MATERIALS SCIENCE AND ENGINEERING

MATERIALS FOR SOLID-OXIDE FUEL CELLS

Fuel cells directly convert chemical energy of fuels (e.g. hydrogen or methanol) into electric energy. Several approaches to technical realization of presently under development. One particularly promising concept for stationary fuel cells are solid-oxide fuel cells (SOFCs). SOFCs operate at high temperature (500 to 1000 °C). This enables them to achieve a particularly high conversion efficiency and a low emission rate.

While the attributes of SOFCs are strong, there are several significant materials selection and materials performance issues that are to be resolved regarding the design and fabrication of the anode, the cathode, and the electrolyte of SOFCs. The cathode and the electrolyte are usually made from ceramics, while the anode is a composite consisting of metallic and ceramic particles. In such a composite anode, the metal particles serve to catalyze the oxidation of the fuel and to conduct the generated current. Ceramic particles are included to bond the anode to the ceramic electrolyte, prevent coarsening of the metal particles, and accommodate the thermal expansion mismatch between the metal particles and the electrolyte ceramics. One metal that has often been chosen for composite anodes is nickel, owing to its high melting temperature, good catalytic properties, and relatively low cost, (Ni). Conventionally, the nickel particles are embedded in yttria-stabilized zirconia (YSZ), although recently anodes based on doped ceria have become strong candidates for replacing YSZ. This development is driven by the superior of performance of metal–ceria anodes in both hydrogen and methane fuel streams, as well as in fuel streams containing H₂S, where metal?ceria anodes exhibit a higher tolerance for sulfur poisoning than the conventional metal-zirconia anodes.

The focus of our research is the microstructure of SOFC composite anodes and the changes they undergo during fuel cell operation. Using highly sophisticated methods of microcharacterization, including SEM (scanning electron microscopy), FIB (focused ion beam), and TEM (transmission electron microscopy) we have begun to gain important insight into the reactions that occur at these anodes and determine the lifetime of solid-oxide fuel cells [1].

Fig. 1. SEM image of a solid-oxide fuel cell anode.