Hydrogen is one of the cleanest-burning fuels known, but storing and transporting it can be a problem as anyone who's seen footage of the Hindenburg disaster knows. But researchers at Germany's University of Rostock say they've come up with a solution that could make hydrogen fuel safe and practical, by storing it as liquid methanol.
Not that this hasn't been proposed before. It's easy enough to make methanol from hydrogen; all you need is some carbon and a little oxygen, and any of a number of chemical processes will get you there. The trick, however, is getting the hydrogen back out again when you want to burn it.
Hydrogen fuel cells are twice as efficient as fuel cells that burn methanol, but extracting hydrogen from methanol has meant heating the methanol to 200° C at high pressure which is hardly practical, given that the goal is to burn hydrogen as fuel, not to burn fuel to extract the hydrogen.
But Matthias Beller and his team at the University of Rostock say they've figured out a way to get hydrogen out of methanol at much lower temperatures, and at ambient pressure.
The key to Beller's research, which was published in the journal Nature on Wednesday, is a new kind of soluble catalyst based on the rare metal ruthenium. By adding this material to his chemical process, Beller says he was able to extract hydrogen from uncompressed methanol at temperatures between 65° and 90° C.
That's still hot water at 65° C is scalding but according to Edman Tsang of the University of Oxford, such temperatures are within the range of the waste heat produced by an operating fuel cell.
That means some of that waste heat could potentially be harnessed to power the reaction that releases more hydrogen from the methanol, making Beller's method more energy-efficient than other recently proposed methods, such as extracting the hydrogen using nano-materials.
Just how efficient it is, though, is hard to say. "It is difficult to estimate how much energy will be saved," Beller says.
And there are still problems with Beller's method, not least of which will be obtaining the ruthenium needed for the catalyst. So far, Beller has only been able to keep the catalyst stable for three weeks, which means it could need to be renewed often. And yet ruthenium is extremely rare, with current global reserves estimated at around 5,000 tonnes. By comparison, more than 2,000 tonnes of gold are mined each year.
Worse still, Beller's reaction produces a lot of carbon dioxide that infamous bugbear of climate scientists an unfortunate side effect that could sully hydrogen's reputation as a clean fuel, unless the CO2 could somehow be prevented from escaping into the atmosphere.
But such concerns are still a long way off for Beller, whose current problem is scaling his reaction to a level where it could be commercially viable. A hydrogen-powered car engine would burn about 24 liters of the gas per second. So far, the rate at which Beller has been able to extract hydrogen from methanol can be measured in just milliliters per minute. ®