Benziger and Woo '06 design more efficient hydrogen cells

A new type of hydrogen fuel cell promising 100 percent efficiency has emerged from the senior thesis research of Claire Woo '06 and her adviser, chemical engineering professor Jay Benziger.

To operate efficiently, current fuel cells need complex systems to control humidity and recover and recycle fuel. They are, at most, 40 percent fuel-efficient.

Benziger and Woo — who is now a graduate student at the University of California at Berkeley — simplified the old system, eliminating an additional humidifying system that had preceded the reaction chamber. Additionally, they removed recovery and recycling systems.

With gasoline-powered engines, "you burn as much oil as you want [in order] to control how fast your car goes," Woo explained. But, she noted, the same need-based efficiency had yet to be achieved in a fuel cell.

Her new fuel cell uses gravity to drain excess water out of the reaction chamber. The water is then caught in water reservoirs. When there is an excess of gas, the cell pushes the water into the drainage system. When gas flow drops, the reduction in pressure in the chamber draws the water back into the chamber.

Benziger said the idea for the fuel cell first came about in 2005, when students built a model cell for an experimental system. During that time, he recalled, an exchange student from Australia suggested that the model might eliminate the need for a humidification system in real fuel cell designs. For her senior thesis, Woo decided to try to make that suggestion a reality.

Benziger said that of all the senior theses on fuel cells he has seen in the past six years, Woo's was one of two that stood out. Both theses also won senior thesis awards from the chemical engineering department.

In the beginning, Woo said, she had modest hopes for her thesis. "It was surprising, but it succeeded," she said. The success of her model — more than the scientific journal articles written about it and the award from her department — "was the more rewarding part, the more scientifically exciting part of the project," she said.

Though the idea of a hydrogen-powered car has received a lot of hype in past years, Benziger said he does not believe that this is a realistic application of the fuel cell. Battery-powered vehicles "are much more efficient and practical in the long term than a hydrogen-powered car," he said.

"Probably the best applications right now are in backup power systems," Benziger added. "They use them, say, for emergency generators in places like hospitals and things. In California, they use a lot of fuel cells for backup power for servers."

The fuel cell could also be used in tandem with wind and solar power — intermittent sources of energy that require an auxiliary system to provide energy when the wind is still or the sun is not shining.

"You can electrolyze water with some of the electricity generated by wind or power, store the hydrogen, and then later, or in peak demand, you can convert that hydrogen back into electricity," Benziger explained. "It becomes a way to have portable storage for energy more efficiently than batteries."