Solid oxide fuel cells (SOFCs) hold great promise for providing highly efficient, clean energy for a low-carbon economy. However, adoption of these next-generation technologies hinges on reducing component degradation and improving longevity.

The ability to make numerous, real-time, highly accurate temperature measurements across an SOFC could better inform SOFC modeling efforts aimed at designing more resilient fuel cells. To this end, NETL researchers, in collaboration with the University of Pittsburgh, have successfully embedded multiple distributed fiber optic sensors into an SOFC multi-cell test to achieve a previously unattainable degree of spatial resolution in temperature measurement. The work was recently featured in an article in the prestigious journal Applied Energy.

“Distributed fiber optic sensors offer many advantages over traditional thermocouple measurement technologies,” NETL’s Mike Buric, Ph.D., said. “For example, because these distributed fiber optic sensors can obtain measurements all along their length, we were able to generate at least 48 individual temperature measurements for each electrode using only five embedded fiber optical sensors. The same number of measurements would require 48 individual thermocouples, which just isn’t viable, considering installing even just a few thermocouples is typically regarded as novel and extensive.”

The fiber optic sensors, which were hardened for use in a high temperature environment and embedded into the current collector plates of a 25 cm² planar SOFC through additive manufacturing, provided temperature measurements with 4-mm spatial resolution, meaning temperature could be measured every 4 mm along the fiber. Additionally, the sensors demonstrated the capability of detecting temperature gradients of less than 5 degrees Celsius when different amounts and compositions of hydrogen fuel were added.

“In addition to the high spatial resolution, the sensitivity we achieved was also promising,” Buric said. “Multiphysics SOFC modeling simulations showed agreement with these experimental results. Simulations and experiments of larger, more industrially relevant planar SOFCs show that they can experience temperature difference on the order of 50-100 degrees Celsius, so our sensor is more than sensitive enough for large SOFC stacks.”

Understanding where and why these temperature gradients are occurring is crucial for designing systems that can resist degradation caused by thermal stresses and other issues. The combination of high spatial resolution data harnessed by distributed fiber sensors and reliable computational models can be used to re-design and optimize the structural parameters of fuel and air channels, including geometry, channel depth, width, and thickness of component layers to reduce such temperature gradients.

“To our knowledge, this work represents the first viable, real-time system for mapping the temperature distribution inside an operating SOFC that has achieved sub-centimeter-scale resolution,” said Sydni Credle, Ph.D., technology manager for NETL’s Crosscutting Research Sensors and Controls Program, which funded development of the optical fiber sensor and associated distributed measurement techniques. 

The demonstration took place at NETL’s fuel cell testing facility at its Morgantown, West Virginia, research site and was funded through the Solid Oxide Fuel Cell Program. 

The U.S. Department of Energy’s National Energy Technology Laboratory develops and commercializes advanced technologies that provide clean energy while safeguarding the environment. NETL’s work supports DOE’s mission to ensure America’s security and prosperity by addressing its energy and environmental challenges through transformative science and technology solutions.