Using hydrogen as a transportation fuel is garnering more attention as new technologies to harness hydrogen's energy are developed, existing technologies are becoming more economically feasible, and vehicle manufacturers work to develop fuel cell vehicles with the same range as a gasoline-powered vehicle.
Hydrogen is a colorless, highly flammable gaseous fuel. It is the simplest and most abundant element on earth but is rarely found alone in nature. Instead, it is mostly bonded with other elements, forming water, methane, natural gas, and other organic sources. Hydrogen needs to be separated from these compounds to be used as a fuel.
Hydrogen can be separated from fossil fuels, nuclear energy, biomass, or water.
- Natural gas and methanol, coal, and biomass in their gaseous states are also sources for hydrogen. The hydrogen is captured through gas synthesis using steam reformers.
- Electrolysis uses electrical energy to split water molecules into hydrogen and oxygen.
Efficiently producing hydrogen from hydrocarbons is one of the greatest challenges to using hydrogen as a fuel. Producing hydrogen from renewable feedstocks or renewable energy (such as hydropower) and using it in fuel cell vehicles would be the most sustainable approach to using hydrogen.
Hydrogen is expensive to manufacture, resulting in costs of $3 to $4 dollars per gallon. Though using hydrogen in a fuel cell vehicle results in zero exhaust emissions, energy sources used to manufacture hydrogen include electricity or natural gas.
Hydrogen is a gas at normal temperatures and pressure, which presents greater transportation and storage hurdles compared to liquid fuels. Hydrogen can be transported to service stations as a gas or liquid. Because the majority of hydrogen is produced very close to where it is used, a safe hydrogen fuel infrastructure still needs to be developed.
Hydrogen can be compressed or liquefied and stored in tanks, or it can be stored by absorption on the surface of solids. Both compressed and liquid hydrogen have less energy content than what is found in the same quantity of gasoline. One pound of hydrogen has 44.4% the energy content than one gallon of gasoline. A light-duty fuel cell vehicle must store 11-29 pounds of hydrogen to achieve a driving range of at least 300 miles. With existing technologies, a tank larger than the trunk of a typical car would be needed to store this amount of hydrogen. To learn more about the fuel properties of hydrogen, visit
www.eere.energy.gov/afdc/fuels/properties.html.
Currently, there are only about 30 hydrogen stations in the United States. Most are in California and not available to the public.
Hydrogen vehicles have a limited range and are better suited for city driving, especially for commercial vehicles and delivery trucks.
Engine manufacturers have developed prototype hydrogen internal combustion engines (HICE), which can operate on either compressed or liquid hydrogen using a slightly modified internal combustion engine. The resulting emissions are mostly water and NOx because there is still a high temperature combustion process. The greatest potential for hydrogen is by using fuel cell vehicles.
Fuel cell vehicles reduce greenhouse gas emissions and emit no local pollution. They only emit oxygen-depleted air and residue water vapor. Fuel cell vehicles operate silently and with no vibrations like internal combustion engines, but are currently not commercially available to consumers.
These vehicles are similar to battery electric vehicles in that they are propelled by an electric motor; however, fuel cell vehicles create their own electricity instead of needing an external source to supply the electricity that is stored in the battery.
A hydrogen fuel cell is an electrochemical engine that generates electricity by converting the chemical energy of a fuel (hydrogen) and an oxidant (oxygen). In a hydrogen fuel cell reactor, hydrogen molecules are broken down to protons and electrons. Protons flow through a membrane and react with oxygen from the air to form water and heat. This reaction takes place inside a cell. Each cell comprises 2 electrodes, the anode and the cathode. The electrons flow from the anode to the cathode to create electricity. As long as pure hydrogen and a source of oxygen are supplied to the fuel cell, it will produce electrical energy.
Fuel cells can operate at efficiencies two to three times that of the internal combustion engine, require no moving parts, produce only heat and water, and are fuel-flexible.
Benefits of hydrogen include:
- Can be produced domestically from several sources
- Has the potential to reduce our dependence on foreign oil imports
- Produces no local air pollutants or greenhouse gases when used in fuel cells
- Emits only NOx when burned in internal combustion engines
- Is an abundant element
Challenges of hydrogen include:
- Production is too expensive to allow hydrogen to compete cost-wise with gasoline and diesel
- Takes energy to separate hydrogen from the compounds it bonded with, such as carbon or water
- Available only in a handful of locations, mostly in California
- Fuel cell vehicles are still expensive and too costly for most consumers
- Developing the hydrogen supply, transport, and storage infrastructure
- Energy content is less than gasoline or diesel on a per-volume basis, requiring bigger onboard hydrogen storage
