From the Economist this week. This is the second part of the article which has the most relevance to Ballard.
Fuel cells come in several varieties, but the heart of the sort developed by
Ballard is a polymer membrane coated on either side with platinum
electrodes (the platinum also acts as a catalyst). On one side of the
membrane, hydrogen is decomposed into its constituent electrons and
protons. The electrons disappear into the electrode, while the protons pass
through the membrane. On the other side the electrons return via the second
electrode, having passed through the coils of an electric motor that drives the
wheels of the car. Here, they recombine with the protons, and also oxygen
atoms, to make water.
One source of high cost is obvious enough—the platinum. The amount
needed has already been reduced, but it will have to be cut further. A
second is the grooved graphite plates that are used to direct the flow of
hydrogen and oxygen. These are being replaced with cheap carbon
composites. On their own, these and similar economies should bring the cost
of a kilowatt of output down to around $20, if as many as 250,000 engines
a year were produced. But a fuel-cell engine is more than a stack of cells. If
it is ultimately fuelled by methanol, it needs a chemical reactor, known as a
reformer, to release the hydrogen. It also needs an efficient—but
cheap—electric motor.
Reformers are bulky and expensive. Efforts to shrink them have run into problems, according to Firoz Rasul, Ballard's boss. The main one is that smaller reformers produce too much carbon monoxide. Besides diminishing the fuel cell's green credentials, this “poisons” the platinum and stops it doing its job. So far, nobody has come up with an answer to this difficulty that does not involve shifting to another, presumably more expensive, source of hydrogen.
As for the motor, the main problems are that its magnets are made of
molybdenum and titanium—both pricey—and that it needs a complex array
of special switches called thyristors to control it. So yet another result that
the organisers hope will come out of the road trials is some way of
simplifying this electronic control system.
As the test cars paraded outside Sacramento's capitol building, their
designers were no doubt keeping their fingers crossed that these difficulties
will go away. But at least the photo-opportunity was alluring: it was a
beautiful, smogless day. Some time, if their dreams work out, all Californian
days, even in Los Angeles, may be like that. |
