Hydrogen Key Terms
May 20, 2014
What are the key terms to know when discussing hydrogen fuel, fuel cell vehicles, and hydrogen fueling infrastructure?
It is important to know how to "talk the talk" when it comes to hydrogen and hydrogen-fueled vehicles. Becoming familiar with the terms below will help you better understand the fuel so you can ask the right questions and make informed decisions.
Considered an alternative fuel under the Energy Policy Act of 1992 (EPAct), hydrogen (H2) can dramatically reduce emissions and has the potential to significantly reduce our dependence on imported petroleum. While pure hydrogen is not abundant, it is present in water (H2O), hydrocarbons (e.g., methane, CH4), and other organic matter.
Although hydrogen is not currently widely used as a transportation fuel, government and industry are developing clean, economical, and safe hydrogen fuel and hydrogen-fueled vehicles. The first commercially available hydrogen vehicle is expected to be offered in select dealerships this year.
Fuel cell electric vehicles (FCEVs) are zero emission vehicles fueled by pure hydrogen gas stored directly in the vehicle. FCEVs are two to three times more efficient than a conventional vehicle powered by an internal combustion engine. FCEVs produce no harmful tailpipe emissions, have the ability to refuel in as little as three minutes, can achieve a range of more than 300 miles on a single fill-up, and may use other advanced efficiency technologies, such as regenerative braking systems.
Similar to battery electric vehicles, FCEVs use electricity to power a motor located near the vehicle's wheels. However, unlike other electric vehicles, FCEVs produce electricity from hydrogen using the fuel cell, leaving heat and water as byproducts. A fuel cell is a device that can convert the chemical energy of hydrogen into an electrical current through a chemical reaction with an oxidizing agent, such as oxygen. The most common type of fuel cell for vehicle applications is the polymer electrolyte membrane (PEM). A PEM fuel cell is composed of an electrolyte membrane positioned between a cathode (positive electrode) and an anode (negative electrode). The hydrogen gas is introduced to the anode, while oxygen is introduced to the cathode. A catalyst (typically platinum) induces an electrochemical reaction that splits the hydrogen molecule into hydrogen ions. The protons are allowed to pass through the membrane while the electrons are forced to travel through an external circuit to produce electricity for the car. Then the electrons combine with the protons and oxygen at the cathode to form water, which is the fuel cell's exhaust.
The energy in 2.2 pounds (1 kilogram) of hydrogen gas provides about the same FCEV driving range as a conventional sedan propelled on 1 gallon on gasoline. Due to hydrogen's low energy content by volume, the fuel must be stored as a gas in the fuel tank at high pressures (10,000 pounds per square inch). Additional research is currently underway to optimize fuel storage.
At this time, FCEVs are more expensive than conventional vehicles, but are nearing commercial readiness. Many major original equipment manufacturers, including Honda, Hyundai, and Toyota, have announced plans to begin selling or leasing FCEVs to the public in 2014 and 2015 in certain markets.
Hydrogen can be produced domestically from a variety of sources, such as natural gas, coal, and renewable resources (solar, wind, and biomass). The environmental impact and energy efficiency of hydrogen depends on how it is produced. A challenge of using hydrogen is efficiently and inexpensively producing hydrogen fuel.
Hydrogen for use in FCEVs is split from other molecules through either reforming (using steam) or electrolysis (using electricity and water). Currently, natural gas reforming is the cheapest and most efficient process to produce hydrogen in the United States.
If the hydrogen is produced through electrolysis from clean, renewable energy, FCEVs could produce zero lifecycle greenhouse gas emissions. There are projects underway to decrease the costs associated with these production methods.
Hydrogen stations are typically located in areas of current or expected FCEV deployment, and can either be designed to store delivered hydrogen, or to produce hydrogen on-site (via electrolosys or reforming). Fueling sites include storage tanks, compression, and fuel dispensing equipment. Hydrogen fueling stations can be standalone operations or co-located with conventional fuel or natural gas dispensers. Applicable safety standards and codes specific to hydrogen fuel include the National Fire Protection Agency (NFPA)'s NFPA 2: Hydrogen Technologies Code.
To date, most existing hydrogen fueling stations have been constructed as part of demonstration projects. Earlier this month, the California Energy Commission (CEC) awarded nearly $47 million in grants for the development of a network of retail hydrogen fueling stations throughout the state. As the FCEV market expands, fueling infrastructure is expected to continue to grow to meet the demand.
For more information on hydrogen fuel, vehicles, and infrastructure, you can visit the Alternative Fuels Data Center Hydrogen page and the U.S. Department of Energy (DOE)'s Hydrogen and Fuel Cells Program page.
- Clean Cities Technical Response Service Team