Hydrogen Basics
What is hydrogen?
Source: NASA (public domain)
Did you know?
Hydrogen is the lightest element. Hydrogen is a gas at normal temperature and pressure, but hydrogen condenses to a liquid at -423° Fahrenheit
(-253° Celsius).
Hydrogen is the simplest element. Each atom of hydrogen has only one proton. Hydrogen is also the most plentiful gas in the universe. Stars like the sun consist primarily of hydrogen.
The sun is essentially a giant ball of hydrogen and helium gases. In the sun's core, hydrogen atoms combine to form helium atoms. This process—called fusion—gives off radiant energy.
The radiant energy from the sun gives earth light and helps plants grow. Radiant energy is stored as chemical energy in fossil fuels. Most of the energy that people use today originally came from the sun's radiant energy.
Hydrogen as a gas (H2) is not found by itself on earth. Hydrogen gas is found only in compound form with other elements. Hydrogen combined with oxygen is water (H2O). Hydrogen combined with carbon forms different compounds like methane (CH4), coal, and petroleum. Hydrogen is found in all growing things and is an abundant element in the earth's crust.
Hydrogen has the highest energy content of any common fuel by weight (about three times more than gasoline), but it has the lowest energy content by volume (about four times less than gasoline).
Hydrogen is an energy carrier
Energy carriers move energy in a useable form from one place to another. Electricity is the most well-known energy carrier. Hydrogen is an energy carrier like electricity, and it must be produced from another substance. Hydrogen can be produced from a variety of sources—water, fossil fuels, or biomass—and it is a byproduct of other chemical processes. Hydrogen is not widely used as a fuel now, but it has the potential for greater use in the future.
How is hydrogen produced?
Source: U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Hydrogen Production (public domain)
To use hydrogen for energy, it must be separated from the other elements in the molecules where it occurs. Hydrogen atoms can be separated from water, hydrocarbons, and biomass.
The two most common methods for producing hydrogen are steam reforming and electrolysis (water splitting).
Steam reforming is a widely used method of hydrogen production
Steam reforming is currently the least expensive way to produce hydrogen, and it accounts for most of the commercially produced hydrogen in the United States. This method is used in industries to separate hydrogen atoms from carbon atoms in methane (CH4). The steam reforming process results in carbon dioxide emissions.
Electrolysis uses electricity
Electrolysis is a process that splits hydrogen from water using an electric current. The process can be used on a large or small scale. Electrolysis does not produce any emissions other than hydrogen and oxygen, and the electricity used in electrolysis can come from renewable sources such as wind or solar energy. If the electricity used in electrolysis is produced from fossil fuels, then pollution and carbon dioxide emissions are indirectly associated with electrolysis.
Other methods of producing hydrogen
Research is underway to develop other ways to produce hydrogen. These methods include using microbes that use light to make hydrogen, converting biomass into liquids and separating the hydrogen, and using solar energy technologies to split hydrogen from water molecules.
Source: National Aeronautics and Space Administration (NASA) (public domain)
Source: Adapted from the National Energy Education Project (public domain)
Source: Wikimedia Commons
Use of hydrogen
Nearly all of the hydrogen consumed in the United States is used by industry for refining petroleum, treating metals, producing fertilizer, and processing foods.
Rocket fuel is the main use of hydrogen for energy
The National Aeronautics and Space Administration (NASA) is the largest user of hydrogen as a fuel. NASA began using liquid hydrogen in the 1950s as a rocket fuel, and NASA was one of the first to use fuel cells to power the electrical systems on space craft.
Hydrogen fuel cells produce electricity
Hydrogen fuel cells produce electricity by combining hydrogen and oxygen atoms. This combination results in an electrical current. A fuel cell is two to three times more efficient than an internal combustion engine running on gasoline.
Many different types of fuel cells are available for a wide range of applications. Small fuel cells can power laptop computers, cell phones, and military applications. Large fuel cells can provide electricity for emergency power in buildings and in remote areas that do not have power lines. Hydrogen use in vehicles is a major focus of fuel cell research and development.
Hydrogen use in vehicles
The interest in hydrogen as an alternative transportation fuel is based on hydrogen's ability to power fuel cells in zero-emission electric vehicles, its potential for domestic production, and the fuel cell vehicle's potential for high efficiency.
In the United States, about 500 hydrogen-fueled vehicles are in use, and about 330 of those are registered in California. Most hydrogen-fueled vehicles are automobiles and transit buses that have an electric motor powered by a fuel cell. A few of these vehicles burn hydrogen directly. The high cost of fuel cells and the limited availability of hydrogen fueling stations have limited the number of hydrogen-fueled vehicles.
The refueling challenge
Production of hydrogen cars is limited because people won't buy hydrogen cars if refueling stations are not easily accessible, and companies won't build refueling stations if they don't have customers with hydrogen-fueled vehicles. In the United States, about 55 hydrogen refueling stations for vehicles are operating. About 30 of these stations are available for public use, nearly all of which are located in California. The California Energy Commission has a program to help fund the development of publicly accessible hydrogen refueling stations throughout California to promote a consumer market for zero-emission fuel cell vehicles.