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Membrane Magic

One way to extend the range of the electric car is to carry fuel and generate electricity onboard. This is the approach used by hybrid gasoline-electric cars such as the Toyota Prius, which hit U.S. showrooms this summer. The Prius employs a small, efficient combustion engine, plus a pile of batteries that supplement the engine during acceleration and absorb power from the wheels during braking. The problem with this solution is that it is inherently complicated and costly, since it combines electric and mechanical drive technologies. Robert Winters, a power technologies analyst with Bear Stearns in New York, says that the Prius is “heavily subsidized,” and wonders whether hybrids will ever be affordable. “You’ve got a redundant engine system in there. How are you going to overcome that?”

Enter the fuel cell. Unlike batteries, which store a charge, fuel cells generate electricity on the fly. Carry enough fuel, and the fuel cell will take your electric vehicle wherever you want to go. Winters says fuel cells are rapidly becoming a commodity, and vehicles carrying them could easily account for “several percent” of the 60 million or so cars that will be produced worldwide by 2010.

Though fuel cells come in half a dozen varieties, utilizing different fuels and materials, one version has emerged as the clear favorite for automotive use: the proton exchange membrane (PEM) fuel cell. A PEM cell is solid and compact and operates at a relatively cool 80 C. The heart of the PEM cell is a rubbery plastic membrane coated with a platinum catalyst. The catalyst splits hydrogen gas into protons and electrons; only the protons can pass through the membrane. The electrons travel around the membrane, generating the treasured electric current, before recombining with the protons and oxygen on the other side of the membrane to generate water. Stacking a series of these membrane-catalyst assemblies, or “cells,” multiplies the voltage.

PEM stacks lit the Gemini spacecraft that circled Earth in the 1960s, but generated a trickle of electricity too weak and expensive for commercial applications-let alone automobile engines. Then, in the late 1980s, researchers at Los Alamos National Laboratory made major advances in catalysts, reducing by 90 percent the amount of platinum required. Ballard multiplied the stack’s power density-the power returned per unit of precious vehicle space it occupies-by learning how to keep the membranes happy (wet but not soaked) and by perfecting the plumbing that moves hydrogen, oxygen and water through the stacks. Ballard, based in Burnaby, B.C., has close to 400 patents issued or pending to protect its lead in PEM technology.

Two years ago Ballard exceeded the minimum power density for automobiles-1,000 watts per liter-with its Mark 700 stack, two of which propel Commander II. Ballard’s Mark 900 stacks, released early this year, put out as much as 1,350 watts per liter. “That’s a power density that is practical for today’s vehicles,” says Paul Lancaster, Ballard vice president for finance. In other words, a car packing such a stack should accelerate the family road machine, luggage included, with the same gusto as an internal combustion engine.

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