Micro fuel cells are being touted as the hot portable energy source of the future. They pack a lot more punch than batteries and yield only water as a by-product. Yet the revolution in small power sources is not likely to occur until the second half of this decade, when developers expect to unveil miniaturized fuel cells for third-generation cellular phones, laptop computers, personal digital assistants and other portable electronics.
"Potential military and consumer users," reports Christopher Dyer, a fuel cell researcher and editor of the International Journal of Power Sources, "say they expect micro fuel cells to make inroads into markets now dominated by batteries within the next five years"--three years if key breakthroughs are made. As it stands today, prototype micro fuel cells still fall short of the mark.
Energy content is not the problem. In practice, a kilogram of hydrogen fuel can deliver from 1,000 to 23,000 watt-hours of energy, whereas the best lithium batteries now range from 175 to 300. But today's prototype micro fuel cells barely reach 100.
Although some developers are using hydrogen fuel stored chemically in canisters, most designers have opted for methanol, a cheap and widely available fuel. Breaking down methanol into hydrogen ions is chemically slow and thus limits power output. Platinum and ruthenium are typically employed to catalyze the reaction, but those elements are costly, so their use must be minimized, says Chao-Yang Wang, director of the Electrochemical Engine Center at Pennsylvania State University.
Other problems include fuel leakage through the membrane, excessive heat buildup, moisture retention, and corrosion of the PEM by methanol. To avoid PEM degradation, most designers dilute methanol in water (to less than 5 percent), thereby yielding less energy. Many are working to make PEMs more robust. Robert Hockaday of New York City-based Manhattan Scientifics, for example, reports that his group has proprietary techniques that enable its cells to use 50 percent methanol fuel concentrations.
Medis Technologies in Yehud, Israel, employs a liquid electrolyte, which avoids the PEM's drawbacks. It also relies on catalysts that incorporate extremely fine grained powders of electrically conductive polymers, thereby reducing the amount of expensive platinum-family metals needed. Medis has a deal with the Sagem Group (a French cell phone maker) and is building a pilot plant that can produce 50 million micro fuel cell units a year.
The Medis cell can also use ethanol for fuel--a useful feature for travelers.
Consequently, I could get a bottle of good "akpeteshie" from a kiosk, pour some into a fuel cartridge and place it in the fuel cell. Cheap akpeteshie would presumably work, too.
