Researchers have developed a new system for storing hydrogen that could pave the way for greener cars.

Hydrogen is thought to be an ideal fuel because it produces only water as a combustion byproduct, but it hasn't been practical for use in automobiles because of the lack of a safe, efficient storage system.

One method that has been tried involves infusing a metal lattice structure with hydrogen cells. When an electric current is applied to the hydrogen-rich metal tank, it releases hydrogen cells. But in order to put the hydrogen in the metal and hold it there requires temperatures in the tank to be above 300 C.

Hydrogen can also be stored as a liquid to increase its density and allow for an efficient amount to be stored in a tank, but only at liquid nitrogen (-198 C) temperatures.

Researchers at the University of Bath in Britain said they have discovered an organic-metal compound that allows hydrogen to be stored at room temperature and released at the flick of a switch, solving the problem of how to keep hydrogen fuel safely aboard a vehicle.

"The problem of how to store hydrogen has been a major bottleneck in the development of the hydrogen power technology," Dr. Andrew Weller of the university's department of chemistry said in a statement.

Weight a major problem

One of the only issues for the material is weight. The U.S. Department of Energy says hydrogen gas should comprise six per cent of the weight of a hydrogen fuel tank in order to give hydrogen-powered cars the same kind of mileage per tank of fuel as petrol-based systems.

The problem is hydrogen's lack of density: it takes up roughly four times as much space as gasoline, meaning it needs larger fuel tanks.

The density of the new organic-metal compound adds to the problem, since it uses rhodium, a metal similar to platinum.

It makes a proposed storage tank using the material too heavy for the fuel inside. At present it has a fuel to weight ratio of 0.1 per cent, too low to hold enough fuel to be practical.

But Weller said that if used in combination with a metal lattice system, the material could provide a car at rest a kickstart until the temperature reaches 300 C.

"It could certainly fill the time lag between a driver putting their foot on the accelerator and a metal hydride fuel tank getting up to temperature," Weller said.

"We are really very excited about the potential this technology offers."

The researchers hope to have a working prototype ready within three years.