New fuel-cell materials could pave the way for practical hydrogen-powered cars

Hydrogen fuel cells promise clean cars that emit only water. Several major car manufacturers have recently announced their investments to increase the availability of fuelilng stations, while others are currently rolling out new models and prototypes. However, challenges remain, including the chemistry to produce and use hydrogen and oxygen gas efficiently.

In the July 15 edition of ACS Central Science, two research teams report advances on chemical reactions essential to fuel cell technology in separate papers.

Hydrogen (H2) fuel cells combine H2 and oxygen (O2) gases to produce energy. For that to happen, several related chemical reactions are needed, two of which require catalysts.

The first step is to produce the two gases separately. The most common way to do that is to break down, or ''split,'' water with an electric current in a process called electrolysis. Next, the fuel cell must promote the oxidation of H2. That requires reduction of O2, which yields water.

The catalysts currently available for these reactions, though, are either too expensive and demand too much energy for practical use or they produce undesirable side products. So Yi Cui's team at Stanford University, and James Gerken and Shannon Stahl at the University of Wisconsin, Madison independently sought new materials for these reactions.

Cui, an associate professor of materials science and engineering at Stanford and of photon science at the SLAC National Accelerator Laboratory, worked on the first reaction, developing a new cadre of porous materials for water splitting. Cui and his Stanford team used Earth-abundant cobalt-nickel-iron oxides, which are inexpensive and very stable, splitting water continuously for more than 100 hours, significantly better than what researchers have reported for most other non-precious metal materials.

On the side of oxygen reduction, Gerken and Stahl showed how a catalyst system commonly used for aerobic oxidation of organic molecules could be co-opted for electrochemical O2 reduction.

Despite the complementary aims, the two studies diverged in their approaches, with the Stanford team showcasing rugged oxide materials, while the UW Madison researchers exploited the advantages of inexpensive metal-free molecular catalysts. Together these findings offer promising new techniques for moving fuel-cell technology forward.

The authors of both studies acknowledge funding from the U.S. Department of Energy. Yi Cui additionally acknowledges support from the Global Climate and Energy Project at Stanford.