Ammonia pellets deliver hydrogen to cars of tomorrow

Ammonia pellets deliver hydrogen to cars of tomorrow

While hydrogen may eventually be the fuel of choice for the automobile of tomorrow, there are still questions about techniques for safely storing and dispensing the fuel. Scientists at the Pacific Northwest National Laboratory (Richland, WA) are closer to answering those questions with a novel storage technology using small (240-mg) pellets of solid ammonia borane (AB) to hold relatively large quantities of hydrogen (0.5 l) in a very small volume.

“With this new understanding and our improved methods in working with ammonia borane we’re making positive strides in developing a viable storage medium to provide reliable, environmentally friendly hydrogen power generation for future transportation needs,” said Dave Heldebrant, a PNNL scientist.

The laboratory is part of the DoE’s Chemical Hydrogen Storage Center of Excellence. Each milliliter of AB weighs about 0.25 g and can hold up to 1.8 l of hydrogen. Researchers expect that an ammonia-borane-based fuel system will occupy less space and be lighter in weight than systems using pressurized hydrogen gas, thus enabling fuel cell vehicles to have room, range, and performance comparable to today’s automobiles.

Currently, PNNL scientists are learning to manipulate the release of hydrogen from AB at predictable rates. By varying temperature and manipulating AB feed rates to a reactor, researchers envision controlling the production of hydrogen and thus fuel-cell power, much like a gas pedal regulates fuel to a car’s combustion engine.

“Once hydrogen from the storage material is depleted, the AB pellets must be safely and efficiently regenerated by way of chemical processing,” said Don Camaioni, a PNNL scientist. “This refueling method requires chemically digesting or breaking down the solid spent fuel into chemicals that can be recycled back to AB with hydrogen.”

Ralph Raiola