JOHN M. VOHS

Department of Chemical and Biomolecular Engineering

University of Pennsylvania

Philadelphia, Pennsylvania

A fuel cell is a device that converts energy stored in chemical bonds in a fuel directly into electricity with high efficiency (Carette et al., 2000; Minh 1993). Unlike conventional methods of producing electricity, such as steam turbines, the efficiency of a fuel cell is not limited by the Carnot cycle; therefore, fuel cells can have energy-conversion efficiencies of 60 to 80 percent. This makes fuel cells environmentally friendly energy-conversion devices, and they have been proposed for use in applications ranging from large-scale power production to transportation to battery replacement.

Fuel cells were invented more than 150 years ago, but their commercialization has been very slow. To date, they have been used primarily in space vehicles, but these systems are quite costly and not suitable for commercial applications. In the last decade, however, there has been a dramatic increase in research, and it is now clear that fuel cells will enter the commercial marketplace in the not too distant future. Currently, most attention is focused on two types of fuel cells, polymer-electrolyte membrane (PEM) fuel cells and solid-oxide electrolyte fuel cells (SOFCs) (Carrette et al., 2000; Minh 1993). PEM systems use a proton-conducting polymer as the electrolyte and operate at low temperatures; SOFCs use an oxygen ion-conducting ceramic membrane as the electrolyte and operate at temperatures of 700 to 1,000°C.

In a PEM system, the charged species transported through the electrolyte are protons (H⁺); thus, H₂ must be used as the fuel. This requirement presents many challenges for developers of PEM systems because hydrogen is difficult to store and costly to produce. The only viable source of hydrogen today is from the reforming of hydrocarbons (Ogden 2002). PEM systems also require high-puri-

Front Matter (R1-R10)

Chemical and Molecular Engineering in the 21st Century (1-28)

Technology for Human Beings (29-52)

The Future of Nuclear Energy (53-90)

Engineering Challenges for Quantum Information Technology (91-108)

Dinner Speech (109-118)

Appendix: Contributors (119-126)

Appendix: Program (127-130)

Appendix: Participants (131-140)