Fuel cells run on hydrogen, the simplest element and most plentiful gas in the universe. Hydrogen is a diatomic element, meaning that in its liquid and solid states, hydrogen naturally forms into pairs of atoms, which is why hydrogen is often referred to as “H2”. Hydrogen is the lightest element, yet it has the highest energy content per unit weight of all fuels. Hydrogen’s energy density is 52,000 Btu/lb., which is three times greater than that of gasoline.
In nature, hydrogen is never found on its own; it is always combined into molecules with other elements, typically oxygen and carbon. Hydrogen can be extracted from virtually any hydrogen-containing compound, including both renewable and non-renewable resources. Regardless of the fuel source, fuel cells utilize hydrogen with little to no polluting emissions, making hydrogen the ultimate clean energy carrier.
Hydrogen gas is similar to natural gas in that it is lighter than air, so it rises and disperses quickly. Hydrogen is non-toxic and safe to breathe. Hydrogen is also odorless, colorless, and tasteless; since it cannot be odorized like natural gas, hydrogen detection and ventilation systems are employed. Like all fuels, hydrogen is flammable and must be handled properly.
In the U.S., hydrogen is transported safely through 700 miles of pipelines, and 70 million gallons of liquid hydrogen is transported annually by truck over U.S. highways without incident. Both indoor and outdoor hydrogen refueling stations are located in several dozen states and have safely dispensed compressed hydrogen for use in passenger vehicles, buses, trucks, forklifts, and other types of vehicles.
Click on the resources below for more information on hydrogen safety.
Fuel Leak Simulation - Published by Dr. Michael R. Swain, University of Miami, this report compares the severity of a hydrogen and gasoline fuel leak and ignition. Images from the video are included.
Hydrogen and Fuel Cell Safety Report – A monthly electronic publication published by the Fuel Cell and Hydrogen Energy Association (FCHEA) which provides information about developing hydrogen and fuel cell Codes and Standards and related safety information.
Hydrogen and the Law: Safety and Liability – A Fuel Cells 2000 presentation with statistics and information on hydrogen safety.
Hydrogen Safety for First Responders – A web-based course from the Department of Energy that provides an “awareness level” overview of hydrogen for fire, law enforcement, emergency medical personnel, along with all other interested persons. This multimedia tutorial introduces hydrogen, its basic properties, and how it compares to other familiar fuels. Tutorial also covers hydrogen use in fuel cells for transportation and stationary power, potential hazards, initial protective actions, and supplemental resources.
Hydrogen can be produced from a wide range of feedstocks, and any hydrogen-rich material can serve as a possible fuel source for fuel cells. Hydrocarbon fuels, novel feedstocks such as landfill gas, anaerobic digester gas, and biomass can also produce hydrogen, as can compounds containing no carbon, such as ammonia or borohydride. The vast majority of today’s hydrogen is produced via steam reformation of natural gas (95% in the U.S., roughly 48% globally), but alternative sources such as biogas are growing in popularity.
Hydrocarbon fuels – methanol, ethanol, natural gas, petroleum distillates, liquid propane, and gasified coal – can yield hydrogen in a process called reforming. Natural gas, the feedstock of choice for most of today’s mass-produced hydrogen, contains methane (CH4) that can be used to produce hydrogen via a thermal process known as steam-methane reformation. In steam-methane reforming, methane reacts with steam in the presence of a catalyst to produce hydrogen, carbon monoxide, and a relatively small amount of carbon dioxide. Steam reforming is endothermic, meaning heat must be supplied to the process for the reaction to proceed. The process is approximately 72 percent efficient. This type of reforming works similarly for other hydrocarbon fuels, combining the fuel with steam by vaporizing them together at high temperatures. Hydrogen is then separated out using membranes. Another type of reformer is the partial oxidation (POX) reformer. Some CO2 is emitted in the reforming process, but the emissions of NOX, SOX, particulates, and other smog producing agents are cut to zero.
When an electric current is introduced to water (H2O), hydrogen and oxygen are separated, with hydrogen forming at the cathode and oxygen forming at the anode. Electricity can be provided from any source, but using solar and wind energy to electrolyze water provides the cleanest pathway to produce hydrogen. This model is being used in some hydrogen refueling stations and in renewable energy storage systems that utilize hydrogen.
Another method to generate hydrogen is with bacteria and algae. Cyanobacteria, an abundant single-celled organism, produce hydrogen through its normal metabolic function. Cyanobacteria can grow in the air or water, and contain enzymes that absorb sunlight for energy and split the molecules of water, thus producing hydrogen. Since cyanobacteria take water and synthesize it to hydrogen, the waste emitted is more water, which becomes food for the next metabolism. Sodium borohydride (NaBH4) is an inorganic compound that can dissolve in water in the absence of a base. Hydrogen can be generated through catalytic decomposition.
Storage & Delivery
Hydrogen can be stored as either a liquid or a gas. To store hydrogen in liquid form, hydrogen must be cooled to -423 °F, requiring a tremendous amount of energy. Therefore, hydrogen produced in large quantities is usually pressurized as a gas then stored in caverns, gas fields, or mines before being piped to the consumer as natural gas is today. Researchers are examining an impressive array of storage options with support from the U.S. Department of Energy.
Hydrogen vehicle fueling stations may generate hydrogen on-site or receive deliveries of trucked-in hydrogen. In either case, the stations possess equipment to compress, store and dispense the hydrogen fuel. Compressing hydrogen gas to 350 (5,000 psi) or 700 bar (10,000 psi) reduces the volume, and the compressed gas is then stored onsite in high pressure or cryogenic tanks. A few sites store hydrogen in liquid form, which is converted to a gaseous state and compressed before being dispensed. Researchers are also examining additional storage options, such as the use of advanced solid state materials and liquid materials.
On-board hydrogen storage is a challenge for automotive engineers, who are limited by size and weight constraints while seeking to meet the driving range of today’s gas-fueled vehicles (300 or more miles per fueling). Several recent fuel cell vehicles have either met or exceeded this milestone with novel tank design. Researchers are examining an array of storage options with support from the U.S. Department of Energy (DOE). Today’s fuel cell electric (FCEVs) use compressed hydrogen tanks or liquid hydrogen tanks. New technologies, such as metal hydrides and chemical hydrides may be come viable in the future. Another option is to store hydrogen-containing compounds, such as gasoline or methanol, onboard a vehicle and extracting the hydrogen using a fuel reformer.
Today, there are more than 100 hydrogen fueling stations operating around the world, with a fueling process that is swift (just minutes) and remarkably similar to filling up a tank with gasoline.
See our Charts section for more details on worldwide hydrogen fueling stations.