Bath researchers gas up green cars

Researchers at Bath University have developed a new hydrogen storage technique they think could pave the way for greener cars.

Hydrogen-powered cars have long been touted as the ultimate in environmentalist transport because they produce no pollutants - only water vapour. But how to safely store the hydrogen fuel has been something of a problem.

One proposed solution - locking the gas away in a metal lattice - works wonderfully, but only at very high temperatures. An alternative - using a metal organic framework - is only feasible at liquid nitrogen (-198°C) temperatures.

The new technology allows hydrogen to be stored at room temperature and released at the flick of a switch. This solves the problem of how to store hydrogen fuel safely on board a hydrogen-powered vehicle, the researchers say.

The team was investigating the effect of hydrogen on metals when they discovered an organo-metal compound that would absorb hydrogen at room temperature and release it upon application of a small electric current.

This kind of take up and release at the atomic scale makes the material an ideal candidate for solving the hydrogen storage problem, the team explained.

The storage to weight ratio of the Rhodium storage technique is too low to use for an entire tank and still meet US department of energy efficiency requirements*. However, the researchers propose the technology as a short term fuel storage that would power the car until the engine reached the 300°C needed for the metal hydride lattice to kick in.

"Hydrogen has a low density and it only condenses into liquid form at -252°C so it is difficult to use conventional storage systems such as high-pressure gas containers which would need steel walls at least three inches thick, making them too heavy and too large for cars," notes Dr Andrew Weller from the Department of Chemistry at the University of Bath.

"Our new material works at room temperature and at atmospheric pressure at the flick of a switch. Because it is made from a heavy metal (Rhodium), its weight to fuel ratio is low, 0.1 per cent, but 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."

The team hopes to have a working prototype built in the next two to three years.

The research has been published in the journal Angewandte Chemie in August 2006, and reviewed by Nature in September 2006. ®

*Six per cent of the weight of hydrogen storage systems must be hydrogen, so that hydrogen-powered cars have the same kind of mileage per tank as petrol-based systems.