steps—usually three—to accomplish this entire process. 

Photoelectrochemical processes use two types of electrochemical systems to produce hydrogen. One uses soluble metal complexes as a catalyst, while the other uses semiconductor surfaces. When the soluble metal complex dissolves, the complex absorbs solar energy and produces an electrical charge that drives the water splitting reaction. This process mimics photosynthesis. 

The other method uses semiconducting electrodes in a photochemical cell to convert optical energy into chemical energy. The semiconductor surface serves two functions, to absorb solar energy and to act as an electrode. Light-induced corrosion limits the useful life of the semiconductor. 

Researchers at the University of Tennessee and U.S. Department of Energy's (DOE) Oak Ridge National Laboratory are researching ways to use photosynthesis to produce hydrogen from sunlight. The researchers extracted two photosynthetic complexes from spinach plants; called Photosystem I and Photosystem II. The two work together to produce carbohydrates for the plant. By attaching platinum atoms to the Photosystem I complexes, the researchers were able to produce hydrogen from visible light. Unfortunately, the process required the use of an added chemical that makes the overall process impractical, but the achievement shows potential. The researchers are working to combine the platinum-Photosystem I complexes with the Photosystem II complexes, forming a molecular system that can convert light and water directly into hydrogen, without help from an added chemical. 

Biological and photobiological processes can use algae and bacteria to produce hydrogen. Under specific conditions, the pigments in certain types of algae absorb solar energy. The enzyme in the cell acts as a catalyst to split the water molecules. Some bacteria are also capable of producing hydrogen, but unlike algae they require a substrate to grow on. The organisms not only produce hydrogen, but can clean up pollution as well. 

Research funded by DOE has led to the discovery of a mechanism to produce significant quantities of hydrogen from algae. Scientists have known for decades that algae produce trace amounts of hydrogen, but had not found a feasible method to increase the production of hydrogen. Scientists from the University of California (UC), Berkeley, and the U.S. DOE's National Renewable Energy Laboratory found the key. After allowing the algae culture to grow under normal conditions, the research team deprived it of both sulfur and oxygen, causing it to switch to an alternate metabolism that generates hydrogen. After several days of generating hydrogen, the algae culture was returned to normal conditions for a few days, allowing it to store up more energy. The process could be repeated many times. Producing hydrogen from algae could eventually provide a cost-effective and practical means to convert sunlight into hydrogen. 

Another source of hydrogen produced through natural processes is methane and ethanol. Methane (CH4) is a component of "biogas" that is produced by anaerobic bacteria. Anaerobic bacteria occur widely throughout the environment. They break down or "digest" organic material in the absence of oxygen and produce biogas as a waste product. Sources of biogas include landfills, and livestock waste and municipal sewage treatment facilities. Methane is also the principal component of "natural gas" (a major heating and power plant fuel) produced by anaerobic bacteria eons ago. Ethanol is produced by the fermentation of biomass. Most fuel ethanol produced in the United States is made from corn. 

Chemical engineers at the University of Wisconsin-Madison have developed a process to produce hydrogen from glucose, a sugar produced by many plants. The process shows particular promise because it occurs at relatively low temperatures, and can produce fuel-cell-grade hydrogen in a single step. Glucose is manufactured in vast quantities from corn starch, but can also be derived from sugar beets or low-cost waste streams like paper mill sludge, cheese whey, corn stover or wood waste. 

The United States, Japan, Canada, and France have investigated thermal water splitting, a radically different approach to creating hydrogen. This process uses heat of up to 5,430°F (3,000°C) to split water molecules. 

Potential Uses for Hydrogen

When properly stored, hydrogen as a fuel burns in either a gaseous or liquid state. Motor vehicles and furnaces can be converted to use hydrogen as a fuel. Hydrogen has actually been used in the transportation, industrial, and residential sectors in the United States for many years. Many people in the late 19th century burned a fuel called "town gas," which is a mixture of hydrogen and carbon monoxide. Several countries, including Brazil and Germany, still distribute this fuel. Hydrogen was used in early "hot-air" balloons, and later in airships (dirigibles) during the early 1900's. Gaseous hydrogen was used in 1820 as fuel for one of the earliest internal combustion engines. The U.S. Air Force had a secret, multi-million dollar program during the 1950's, code-named "Suntan," to develop hydrogen as a fuel for airplanes. Currently, industries use large quantities of hydrogen for refining petroleum, and for producing ammonia and methanol. The Space Shuttle uses hydrogen as fuel for its rockets. Automobile manufacturers have developed hydrogen-powered cars. 

Burning hydrogen creates less air pollution than gasoline or diesel. Hydrogen also has a higher flame speed, wider flammability limits, higher detonation temperature, burns hotter, and takes less energy to ignite than gasoline. This means that hydrogen burns faster, but carries the danger of pre-ignition and flashback. While hydrogen has its advantages as a vehicle fuel it still has a long way to go before it can be used as a substitute for gasoline. This is mainly due to the investment required to develop a hydrogen production and distribution infrastructure. 

