Are Cars Powered by Hydrogen Bad for the Environment?
One of the proposals to combat climate change is to power cars with hydrogen, which emits no air pollutants or carbon dioxide, the primary cause of global warming. It takes a lot of electricity to produce the hydrogen, so carbon dioxide and other air pollutants are emitted in the process. Considerable work is needed to make the technology available for the market and there is some debate about whether the environmental impacts justify the effort.
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History
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Scientists have been researching how to power vehicles with hydrogen for about 30 years. Many cars powered by hydrogen have been manufactured by the major automakers, and they are working to improve the technology. Some of the vehicles are hybrids; using both hydrogen fuel cells and electricity. There are many test cars and buses on the road, but the cars are not yet sold commercially.
How Fuel Cells Work
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When electric current is applied to water, it produces hydrogen and oxygen. Fuel cells reverse this process as compressed hydrogen and water are combined to produce electricity. The only waste product is water vapor (H20).
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Sources of Hydrogen
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Most hydrogen is produced from fossil fuels in a process called reforming, where a catalyst and steam are applied to form a chemical reaction. Reforming can be used with liquid or gaseous hydrocarbon fuels such as natural gas, gasoline, ethanol and methanol. Most of the hydrogen in the United States is produced from natural gas.
Hydrogen also may be obtained by gasification of coal or other carbon feedstocks such as biomass and municipal waste. High-pressure steam is applied to cause a chemical reaction that releases the hydrogen and pollutant byproducts such as carbon dioxide and sulfur can be captured.
Energy Efficiency
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The extent to which hydrogen cars are better or worse for the environment than other cars depends on the energy efficiency of the entire system. From producing and transporting the fuel, to operating the vehicles (called well-to-wheel efficiency). The higher the efficiency, the less energy is used in the process, and so the emissions are lower. The efficiency of producing and delivering the hydrogen to the vehicles is 60 percent, compared with 80 percent efficiency for gasoline. On the other hand, fuel cell vehicles are two to three times more energy-efficient than gasoline-powered vehicles.
Automakers are doing research on how to produce vehicles that are more energy-efficient. Toyota did a comparison of the energy efficiency of several types of vehicles. They found 40 percent well-to-wheel efficiency of a fuel-cell hybrid vehicle where the hydrogen was produced from natural gas. That compares with 34 percent efficiency for a Prius-like hybrid; 33 percent for an electric vehicle, with gas-fired power producing the electricity; and 19 percent for a gas-powered conventional vehicle.
Solutions
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One solution is to generate the electricity to produce the hydrogen with renewable resources, such as wind, solar, hydropower, geothermal and biomass.
Another solution is to obtain hydrogen in other ways. Research is being conducted on various techniques such as electrolysis, applying electricity to water to remove the hydrogen; capture from sewage water or municipal waste; thermal processing of biomass or agricultural waste; and using microorganisms to break down biomass.
Hydrogen Cars' Future
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Hydrogen fuel cell vehicles are not the environmental panacea that they were once hoped to be, but research continues on the technology to reduce the environmental impacts.
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