Hydrogen is an element consisting of one proton and an electron. It is the most abundant element in the universe but, it does not occur naturally as a gas in the Earth. It is always combined with other elements including hydrocarbons, water, and other organic substances. The efficient production of hydrogen from these substances is one of the challenges involved in using hydrogen as fuel.
Hydrogen is a non-polluting alternative fuel that can be produced using domestic resources. It is considered as an alternative transportation fuel due to its clean-burning properties, it has the potential to be produced domestically and with high efficiency of its fuel cell vehicle - it is two or three times efficient than a gasoline vehicle. The energy in 2.2 pounds of hydrogen gas is the same as that in one gallon of gasoline. As hydrogen has a low volumetric energy density, it is necessary to store sufficient fuel onboard in a fuel cell vehicle in order to have a driving range equivalent to that of conventional vehicles.
Some of the, currently available, hydrogen storage technologies include compressing gaseous hydrogen in high-pressure tanks and cryogenically cooling liquid hydrogen to -253°C (-423°F) in insulated tanks. Other technologies currently under research include chemically bonding hydrogen with metal hydride. Hydrogen fuel cells will likely be used in stationary power devices and portable devices followed by transportation applications. Most of the automobile manufacturers are analyzing the latest prototypes of hydrogen fuel cell vehicles. Fuel cells are a viable technology offering significant economic, environmental, and energy efficiency benefits. However, there exist a number of barriers to their use in vehicles like high capital costs, lack of hydrogen distribution infrastructure, and challenges related to hydrogen storage.
Hydrogen Fuel Cells
Hydrogen fuel cells directly convert the chemical energy in hydrogen to electricity and release water and useful heat as by-products. Hydrogen fuel cells are pollution-free and have greater efficiency than traditional combustion technology.
The operation of the hydrogen fuel cells is similar to that of a battery. The hydrogen fuel cell has two electrodes - an anode and a cathode, which are separated by a membrane. Oxygen passes over the cathode, and hydrogen passes over the anode. The hydrogen reacts with a catalyst on the anode which converts hydrogen into positively charged ions (H+) and negatively charged electrons (e-). The electrons flowing out of the cell are used as electrical energy to power an electric motor. The hydrogen ions then pass through the membrane to the cathode and combine with oxygen and the electrons to yield water.
The power produced by a fuel cell is based on certain parameters like temperature, size, and type of the fuel cell, and the pressure at which the gases are supplied. A single fuel cell is capable of producing enough voltage for the smallest applications. Individual fuel cells are combined to form a stack in order to increase the voltage. However, a fuel cell stack may contain several individual cells that are layered together depending on the application. This scalability renders fuel cells ideal for several applications.
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Advantages and Disadvantages
The key benefits of hydrogen fuel cells include the following:
- Unlike gasoline- and diesel-powered vehicles, hydrogen fuel cells do not produce air pollutants. It only produces nitrogen oxides when burned in engines.
- It reduces dependence on petroleum imports as hydrogen can be domestically produced from various sources.
- Fuel cell vehicles powered by hydrogen do not produce greenhouse gas emissions.
The following are some of the disadvantages of hydrogen fuel cells:
- Hydrogen fuel cell vehicles are currently very expensive than conventional vehicles or any hybrids.
- Fuel cell vehicles are not as durable as internal combustion engines in terms of temperature and humidity ranges.
- The availability of hydrogen is limited to certain locations and hydrogen is quite expensive to produce as well.
- Hydrogen fuel cell vehicles produce very little energy when compared to other gasoline or diesel vehicles and hence it is difficult to achieve a high driving range.
- The systems used for delivering gasoline from refineries to gasoline stations cannot be used for hydrogen.
Uses of Hydrogen Fuel Cells
The following are some of the applications of hydrogen fuel cells:
- NASA is the primary user of hydrogen resources for its space program. NASA fuels the booster rockets of the space shuttle using liquid hydrogen and employs hydrogen batteries for electrical sources.
- Hydrogen fuel cells can power any portable device that uses batteries. Unlike a typical battery, the hydrogen fuel cell continues to produce energy with a continuous supply of fuel. This ability of the fuel cells enables them to power devices like hearing aids, video recorders, cellular phones, and laptop computers.
- Stationary hydrogen fuel cells are the largest and most powerful fuel cells. They are a clean, reliable source of power to cities, towns, and buildings. These fuel cells are also used for back-up and remote power applications including remote weather stations and rural locations.
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Sources and Further Reading