However, things are getting started in this regard. Vehicle manufacturers Honda and BMW have set up hydrogen fueling stations as part of their efforts to develop fuel cell powered cars. At Honda's research and development center in Torrance, California, a PV array electrolyses hydrogen from water. The array generates enough hydrogen to power one fuel-cell vehicle. Additional power from the power grid is used to increase the hydrogen production capacity. The new station is supporting Honda's fuel cell vehicle development program for hydrogen production, storage, and fueling. Honda and a fuel cell developer are also working together on a "home" hydrogen refueling system for fuel cell vehicles. BMW opened a hydrogen fueling station at the company's engineering and emissions control test center in Oxnard, California. BMW is taking a different approach than most car companies, burning hydrogen directly in advanced internal-combustion engines, and is testing these vehicles at the Oxnard facility. 

The California Fuel Cell Partnership (CaFCP) is also building a hydrogen infrastructure. The CaFCP commissioned its first "satellite" hydrogen fueling system in late October 2002, in Richmond, California, about 70 miles from the CaFCP headquarters and a primary refueling facility in West Sacramento. This extends the range over which the CaFCP's prototype fuel cell vehicles can be driven. The fueling system uses electrolysis to generate hydrogen from water and includes a storage unit capable of holding 104 pounds (47 kilograms) of hydrogen. It is capable of fueling a small fleet of vehicles and requires only one or two minutes per refueling. 

In November 2002, the world's first hydrogen energy station that can provide fuel for vehicles and also produce electricity opened in Las Vegas Nevada. The station is located in the city's vehicle maintenance and operation service center. It combines an on-site hydrogen generator, compressor, liquid and gaseous hydrogen storage tanks, dispensing systems, and a stationary fuel cell. It is capable of dispensing hydrogen, hydrogen-enriched natural gas, and compressed natural gas. DOE is also working with the city to convert municipal vehicles to operate on hydrogen. 

Fuel cells are a type of technology that use hydrogen to produce useful energy. In fuel cells, electrolysis is reversed by combining hydrogen and oxygen through an electrochemical process, which produces electricity, heat, and water. The U.S. space program has used fuel cells to power spacecraft for decades. Fuel cells capable of powering automobiles and buses have been and are being developed. Several companies are developing fuel cells for stationary power generation. Most major automobile manufacturers are developing fuel cell powered automobiles. 

Hydrogen could be considered a way to store energy produced from renewable resources such as solar, wind, biomass, hydro, and geothermal. For example, when the sun is shining, solar photovoltaic systems can provide the electricity needed to separate the hydrogen (as described above regarding Humboldt State University's Research Center). The hydrogen could then be stored and burned as fuel, or to operate a fuel cell to generate electricity at night or during cloudy periods. 

Storing Hydrogen

In order to use hydrogen on a large scale, safe, practical storage systems must be developed, especially for automobiles. Although hydrogen can be stored as a liquid, it is a difficult process because the hydrogen must be cooled to -423° Fahrenheit (-253° Celsius). Refrigerating hydrogen to this temperature uses the equivalent of 25% to 30% of its energy content, and requires special materials and handling. To cool one pound (0.45 kg) of hydrogen requires 5 kWh of electrical energy. 

Hydrogen may also be stored as a gas, which uses less energy than making liquid hydrogen. As a gas, it must be pressurized to store any appreciable amount. For large-scale use, pressurized Hydrogen gas could be stored in caverns, gas fields, and mines. The hydrogen gas could then be piped into individual homes in the same way as natural gas. Though this means of storage is feasible for heating, it is not practical for transportation because the pressurized metal tanks used for storing hydrogen gas for transportation are very expensive. 

A potentially more efficient method of storing hydrogen is in hydrides. Hydrides are chemical compounds of hydrogen and other materials. Research is currently being conducted on magnesium hydrides. Certain metal alloys such as magnesium nickel, magnesium copper, and iron titanium compounds, absorb hydrogen and release it when heated. Hydrides, however, store little energy per unit weight. Current research aims to produce a compound that will carry a significant amount of hydrogen with a high energy density, release the hydrogen as a fuel, react quickly, and be cost-effective. 

A company in Utah, Power Ball Technologies, has developed a process in which sodium metal is pelletized and encapsulated with polyethylene plastic. The pellets can then be containerized, transported, and then opened in a patented hydrogen generator to produce hydrogen gas. According to the company, each gallon of these pellets is capable of producing 1,307 gallons of hydrogen gas, which is an equivalent hydrogen storage density more than 7 times greater by volume than a compressed hydrogen tank storing hydrogen at 3,000 psi. 

The Cost of Hydrogen

Currently the most cost-effective way to produce hydrogen is steam reforming. According to the U.S. Department of Energy, in 1995 the cost was $7.39 per million Btu ($7.00 per gigajoule) in large plant production. This assumes a cost for natural gas of $2.43 per million Btu ($2.30 per gigajoule). This is the equivalent of $0.93 per gallon ($0.24 per liter) of gasoline. The production of hydrogen by electrolysis using hydroelectricity at off peak rates costs between $10.55 to $21.10 per million Btu ($10.00 to $20.00 per gigajoule). 

Hydrogen Research in the United States

Recognizing the potential for hydrogen fuel, the U.S. Department of Energy (DOE) and private organizations have funded research and development (R&D) programs for several years. DOE has a major effort to develop hydrogen as a major fuel within the next few decades.

What is "Fuel From Water?"

Fuel from water is the process of removing the 2 hydrogen molecules from the H2O so that the hydrogen may be used as "hydrogen fuel."

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