Scientists are making significant headway in finding alternatives to power automobiles without polluting the atmosphere.

Great hopes have been vested in hydrogen fuel cells since their use in spacecraft in the 1960s. They are now being used for stationary power generation and material handling equipment, and the prospect of a commercially viable system for powering automobiles has moved a significant step closer, thanks to advances in applied research and development at the U.S. Department of Energy’s (DOE) National Laboratories. Novel fuel-cell technologies, including advanced catalysts and membrane electrode assemblies (MEAs) have been developed over the past few years, offering a major option for a clean alternative to gasoline engines. Next-generation catalysts are yielding improved activity and durability, making fuel cells suitable for a mass market.

According to senior researchers, the new catalysts give high performance with a big enough reduction in cost per kilowatt to make fuel cells potentially competitive with conventional technologies used in automobiles. The biggest cost item is the catalyst, reflecting the high price of platinum, so far found to be the most suitable material.

Three National Laboratories—Los Alamos National Laboratory (LANL) in Los Alamos, New Mexico; Lawrence Berkeley National Laboratory (Berkeley Lab) in Berkeley, California; and Brookhaven National Laboratory (Brookhaven), in Upton, New York—have been pioneers in the advancing the state of the art of fuel-cell catalysts and moving the technology toward the mass consumer market. Most recently, Brookhaven has pioneered a method using much smaller quantities of platinum with improved results. This involves working with nanoparticles of a support material and coating them with a skin-like layer of platinum. Compared with current-generation fuel cells using pure platinum, this approach reduces platinum content by 90 percent.

This advancement would not be possible without prior work carried out at Berkeley Lab and LANL. Berkeley Lab prepared catalysts with platinum on the surface of platinum alloys and discovered that catalysts with this structure perform better than conventional platinum catalyst particles, due to the effects of layering and alloying.

LANL researchers incorporated an ionomer into the electrode, increasing proton conductivity, and pioneered an approach to catalyst deposition on thin-film electrodes. These improvements mean that less platinum (by more than a factor of 20) is necessary for the same or better performance, which enables the use of nanoscale particle catalysts. The new catalysts have been incorporated into MEAs and tested with encouraging results at LANL and some private companies.

Catalysts are used in both electrodes of a fuel cell to maximize the electrochemical reactions, in which hydrogen and oxygen combine to produce not just water but also—by making hydrogen’s electrons pass through an external circuit—an electric current. The Brookhaven team first created a catalyst using the new approach for the positive anode terminal, where hydrogen enters the fuel cell. An alloy of platinum and ruthenium, a metal of the same group, had already proved efficient. Under the new approach, an ultrathin platinum monolayer was deposited on ruthenium particles, making almost all the platinum atoms available to react with the hydrogen.

The combination is useful in dealing with one of the factors impairing the performance of fuel cells—the accumulation of tiny traces of carbon monoxide, which are expensive to remove, are poisonous and bond to the platinum, preventing hydrogen oxidation. Ruthenium catalyzes the oxidation of this carbon monoxide into carbon dioxide, which is harmless to the cell.

The team has worked on similar techniques using other core materials and developing more elaborate combinations, with one outer shell on top of another. One of the most promising involves a core of palladium coated with platinum, which is then sprinkled with gold clusters. Gold has been shown to be effective in making the catalyst at the negative cathode more resistant to corrosion, keeping the platinum intact. The tendency of platinum to lose its activity and affect fuel-cell performance in stop-and-go driving conditions has been one of the big obstacles to a satisfactory automobile system. Another promising combination is an alloy of platinum with nickel and copper. Under certain operating conditions, this alloy performs three times better than standard catalysts.

The DOE Hydrogen Program’s goal, to overcome obstacles to taking hydrogen fuel-cell vehicles from the laboratory to the showroom, now appears to be within reach. In 2004, the program began implementing a $1.2 billion Hydrogen Fuel Initiative, with the goal of reducing both petroleum dependence and greenhouse gas emissions. The principal emphasis has been on personal transportation, the sector with the greatest potential on both counts. U.S. transportation is responsible for about one third of carbon dioxide emissions and two thirds of petroleum use, and light-duty vehicles account for most of that.

Priority has been given to fuel cells using polymer electrolyte membranes. These solid electrolytes can operate at reasonably low temperatures, avoiding long startup times, and provide the power density needed for automobiles. Other uses include forklifts and back-up power for telecommunications.

But the search for a low-platinum, high-performance catalyst has been a long one. “It’s not something that happens overnight,” said JoAnn Milliken, manager of the Hydrogen Program. To be sure, similar cost and reliability hurdles exist for the competing option of rechargeable batteries.

Fuel cell costs have already come down from $275 per kilowatt in 2002 to around $75 per kilowatt, with a 2015 target of $30 per kilowatt, which would be competitive with conventional gasoline engines. System durability has reached almost 2,000 hours, on the way to a target life of 5,000 hours, equivalent to 150,000 miles. Higher durability has already been demonstrated in single laboratory cells.

If technical targets are reached by 2015, it is expected to be another five years before affordable hydrogen cars enter the market, although automobile manufacturers say they can introduce the cars sooner—if, that is, hydrogen is available for fueling. “I think it’s the logistics of providing the fuel— building the infrastructure—that will determine whether hydrogen fuel cells will make it.” Milliken said. But scientists are confident that fuel-cell technology will pass the test.