Solid oxide fuel cells (SOFCs), a promising technology that can efficiently produce energy using fossil fuels with no moving parts and low emissions, present a particularly perplexing economic challenge: current systems operate at maximum efficiency between 700 and 1000 degrees Celsius, but such high temperatures shorten their service life, requiring more frequent fuel cell stack replacements. Lowering the operating temperature makes them last longer, but requires additional cells in the stack to deliver the same performance, and that drives up costs.
Researchers at the National Energy Technology Laboratory (NETL) are searching for answers to create SOFCs that can effectively operate at lower temperatures with a longer life-span by taking a deep look inside fuel cells on a microstructural level.
Fuel cells are electrochemical devices that rely on their components’ catalytic activity and conductivity to produce electricity. Changes happening in the microstructure can have big impacts on how well a cell performs. NETL modeling work is providing a detailed look at how SOFCs function over time under specific operating conditions and a better understanding of how these ultra-clean, ultra-efficient coal-to-electricity devices can be made more durable, economical, and commercially successful.
When investigating what factors could contribute most to improving the economics of SOFCs, and thereby enhance their commercial success, NETL systems analysis experts identified degradation as a key issue. Degradation is a continuous loss of performance over time. In SOFCs, degradation can manifest in different ways, but the end results are changes to the cell’s active regions (where reactions occur) and reduced longevity.
Investigating degradation requires a detailed picture of the SOFC microstructure, and getting a useful representation of the microstructure on the nanometer scale is an integrated research effort within the NETL SOFC group. The program involves modeling and sample analysis from the atomic scale all the way up to full-scale commercial systems.
The SOFC program’s microstructural visualization work begins at Carnegie Mellon University, where NETL research partners use powerful microscopy equipment, such as focused-ion-beam scanning electron microscopes (FIB-SEM), to capture cross-section images of actual fuel cells from NETL industry partners. With this data, SOFC researchers produce high-resolution, three-dimensional reconstructions.
NETL has created the largest high-resolution electrode reconstructions in the world—some are 100 times larger than any other visualization efforts at the same resolution. Using these unique reconstructions, researchers examine the inner workings of the SOFC and quantify changes to an SOFC’s active regions over time. Modeling allows researchers to simulate the SOFC aging process and obtain meaningful results faster and more economically than operating SOFCs for tens of thousands of hours.
Modeling also allows researchers to measure changes and study how specific parameters, such as surface area and particle size distributions, affect cell performance. Coupled with the information gained from 3D microstructure visualization, researchers can determine what operating conditions and microstructures will be most favorable for a given cell, leading to a longer, more productive cell lifespan.
While adjustment of operating conditions to prolong cell life is one approach, a second modeling effort at NETL examines SOFC properties to determine how the cell itself may be optimized for greater durability. In this effort, researchers use simulations of synthetic SOFCs to get a better idea of what constitutes the perfect fuel cell. Simulations offer the advantage of being faster and more precise than making physical lab samples. With simulations, NETL researchers design and test various theoretical microstructure configurations and materials that could not be readily constructed and tested without considerable other engineering efforts. They then draw conclusions about which aspects of a cell to target to boost performance and lifetime.