NETL researchers are exploring how heterogeneity, or a lack of uniform structure and composition, on a microscopic level can affect the performance of solid oxide fuel cell (SOFC) components. SOFCs, which, like batteries, create electricity directly through electrochemical reactions, are extremely efficient, require minimal water consumption and generate almost no emissions; however, SOFCs face issues with reliability, durability and cost. NETL researchers are working to overcome these problems by studying what effect heterogeneity has on fuel cell degradation, helping to clear the way to commercial development.
On a basic level, the electrochemical reactions that generate the electrical current happen at its electrodes (like the positive and negative electrodes on a battery). The electrodes are comprised of a mixture of different catalyst materials and gas pores (the gases fed to the electrodes undergo the electrochemical reactions). Researchers are looking at these electrodes with powerful microscopes and using advanced 3D imaging techniques to reveal their microstructures, which can range from being uniform, or homogenous, in structure and composition in ideally-made fuel cells to more heterogeneous in the more mass-produced, low-cost fuel cells.
“From our research, it appears that this heterogeneity in the microstructure of the more common commercial fuel cells creates problems like efficiency reductions and zones of poor performance,” said Billy Epting, who works on the NETL research team as part of the Lab’s Postgraduate Research Program. “These types of issues can negatively impact fuel cell reliability and durability, which creates a major hurdle for commercialization.”
NETL researchers are working with SOFC industrial partners to discover which steps in the mass production process leads to this heterogeneity and whether the costs associated with making a less heterogeneous cell will be offset by the cost savings of making a better performing, longer-lasting cell. To do this, they create high-resolution 3D reconstructions of small sections of real SOFC electrodes to relate their microstructures to their experimentally-measured performances. They then compare these results to those from synthetic microstructures rendered using computer simulations.
“When we compare the real microstructures to the computer-generated microstructures, we see that a couple of factors come into play,” said Epting. “First of all, we see a difference in particle size distributions in the commercial fuel cells. These variations are largely unavoidable because the feedstock powders used to make the fuel cell generally have a variation in their particle size. However, it appears that poor mixing of the feedstock (during cell fabrication) contributes more significantly to heterogeneity in the microstructure.”
While this research is ongoing, methods used by the NETL researchers are improving the understanding of the performance of complex electrodes and forging a new path to accelerate the development of reliable, durable, low-cost SOFCs capable of efficiently powering the nation while protecting the environment.
Photo caption: The commercial solid oxide fuel cell cathode image seen here was created by recontructing stacks of images captured by a powerful microsope with 3D imaging software. A more ideal cathode would have an even distribution of the multiple materials (the different colored features in the image). Having large clumps of one material in some areas decreases the cell performance and lifetime.