One of the promising "future fuels" is hydrogen. Although hydrogen is already used as fuel in vehicles like cars, buses, and rockets, it still is not feasible to have it propagated to the masses. Hydrogen powered cars are now available but only for fleet lease and commercial vehicles.
Hydrogen shares the same principle as fossil fuel in terms of being used as fuel. Hydrogen is still burned in the combustion chamber that will eventually convert it to mechanical energy. In fuel cells, hydrogen is reacted with oxygen to produce electricity (with a by-product of water) that will power an electric motor. Also they are considered as zero-emission vehicles.
Hydrogen powered cars are slowly gaining popularity in industrialized nations. With the government's heavy subsidies, people are slowly flocking to the hydrogen fuel cell cars. Many car manufacturers have a hydrogen car in their model line-up. But they are mostly prototype or leased to private corporations. But in June 2008, Honda unveiled the first commercial hydrogen fuel cell car, the FCX Clarity. It plans to produce 200 cars in the next three years. This is initially available in California because of the hydrogen infrastructure existing there.
The integral part of the FCX Clarity is the fuel cell. Simply put a fuel cell converts chemical energy into electrical energy. A fuel cells output is DC voltage which will then power an electric motor. The type of fuel cell depends on the electrolytes that it will use. Also there are types for stationary or mobile-portable use. A fuel cell will convert energy more efficiently than gasoline engine. According to some calculations, if hydrogen is used as primary chemical in fuel cell, it could convert 80% of hydrogen into electricity. Converting this electricity into mechanical energy uses an inverter; a reasonable efficiency ratio for this is around 80%. Getting the overall efficiency we will get around 64% comparing to a gasoline engine with and efficiency ratio of around 20%
So why are hydrogen power not coming online as fast as we expect? First is the problem of producing hydrogen itself. The economics of producing it is not yet feasible for mass production. In fact, hydrogen production could contribute to emission of more greenhouse gases because of the fossil fuel used to in its process. It will be more prudent if we could make hydrogen using alternative fuels like solar, wind, or nuclear power. Hydrogen infrastructure to support a big mass base is still not yet developed. Either you have more hydrogen filling station or bring an insanely big tank of hydrogen whenever you travel. Another problem is the storage issue of hydrogen. As this is a very volatile gas greater care must be practiced in handling it.
Fuel cell cost is also a big issue right now. The components that make up this fuel cells are very costly specially the rare metals that are used in it. Currently a PEMFC (a common type of fuel cell membrane) generation cost is at $110 per kilowatt, compared to the $35 per kilowatt for gas powered cars.
But hydrogen is still a great and promising alternative fuel. If developments will continue to move along we could expect a hydrogen-car filled future.