The Economist

April 5, 2000

How green is your hydrogen?

FUEL cells, which generate electricity by reacting
hydrogen and oxygen together, and thus yield water as
their exhaust, may sound like the answer to
environmentalists’ prayers. Most big car makers
certainly hope they are. They are spending huge sums of
money on what may turn out to be the 21st century’s
replacement for the internal-combustion engine. But just
how clean a fuel cell really is depends on the answer to
a dirty little question: where, exactly, did the hydrogen
that powers it come from?

That a fuel-cell-powered vehicle does not muck up its
immediate environment is unquestioned—and it is a
good thing in its own right. But the naive might assume
that the lack of carbon in its fuel means that a fuel cell
cannot contribute any carbon dioxide to the
atmosphere, and thus will not have any effect on global
warming. That is frequently wrong.

In an environmentally ideal world, the most elegant
option would be to produce hydrogen directly by the
electrolysis of water, using electricity generated from
renewable energy. However, this is unlikely to be
economic in the immediate future, except in a few
countries, such as Iceland, that have abundant
hydroelectric or geothermal power.

The alternative is to get the hydrogen by stripping it from
hydrocarbon molecules of the sort found in fossil fuels.
Current prototypes do this on board a vehicle in an
apparatus called a reformer. But the chemical processes
used in reformers release the surplus carbon as carbon
dioxide.

That may, for the moment, be inevitable. But a report
just issued by the Pembina Institute, a Canadian
research group, suggests that the hydrocarbon fuels
most likely to make it to market are also the ones that
do the least to cut greenhouse-gas emissions. The report
tries to calculate the “well to wheel” release of
greenhouse gases (mostly carbon dioxide) for a variety
of fuels—in other words, the amount of greenhouse gas
released as a result of the extraction, refining and
transport of the fuel, and its use to power a car for
1,000km. The smallest improvements over current
technology came from so-called “clean” petrol (ie, with
all nasties such as sulphur removed) and methanol, fuels
favoured by the car and oil companies. The best result
was obtained with natural gas.

That is not surprising. Natural gas is mostly methane,
which has four hydrogen atoms for every carbon
atom—the maximum that is physically possible for a
hydrocarbon. And yet what is worrying is that the big
firms are largely ignoring natural gas as a source of
hydrogen.

It is also curious. One of the things that car companies
fret about is how fuel will be delivered in a fuel-cell
world. Hydrogen and methanol, at least, would require
a whole new infrastructure. But natural gas would not. It
is already widely on sale, although not at the petrol
stations so dear to oil firms.

Gas is also easy and efficient to reform into hydrogen.
That is not true for methanol. And it is cheap. According
to Richard Stobart of Arthur D. Little, a consultancy
that has investigated the matter, the running costs to a
driver of a fuel-cell car that gets its hydrogen from
natural gas would be comparable to those of one that
used clean petrol.

The only serious objection to natural gas is that, even
when compressed or liquefied, it takes up a lot of
space. In the short run, that might restrict natural-gas
use to vehicles such as lorries and buses, where space is
at less of a premium (and which already run on a
different fuel from most cars). In the longer run,
however, it should be a soluble problem.

One promising idea is to extract the hydrogen from
natural gas in large reformers located at filling stations,
and then store it on board vehicles in solids known as
metal hydrides. The latest versions of these, such as one
recently unveiled by a Detroit-based firm called Energy
Conversion Devices, soak up hydrogen so well that a
tank of hydride can deliver as much energy as a
same-sized tank of petrol. This technology might be
ready for market within a couple of years. Or perhaps a
few show-off greens will resort to an expedient that was
seen in wartime Britain—huge gas bags on top of their
vehicles. That way they will be able to proclaim their
saintliness in a form that all can see.