Beyond the day when electronics come with built-in fuel cells instead of batteries, another technology frontier looms: building fuel cells directly on chips. Already, Savinell’s group at Case Western has built a prototype only 1.5 centimeters by two centimeters. His group used microfabrication techniques to “print” five to six layers of fuel cell components-the membrane, electrode and catalyst-on ceramic and silicon wafers, and more recently on a flexible polymer material. At this scale, he’s using hydrogen as a fuel, stored as sodium borohydride and released with a platinum catalyst. “The hope is to provide power on a chip with a sensor and a transmitter-a totally self-sufficient device,” Savinell says.
Researchers at the Georgia Institute of Technology, MIT, Stanford University and Sandia National Laboratories in Livermore, CA, are also working on building chip-scale fuel cells. To make these devices run on easily stored methanol, Paul A. Kohl, a professor of chemical engineering at Georgia Tech, is fabricating tiny channels on silicon through which methanol and water can pass. These channels could be created on a conventional silicon-chip assembly line. “You could design the fuel cell to supply exactly the power you want and be the size you want,” says Kohl.
Beyond shrinking fuel cells to the chip scale, another long-term goal is enabling fuel cells to directly tap the power of hydrogen but avoid high-pressure tanks. One ambitious approach would make use of carbon nanotubes: pipelike carbon molecules that have the ability to store and release hydrogen. Researchers envision nano canisters full of hydrogen that could keep fuel cells humming, but this will require breakthroughs in materials and manufacturing methods, says Michael Heben, leader of a nanostructured-materials group at the U.S. Department of Energy’s National Renewable Energy Laboratory in Golden, CO. “It could be that someone puts their finger on this in the next week, or it could take 20 years,” he says.
The most credible, reproducible results to date, says David Tomanek, professor of physics at Michigan State University, were achieved by Mildred Dresselhaus, a physicist at MIT, and colleagues at the Chinese Academy of Sciences who reported finding a way for carbon nanotubes to store 4.2 percent of their weight in hydrogen. That may be enough for micro fuel cells, Tomanek says. “It will be lighter, smaller and safer than a tank, even at four percent, and this could be done in a couple of years. But I am an optimist,” he says. Dresselhaus herself is more guarded: “At the moment, we don’t have the magic wand. We have an opening that says, This is something to look for.’ The next step is still missing.” That next step could come within this decade, she adds, but “we need to have a major breakthrough.”
Other electronics giants are also experimenting with carbon molecules to improve micro fuel cells. NEC has reported using horn-shaped molecules known as carbon nanohorns as a substrate for platinum catalysts, providing more surface area for stronger chemical reactions and more power. And Sony says it is using soccer-ball-shaped carbon molecules known as fullerenes-the base components of carbon nanotubes-to construct better electrolytes.
Meanwhile, the first micro fuel cells are rapidly nearing the market. Of course, the prototypes need continual fine-tuning to make sure fuel can’t leak and to increase their efficiency. But these hurdles are relatively minor, industry watchers say. After all, batteries had their share of development troubles, too. The first high-energy lithium batteries tended to catch fire and even explode. As any cell-phone owner knows, those problems were solved.
There are plenty of reasons-about $6 billion worth, in fact-to suggest the same will happen with micro fuel cells, putting these remarkable tiny power packs in millions of consumers’ pockets. Indeed, as micro fuel cells emerge from cluttered labs like the Los Alamos outpost of Manhattan Scientifics, they may put batteries, with their limited power and heavy-metal waste disposal headaches, into technology’s recycle bin.