The use of hydrogen as a transportation energy source in the U.S. could help to address growing concerns of energy security, global climate change, and air quality.
Hydrogen is one of the cleanest fuels available for transportation. Hydrogen does not produce carbon monoxide (CO), carbon dioxide (CO2), or hydrocarbon (HC) emissions because it does not contain carbon. The main byproduct of its use is water (H2O).
Unlike fossil fuels, which will eventually run out, hydrogen is a renewable energy source that is almost unlimited. However, there will always be the need for a source of energy to produce hydrogen gas for use in vehicles.
There are two main categories of hydrogen-powered vehicles, those that use internal combustion engines (ICEs) and those that use fuel cells to produce power. Similar to conventional vehicles powered by ICEs, hydrogen-powered vehicles have an internal combustion engine (ICE) that intakes air and hydrogen. The fuel air charge is ignited with a spark as is done in gasoline engines.
Hydrogen gas can also be used as a fuel source for a fuel cell—a device that creates an electrical current to power a vehicle. Vehicles that are powered with hydrogen fuel cells do not have onboard internal combustion engines and are significantly different from conventional ICE powered vehicles.
A hydrogen fuel cell can be used in a hydrogen-fueled powertrain. The fuel cell converts a fuel’s chemical energy to electrical energy by reacting with oxygen or an oxidizing agent. The electrical energy can be used to drive an
Hydrogen fuel cells are attractive to vehicle manufacturers because they produce no toxic emissions and do not have the operating range limitations of electric vehicles. Some prototype hydrogen fuel cell vehicles can drive more than three hundred miles on a single fill.
A hydrogen fuel cell uses a device called a proton exchange membrane (PEM) to separate hydrogen protons from hydrogen electrons. The hydrogen protons are forced through a membrane, through which hydrogen electrons
cannot pass. The electrons travel along an external path, creating an electrical current, before rejoining the protons. The hydrogen molecules then combine with oxygen to form water, which leaves the vehicle through the powertrain’s
The fuel cell produces direct current, which is then inverted to AC by an inverter. The inverter powers an AC electric motor to propel the vehicle. The inverter, the electric motor, and the vehicle’s DC-DC converter, which supplies power to
12V circuits, are all similar to such components, as found in hybrid and electric vehicles.
U.S. Department of Energy Alternative Fuels Data Center, “Hydrogen Fuel Cell Vehicle”, in “How Do Fuel Cell Electric Vehicles Work Using Hydrogen?”. https://afdc.energy.gov/vehicles/how-do-fuel-cell-electric-cars-work.
A hydrogen fuel cell requires an air compressor to provide a steady supply of oxygen to the fuel cell’s cathode. The air must be filtered so that contaminants do not damage the fuel cell. Hydrogen sensors are typically mounted at various
places around the vehicle, including the passenger compartment, to monitor the system for any leaks that may occur.
Hydrogen is the lightest element, and like most other gaseous fuels, must be compressed to high pressures to fit into in a fuel tank that is small enough for a powertrain. The most common hydrogen storage pressure today is 10,000
psi, although some vehicles have used lower tank pressures. The cylindrical tanks are typically made of aluminum or stainless steel, which is then wrapped in carbon fiber for added strength. As with all pressurized tanks for gaseousfueled
vehicles, hydrogen fuel tanks must be periodically inspected. Some vehicle manufacturers have experimented with cryogenic hydrogen fuel storage in which the fuel is stored at extremely low temperatures. At approximately –455º F or (–260º C), hydrogen becomes liquid and takes up less space than hydrogen gas. However, liquefying hydrogen consumes a significant amount of energy, and once liquefied, the hydrogen must be stored in an extremely well-insulated tank.
Interest in hydrogen as a renewable fuel source is growing rapidly around the globe. Major auto manufacturers are creating prototype models that are making hydrogen fuel a practical replacement for fossil fuels. Hydrogen has great promise for transportation applications. However, hydrogen-powered vehicles are not widely offered to the general public at this time. It has been estimated that it will take approximately ten to twenty years before hydrogen vehicles and the infrastructure needed to support them will begin to make an impact.
Though hydrogen-powered vehicles hold great promise, the production of hydrogen as a fuel continues to present significant challenges. It will be some time before people across the United States can purchase hydrogen ICE or fuel cell vehicles. Only time will tell what the future holds for hydrogen-fueled vehicles.