New anode material bodes well
Pacific Northwest National Laboratory scientist Olga Marina is developing a new generation of non-metallic anodes for solid oxide fuel cells and she is seeing promising results. With support from the U.S. Department of Energy's Office of Fossil Energy, her work is part of a significant international research effort to identify alternatives to nickel in solid oxide fuel cells.
In a fuel cell, the anode facilitates the reaction between hydrogen, carbon monoxide and hydrocarbon fuels with oxygen ions that permeate the electrolyte from the cathode side. An ideal anode should have high electrical conductivity and electrocatalytic activity, and it should be tolerant to intermittent air exposure and sulfur-containing compounds in hydrocarbon fuels such as gasoline, diesel and natural gas.
Traditionally nickel is used in solid oxide fuel cell anodes because it has excellent electrical conductivity and electrocatalytic activity; however, it also has some drawbacks that can lead to deactivation and reduced fuel cell performance. Nickel oxidizes rapidly and may break apart when exposed to air, which can occur during startup and shutdown of the fuel cell system. Nickel also is susceptible to poisoning when exposed to low concentrations of sulfur and promotes a buildup of carbon under certain conditions.
While metal oxides provide better oxidation resistance and sulfur tolerance than metal anodes, these benefits usually come at the expense of significantly lower electrical conductivity and reduced electrochemical activity.
A material that offers a good compromise seems to be the solution and Marina may have found just that. She discovered a new class of materials that provides a good balance among the many anode performance criteria. The composite composed of oxides of strontium titanate and ceria provides excellent oxidation resistance and sulfur tolerance, has electrocatalytic activity comparable to nickel and offers adequate electrical conductivity.
"It's a breakthrough because up until now there has been no good alternative to nickel. This material shows promising performance quite comparable to nickel," Marina said. The metal oxide composite outperforms any other known non-metal fuel cell anode and was announced in July at the European Fuel Cell Forum held in Lucerne, Switzerland. A patent is pending on this invention.