Nanostructured Anodes for Low Temperature Solid Oxide Fuel Cells
Elizabeth Miller, Northwestern University
Solid oxide fuel cells (SOFCs) are high-temperature energy conversion devices that transform chemical energy directly into electrical energy, making them an efficient alternative to fossil fuel-based energy sources. Lowering operating temperatures of SOFCs from the current 750-800 °C to less than 650 °C is of interest to reduce balance of plant costs, prevent interconnect and seal material issues, decrease start-up times, and improve long-term device durability. Much of the work on low-temperature cells is based on strontium- and magnesium-doped lanthanum gallate (LSGM), an electrolyte material with high ionic conductivity at reduced temperature. However, because of its reactivity with Ni, it cannot simply be used as an exact substitute with current Ni-yttria stabilized zirconia anodes. Therefore, alternative anode materials such as perovskites or unconventional fabrication techniques such as nano-infiltration must be used.
Here we present work on La0.9Sr0.1Ga0.8Mg0.2O3-δ electrolyte cells with novel anodes including Sr0.8La0.2TiO3 (SLT) infiltrated with nickel, SrTi0.3Fe0.7O3 (STF) Ni-free anodes, and catalytic oxide anodes substituted with Ru or Pd. SLT anode-supported button cells were fabricated, electrochemically characterized, and examined with scanning electron microscopy (SEM) to determine Ni-coarsening behavior during operation for short-term and long-term tests. Addition of an LSGM functional layer, which increases the electrochemically active triple phase boundary (TPB) region, was found to yield power densities greater than 1 W/cm², and the interaction between LSGM and Ni in the functional layer was found to affect performance. STF powders were synthesized using sol-gel and solid state reaction methods, then heat-treated and characterized to determine appropriate calcination temperatures. Optimally sized powders were used to create highly active nanoscale anodes in LSGM electrolyte-supported cells. Exsolved Ru and Pd nanoparticles were examined using transmission electron microscopy (TEM), electron tomography, and in situ X-ray diffraction (XRD) to study nanoparticle evolution with time and to determine nanoparticle morphology on the oxide matrix surface.
Abstract Author(s): Elizabeth C. Miller, Scott A. Barnett