Hydrogen tries again

Has the lightest and most abundant stuff in the universe found a new role in energy?

HAVING soared on the promise of carbon-free motoring, the idea of the “hydrogen economy” crashed and burned when it collided with reality. Hundreds of experimental hydrogen-powered cars—once hailed as the best solution for reducing America’s dependence on foreign oil for over half its consumption—are now gathering dust in manufacturers’ parking lots.

Hydrogen’s main attraction is that when it is “burned” in a fuel-cell or an internal-combustion engine, the only emissions are heat and a wisp of water vapour. Using hydrogen as a fuel—actually, it is more accurate to refer to it as an energy carrier, since producing hydrogen requires energy from another source—therefore has the potential to reduce emissions of greenhouse gases and other pollutants. As America has abundant supplies of coal and natural gas from which hydrogen can be made, what’s not to like about it?

Several things. First, making fuel-cells compact and cheap enough to drive an electric vehicle is far from easy. Over the past 20 years, Honda—arguably the furthest down the road—has been through at least three iterations of its fuel-cell design, and is still one or possibly two generations away from having something practical to offer the motoring public. By comparison, getting a conventional internal-combustion engine to burn hydrogen instead of petrol is relatively easy. Even so, such efforts have also come to naught.

From the beginning, the cloud hanging over the whole hydrogen enterprise has not been the power source as such, but the intractable difficulty of distributing and storing the stuff. It is not hard to see why. Hydrogen atoms are the smallest and lightest in the universe. The next heaviest element in the periodic table, the inert gas helium, is used for detecting cracks in pressure vessels and the like. Even though helium atoms are four times chunkier than hydrogen atoms, they are still small enough to find all the weak spots as they worm their way through the crystalline structure of solid steel several centimetres thick. If hydrogen were used as a crack detector (it is not because of the fire hazard), it would escape four times faster.

Devising a fuel tank to constrain hydrogen has always been a challenge. To have a useful range of 480km (300 miles) or so, an electric car using a fuel cell instead of a battery pack would require around 9kg (20 pounds) of hydrogen. Storing hydrogen as a gas or liquid in a vessel containing “reversible” crystalline metal hydrides is one way to carry it around. Another is to use high-tech pressure vessels made of carbon-fibre. Some researchers are working on sponges made of carbon nanotubes that soak up hydrogen. Whichever technology is chosen, a vessel for storing hydrogen on-board a car costs hundreds of times more than a conventional petrol tank.

Meanwhile, transporting hydrogen from its production facility has presented other difficulties. Natural-gas pipelines cannot be used because hydrogen makes the steel tubing brittle and attacks the welds. Special production processes are needed to make pipes for carrying hydrogen. For that reason, few exist. The alternative is to liquefy the hydrogen at great expense and transport it in road tankers refrigerated with liquid nitrogen. Either way, the hydrogen fuel finishes up costing way too much. And all this assumes that hydrogen can be made cheaply and without producing large amounts of carbon emissions. So far, it can’t.

Such annoying realities have an annoying way of making themselves felt. When they finally did, General Motors ditched its fleet of 100 Chevrolet Equinox fuel-cell cars after a two-year trial. Likewise, BMW withdrew its own test fleet of 100 cars with internal-combustion engines modified to run on hydrogen. The final blow was last year’s announcement by Steven Chu, America’s Noble physics laureate turned energy secretary, that he was cancelling funding for research into hydrogen-powered vehicles generally. Ever since, carmakers have been placing their low-emission bets more on plug-in hybrids, clean diesels or pure electric vehicles.

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