Fuel-Cell Researchers Look to Carbon

A group of researchers has developed a new method of layering graphite that could be used someday to efficiently and safely store hydrogen in a vehicle.

If their preliminary findings hold up under more experimentation, carbon-based storage may have the most potential, among several technologies now being considered, to make fuel-cell vehicles commercially viable.

Published in the July 26 issue of the Proceedings of the National Academy of Sciences, the study claims that earlier research underestimated the potential capacity of carbon materials to store hydrogen. According to John Tse, one of the authors of the study and a professor of physics at the University of Saskatchewan, graphite nanomaterial can be layered to adsorb hydrogen gas at higher volumes and densities than previously thought possible.

By controlling the spacing of layers of graphitic plates to maximize adsorption, Tse says a graphite storage system could meet the U.S. Department of Energy’s milestones for both weight and volume of a hydrogen storage system. (The study did not consider the DOE’s other two goals: cost and time of refueling.)

“[We think] it is possible store hydrogen at close to the highest theoretical concentration,” Tse says.

The graphitic material is lighter than metal hydrides storage solutions currently being explored, and is relatively cheap to create. Furthermore, it’s chemically inert and environmentally benign. Think of a pencil.

The Bush Administration wants to reduce the use of fossil fuels, by helping the private sector domestically produce hydrogen that could be used in commercial fuel-cell vehicles by 2020. To that end, last year the DOE set increasingly stringent goals for 2005, 2010, and 2015, for the weight, volume, cost, and refueling time of hydrogen storage systems, which it believes should be met for hydrogen-powered vehicles to become commercially viable. (The department employs scientists who evaluate emerging technologies and oversee the progress of federal funding to university and laboratory researchers.)

According to DOE hydrogen program manager Steve Chalk, none of the three methods for absorbing gaseous hydrogen into other materials – carbon, chemical, and metal hydride – has yet achieved all four of the 2005 goals, although individual benchmarks have been met. Creating a viable hydrogen storage platform is “the most critical barrier to the hydrogen economy,” Chalk says.

In addition to DOE-sponsored research at universities and laboratories, a number of companies, including Millennium Cell and Energy Conversion, are developing hydrogen storage systems for fuel-cell vehicles. Although Ford, Honda, and GM are road testing fuel-cell vehicles powered by hydrogen, these cars have limited fuel capacity and do not meet the DOE benchmarks yet.

Earlier this year, the DOE also established three “Centers for Excellence” that provide funding and coordinate research activities for carbon, chemical, and metal hydride hydrogen storage. The department has deemphasized its earlier exploration of liquid or pressurized hydrogen storage because of safety and cost concerns. It will spend $5-6 million annually on each center, according to Chalk.

“It will be very tough for any technology to meet DOE long-term targets from a weight perspective,” says Clemens van Zeyl, president and CEO of Canadian firm Hera Hydrogen Storage Systems.

Hera is developing complex metal hydrides that can absorb and release hydrogen gas. They’re much lighter than hydrides composed of metal alloys such as nickel that were used in earlier research. The company is experimenting with sodium and magnesium-based nanomaterials that are more efficient in bonding hydrogen with metal, says van Zeyl, who hopes to have identified the most appropriate materials by 2007.

Despite the extensive amount of basic research yet to be done, van Zeyl is optimistic that the hydrogen storage challenges will someday be met. “A lot of people are discouraged about hydrogen [as a fuel carrier], but I see a lot of good things happening [in complex metal hydrides],” van Zeyl says.

Dan Benjamin, an analyst at ABI Research, is one of those who is still skeptical. He’s not seen anything in hydrogen storage research indicating that a breakthrough is imminent. He also points out that the DOE goals are very ambitious and “present a considerable challenge” for researchers. However, Benjamin acknowledged some advances in hydrogen storage technology for smaller devices, such as high definition cameras and computers.

According to Chalk, the DOE continually reevaluates its hydrogen program, as more information is garnered about technologies being developed. And, despite the slow progress in hydrogen storage, he remains optimistic that the long-term goals will be achieved, and that fuel-cell vehicles will become a reality.