More news from:  Science  |  Environment  |  Health
How and Why

Hydrogen-powered car still seems improbable

Hydrogen-powered cars may be able to claim zero emissions, but powering up their fuel cells can be environmentally expensive.
Hydrogen-powered cars may be able to claim zero emissions, but powering up their fuel cells can be environmentally expensive. (Alamy)

Network News

X Profile
View More Activity
By Curt Suplee
Tuesday, November 17, 2009

Just in time for Thanksgiving, a familiar techno-turkey is back on the national policy table: the hydrogen-powered car. The Obama administration had flatlined funding for President George W. Bush's pet initiative, briefly but heavily touted a few years back as the driving force toward a future "hydrogen economy" in which gas would displace gasoline.

Two wars and a financial sinkhole later, most Americans had managed to forget the whole thing. But then last month the Senate improbably restored $187 million for H-car research programs to an appropriations bill.

Okay, that's barely enough to cover one year's bonuses on the lower floors at AIG. But why is it there at all? The answer lies in the persistent, hypnotic allure of hydrogen eco-mythology, with its promise of breaking our addiction to fossil fuels and foreign oil while banishing greenhouse pollution from our skies -- a vision most pointedly embodied in the hydrogen car. Or, more accurately, the notion of the hydrogen car.

The prototypical H-car is powered by electrical current from a fuel cell, a device that combines hydrogen and oxygen to produce electricity. The principle involved is a schoolroom classic: If you stick two electrodes into a beaker of water, the electrical energy breaks H2O apart into its ingredients, H and O, in a process called electrolysis. A fuel cell does the same thing in reverse, putting separate H's and O's back together into water molecules and thereby producing electrical energy, which can be used to run a motor.

It is this reaction that allows H-car proponents to state (in a mantra repeated so often that is accepted as gizmo gospel by many intelligent adults) that a fuel-cell vehicle's "only emission is water vapor." That is true, but only in a trivial and thoroughly misleading sense.

To understand why, you need to recall two fundamental facts. The first is that, unlike oxygen, hydrogen doesn't grow on trees. Although it's the most common element in the cosmos, it isn't found in a pure state on our planet. There are no subterranean "hydrogen pockets" equivalent to coal beds or natural gas deposits. Hydrogen has to be extracted from compounds into which it is firmly bound and which it really doesn't want to leave.

The standard method, which is used in 95 percent of all U.S. hydrogen production today, is to strip it out of natural gas, a procedure that generates copious emissions of carbon monoxide and carbon dioxide, though probably not as much as burning the gas outright. This method, of course, consumes fossil fuel -- the very scenario that the hydrogen car was intended to avoid in the first place.

Alternatively, you can get hydrogen from coal or alcohol (with emissions ditto), or you can coax it out of other chemical reactions, or you can breed bacteria to exhale it. And, of course, you can get it out of water by electrolysis.

Each method has an energy cost, which brings us to the second fundamental fact: The energy we consume usually has changed forms repeatedly by the time we get it. Turn on a toaster and you're using electrical energy to create heat energy. But the electrical energy originally came from chemical energy in coal, which was converted to thermal energy, which was converted to mechanical energy that ran a generator to produce electrical energy.

Such ingenious chains of conversion make modern civilization possible and have enabled the United States to lead the free world in production of wall-mounted singing rubber fish. But nature extracts a substantial tariff on each transaction; that is, some energy is always lost. No conversion can be 100 percent efficient, and many are far, far less.

A conventional automobile engine is able to convert into useful work maybe 25 percent of the chemical energy in gasoline. The energy in the light from an incandescent bulb represents about 2 percent of the chemical energy in the coal that was burned to make the electricity that powers the bulb.

The latest hydrogen fuel cells are about 50 to 70 percent efficient, so they might start to look pretty good, even if they're ferociously expensive and require scarce platinum as a catalyst.

But why would you want to store energy in the form of hydrogen and then use that hydrogen to produce electricity for a motor, when electrical energy is already waiting to be sucked out of sockets all over America and stored in auto batteries -- all without a middleman?

Moreover, even if pollution-free hydrogen were available -- produced, say, by electrolysis using zero-emissions energy from wind turbines -- you'd still need a way to move enormous amounts of it around the country the way gasoline is delivered now. That raises a whole new set of problems. Hydrogen has relatively low energy content per unit volume, about one-third that of natural gas or gasoline. So it would have to be tightly compressed, probably to thousands of pounds per square inch, all without leaks of the highly flammable stuff that could turn the corner "gas" station or family sedan into a mini-Hindenburg.

None of that is impossible. It's just stupendously difficult and probably pointless. That's why, for the foreseeable future, the hydrogen car will remain a tailpipe dream.


© 2009 The Washington Post Company

Network News

X My Profile
View More Activity