Fuel Cells

In the late 1900s, a new type of electrochemical power device emerged that is believed by some scientists and engineers to hold promise as an alternative energy source: the fuel cell.

Hydrogen Fuel

The most talked-about fuel cell during the early years of research and development became known as the hydrogen fuel cell. As its name implies, it derives electricity from hydrogen. The hydrogen combines with oxygen (that is, it oxidizes) to form energy and water. There is no pollution, and there are no toxic by-products. When a hydrogen fuel cell “runs out of juice,” all that is needed is a new supply of hydrogen, because its oxygen is derived from the atmosphere.

Instead of combusting, the hydrogen in a fuel cell oxidizes in a more controlled fashion, and at a much lower temperature. There are several schemes for making this happen. The proton exchange membrane (PEM) fuel cell is one of the most widely used. A PEM hydrogen fuel cell generates approximately 0.7 V of dc. In order to obtain higher voltages, individual cells are connected in series. A series-connected set of fuel cells is technically a battery, but the term used more often is stack. Fuel-cell stacks are available in various sizes. A stack about the size and weight of an airline suit- case filled with books can power a subcompact electric car. Smaller cells, called micro fuel cells, can provide dc to run devices that have historically operated from conventional cells and batteries. These include portable radios, lanterns, and notebook computers.

Other Fuels

Hydrogen is not the only chemical that can be used to make a fuel cell. Almost anything that will combine with oxygen to form energy has been considered. Methanol, a form of alcohol, has the advantage of being easier to transport and store than hydrogen, because it exists as a liquid at room temperature. Propane is another chemical that has been used for powering fuel cells. This is the substance that is stored in liquid form in tanks for barbecue grills and some rural home heating systems. Methane, also known as natural gas, has been used as well. Some scientists and engineers object to the use of these fuels because they, especially propane and methane, closely resemble fuels that are already commonplace, and on which society has developed the sort of dependence that purists would like to get away from. In addition, they are derived from so-called fossil fuel sources, the supplies of which, however great they might be today, are nevertheless finite.

A Promising Technology

As of this writing (2006), fuel cells have not yet replaced conventional electrochemical cells and batteries. Cost is the main reason. Hydrogen is the most abundant and simplest chemical element in the universe, and it does not produce any toxic by-products. This would at first seem to make it the ideal choice for use in fuel cells. But storage and transport of hydrogen has proven to be difficult and expensive. This is especially true for fuel cells and stacks intended for systems that aren’t fixed to permanent pipelines.

An interesting scenario, suggested by one of my physics teachers all the way back in the 1970s, is the piping of hydrogen gas through the lines designed to carry methane. Some modification of existing lines would be required in order to safely handle hydrogen, which escapes through small cracks and openings more easily than methane. But hydrogen, if obtained at reasonable cost and in abundance, could be used to power large fuel-cell stacks in common ouseholds and businesses. The dc from such a stack could be converted to utility ac by power inverters similar to those used with PV energy systems. The entire home power system would be about the size of a gas furnace.