Hydrogen is making a name for itself as part of the nation’s alternative fuel portfolio. But how much do you know about this alternative fuel? The element, the simplest on Earth, is certainly nothing new. What are new are the continually developing technologies that have helped to develop it for use as a replacement for fossil fuels. A hydrogen atom consists of only one proton and one electron. It is also the most plentiful element found in the universe.
But just because this simple element is found in endless supplies doesn’t mean it occurs naturally as a gas on Earth. Instead, it is always combined with other elements. For example, you probably know that water is actually a combination of hydrogen and oxygen. But that isn’t the only place hydrogen is found. The element, often in the form of hydrocarbons, is found in many compounds that are subsequently used as gasoline, propane, methanol, and natural gas.
For a fuel cell to generate electricity using hydrogen, the pure hydrogen must first be extracted from a hydrogen-containing compound.
Fuel cells are one of the more exciting energy technologies, not only for fueling vehicles but also for heating and powering buildings. They may appear to act like batteries, but they come with one huge difference: they don’t run down. Since they don’t run down, they also do not need recharging. Fuel cells can continue to produce electricity and heat as long as they are receiving fuel.
Fuel cells contain two electrodes, much like a battery, one negative and one positive, surrounded by an electrolyte. The source fuel, such as hydrogen, is then fed to the anode, or negative electrode, while air is streamed into the cathode, or positive electrode. Electrons go through an external circuit, which creates a flow of electricity. Meanwhile, protons move through the fuel cell’s electrolyte on their path to the cathode. Once there, they reunite with oxygen as well as the electrons to yield water and heat.
Several types of fuel cells have been developed. Below are some of the more common:
Polymer electrolyte membrane fuel cells. If you have heard about fuel cell use in vehicles, you are probably familiar with polymer electrolyte membrane fuel cells. These cells, also known as PEM fuel cells, probably hold the most promise to date for use in powering personal vehicles. These fuel cells actually use a polymer membrane in place of the electrolyte. They are able to operate at fairly low temperatures. These fuel cells are able to alter their output to meet changing demands for power. In addition to their potential use in vehicles, PEM fuel cells also hold potential for power generation while stationary.
Regenerative fuel cells. This is a special class of fuel cells, and like other fuel cells, regenerative fuel cells create electricity from hydrogen and oxygen. But they differ from other fuel cells in one important way: the process can be reversed and the fuel cell powered with electricity to produce hydrogen and oxygen. Why is this important? Some day, the technology of these fuel cells could provide storage of excess energy that is produced by varying sources of renewable energy, be it wind or solar or some other source. During times of lower power production, the energy can then be released.
Direct-methanol fuel cell. These fuel cells are similar to the more common PEM cell, using a polymer membrane as the electrolyte. But unlike the PEM cell, these fuel cells use methanol directly on the anode, eliminating any need for a fuel reformer. These fuel cells are beginning to garner more attention.
Phosphoric Acid Fuel Cells. Used most often in modules of 400 kW or more, these fuel cells are often tapped for use in generating power for places like hotels, hospitals, stores and commercial buildings, and often contain systems that allow for the use of waste heat. Phosphoric acid fuel cells use a phosphoric acid electrolyte held inside a porous matrix, operating at around 200 degrees C. Phosphoric acid is sometimes immobilized in polymer membranes, allowing for use in a number of stationary power application situations.