One problem that has been plaguing the development of hydrogen-fueled vehicles is that hydrogen gas needs to be stored and transported in expensive pressurized tanks. Liquid energy carriers such as hydrogen dissolved in a salt solution are viewed as possible alternatives, but they’re also fraught with problems including the accumulation of byproducts. The simplest hydrogen carrier is water. But splitting hydrogen from oxygen requires, besides catalysts, a lot of energy.
But now a research group called Team FAST, comprising students at the Technical University Eindhoven (TUE), in the Netherlands, thinks it has the hydrogen storage problem licked. To supply the one-meter-long scale model fuel cell vehicle they’ve developed with as much hydrogen as it needs, they’ve turned to formic acid (HCOOH). The liquid compound that can be created by joining carbon dioxide molecules with hydrogen with the help of catalysts and stored under atmospheric pressure. What’s more, catalysts can do the job of splitting formic acid into hydrogen and CO2—without an external energy source.
Though this idea is not new, the efficiency of catalysts had been too low to deliver a stream of hydrogen sufficient to run fuel cells that could power a car. That is, until research completed last year by Georgy Filonenko, a recently-departed graduate student there, led to the discovery of a catalyst that is 10 times as efficient.
"The catalyst is a ruthenium complex which dissolves in the formic acid, and it is so active that you need only, what I call 'homeopathic' quantities, to dissociate the formic acid,” says Emiel Hensen, a chemist who supervised Filonenko's PhD research. Besides being required in small quantities, the ruthenium complex is, unlike other catalysts, not fouled by air or water, facilitating its use in a automotive applications, says Hensen.
To test out the advance, the FAST team set out, a year and a half ago, to build a working an one-meter scale model of a hydrogen car. It contains an off-the-shelf fuel cell and a catalytic reactor the size of a coffee mug, explains Pieter Ottink, who is the spokesperson for the team. Having shown off this proof-of-concept version, they say the next step is to power a full-scale model, hopefully by the end of this year. The team also reports that they have struck a deal with a company that will supply them with a hydrogen bus.
“We are not yet sure about how we will design the big system; scaling up a chemical reaction like this is dependent on a lot of variables,” says Ottink. However, they plan to proceed carefully. “It does not seem to be efficient to make one big reactor, so we will [likely equip the bus with] multiple small ones,” he says. But who knows? “This technology is in a very early stage," Ottink adds.
A fortuitous coincidence will certainly make things easier, however. “The catalytic reaction is efficient at around 80 degrees C, so you should warm it up. We have the advantage that the fuel cell also produces heat, and this heat can be used to warm up the reactor,” says Ottink.
Unfortunately, the CO2 liberated during the catalytic reaction is released into the air. But if the formic acid can be produced in a sustainable way—by, say, drawing CO2 from the flues of fossil-fueled power plants—the process would be carbon neutral.