Fuel cells have been hailed as energy saviors in everything from hydrogen-powered cars to laptops. But these devices, which resemble batteries in that they generate electricity electrochemically but differ in requiring an outside fuel supply, have struggled to find more than niche roles. A key reason is cost.
When the choice is battery vs. fuel cell, says MIT’s Paula Hammond, “batteries almost always win because fuel cells are expensive.”
Hammond’s trying to help change that equation. In fact, she’s envisioning fuel cells that are not only cheaper than today’s devices but also flexible enough to be incorporated into, say, the wall of a tent, or even to be essentially shrink-wrapped around a laptop.
One key to such advances is a feature common to many types of fuel cells. Called the proton exchange membrane (PEM), it’s a gatekeeper, penetrable by protons — positively charged particles normally found in the nucleus of atoms — but not electrons. The latter are forced through an external circuit, in the process yielding the cell’s electric output.
But the most popular type of PEM, while successful, has issues: it’s costly, for example, and fails in low-humidity conditions. (Since the material must remain water-soaked, explains Hammond, a professor of chemical engineering, “it needs to be in at least 80 percent relative humidity.”) This means most fuel cells using the membrane need complicated casings that have to draw off some of the cell’s power to work right.
“If you had something that didn’t need that type of packaging,” notes Hammond, “it would be a lot easier to use in portable devices.” Thanks to a remarkable process called layer-by-layer (LBL) assembly, Hammond’s group is on the way to creating that new type of fuel cell.
LBL assembly relies on electrical charges or hydrogen bonding to form very thin, intimately bonded layers of different polymers, including some well-suited to fuel cell applications. Using LBL, Hammond’s group has already deployed selected polymers to make a very thin and flexible proton exchange membrane.
In early tests, fuel cells using the new-style PEMs produced about half as much energy per unit volume as their conventional counterparts, which was much better than expected. Importantly, says Hammond, “our fuel cell was actually operating at 60 percent humidity” — in other words, it can work in a wider range of conditions than could an unprotected conventional system.
The approach is due further refinement. Hammond believes, for example, that future systems may be able to generate more electrical power than today’s traditional systems while costing less to produce. The group is also seeking to show that other key elements of the fuel cell can be made the same way as the membranes.
Still, she’s optimistic commercialization of the system isn’t far off. “I think we’ll have something ready in three to five years,” notes Hammond.