As soon as the durability and high material cost issues are resolved, mass production of these
kinds of eco-friendly cars seems within sight. Because they have virtually zero emissions, they appear to be preferable to HEV or PHEV vehicles.

Several types of fuel cells exist for a multitude of applications, but automobiles focus specifically on a Protonic Exchange Membrane (PEM) type. PEM fuel cells are ideal for this application because they run at lower temperatures (approximately 70º C) compared to other types such as solid oxide fuel cells, which run at 600 to 1000º C, and they have excellent power densities.

A PEM fuel cell consists of a stack of cells called an MEA (Membrane Electrode Assembly). The MEA sits between two separators, and several hundreds of cells are combined in a series to form a fuel cell stack to produce the required voltage. A single cell of this type generates less than one volt.

A fuel cell produces electricity through a reaction between hydrogen and oxygen, which takes place inside the MEA. The MEA consists of a polymer electrolyte membrane sandwiched between two catalysts. Hydrogen enters the anode catalyst and activates the hydrogen molecules to release electrons. As the electrons flow from the anode to the cathode catalyst, they produce an electrical current, which provides the required electricity. The hydrogen molecules that released the electrons migrate to the cathode; the oxygen enters the side with the cathode, bonds with the hydrogen molecules, and forms water. Water and heat are the only waste materials produced by a fuel cell.

Many of the engineering challenges that were directly associated with early fuel-cell vehicles have recently been overcome. Traditionally, fuel-cell cars stored a limited amount of hydrogen, which significantly affected mileage. In this way they could not compete with gasoline-powered vehicles. Most were limited to around 200 miles per tank of hydrogen. Now fuel-cell vehicles are available with cruising ranges of about 500 miles per tank. And another significant technological breakthrough has been the ability to start these vehicles in colder climates, in temperatures as low as -30º C, which competes with gasoline-powered engines.

But, some problems seem to persist. For instance, endurance over long distances still remains an issue, and so does the high cost of the materials used for manufacturing the cells, such as the platinum catalyst. In addition, the source hydrogen must be made initially using electricity, which, in turn, must come from coal, petroleum, or natural gas – and all of these emit CO2. Although a possible solution here might come from the most common method for attaining hydrogen, which is to split natural gas into positively and negatively charged ions using an electrolyzer, this process unfortunately releases CO2 as a byproduct. Many companies are researching and developing better carbon dioxide recovery systems; but, they are still in early testing stages and are expensive.

One more caveat: For a fuel-cell vehicle to be the ultimate eco-friendly car, it needs to exist in a pure hydrogen economy, where hydrogen is generated from renewable sources, such as wind and solar. But although extremely promising, this technology is relatively costly and still in its infancy. The nation’s energy infrastructure would have to be re-built, and the high cost of this would have to “offset human nature.” Fuel-cell vehicles might soon be available for all of us to enjoy, but how long will it take before everyone is confident enough to invest in them?

History tells us that such fundamental transitions take some time, and a mix of products will keep us “going green” until cars can completely “go green.” That’s probably why one leading auto manufacturer makes the following statement on its Website: “The fuel cell is one of the many technologies the company will continue to pursue.”

NASA
www.nasa.gov