Hydrogen car gets gas

While hydrogen has been touted as the fuel of the future for vehicles, safe and efficient on-board storage of the gas remains a major hurdle in developing practical vehicles. Now, researchers at the University of Bath, U.K., have developed a rhodium phosphene-based material that absorbs hydrogen and releases it nearly instantaneously at room temperature and atmospheric pressure when a slight voltage is applied.

While the compound isn’t suitable for storing all the hydrogen needed, it can play an important role in making vehicles viable, says Andrew Weller of the school’s department of chemistry, by handling demand when quick bursts of the gas are needed. “Hydrogen storage capacity isn’t the issue, but rapid release at room temperature is,” he stresses.

“The U.S. Department of Energy has said that it wants 6% of the weight of hydrogen storage systems to be hydrogen to give new hydrogen-powered cars the same kind of mileage per tank of fuel as gasoline-based systems,” Weller notes. “While metal hydrides and metal-organic-framework materials can achieve this kind of ratio, they only work at extremes of temperature that are difficult to engineer into an ordinary vehicle,” he adds. Although the new material’s fuel-to-weight ratio isn’t high enough to handle all hydrogen storage, the compound could fill the time lag between a driver stepping on the accelerator and a metal-hydride fuel tank getting up to temperature, Weller believes. Ultimately, such a compound might handle 10% to 15% of the necessary hydrogen storage, he hopes.

Each molecule of the compound absorbs two molecules of hydrogen and strongly retains the hydrogen, even under vacuum, but releases the gas in 170 ms. at room temperature and atmospheric pressure when 1V. is applied, he explains. Because it is made from a heavy metal, the new material’s weight-to-fuel ratio is low, 0.1%, but Weller foresees getting up to 1½% to 2% total weight of stored hydrogen by developing similar compounds based on lighter metals.

A hydrogen storage tank could be created by depositing the material onto sheets that could be stacked together and encased. The first prototype, expected to be completed within a year, will be rhodium phosphene-based. The second prototype, likely in two to three years, should use a lighter and cheaper metal, Weller notes.

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