Noninvasive temperature sensing technologies and the role of ferromagnetic nanoparticles in future applications.

In polymer electrolyte fuel cells (PEFCs), temperature gradients can exert a substantial influence on cell performance and durability. Monitoring these gradients without perturbing fuel cell operation is one of the main challenges. This study introduces a novel method for remotely mapping fuel cell temperature using ferromagnetic nanoparticles, such as nickel and iron. These nanomediators possess temperature-dependent magnetic properties, enabling neutron depolarization imaging (NDI) to provide insights into the internal fuel cell temperature. We extensively evaluated the main parameters pertaining to the utilization of these nanoparticles in powdered form for temperature sensing. This encompassed an assessment of the minimum detection concentration and temperature sensitivity. Our findings reveal that while the smallest nanoparticles yield the highest relative change in depolarization, they exhibit considerably lower absolute depolarization coefficients. Hence, larger particles emerge as strong candidates for signal detection. Despite the challenges posed by the considerable size of these sensors, which inhibits in-situ dispersion, there is an opportunity to enhance nanoparticle characteristics. Such improvements could be achieved by scaling up the size of the materials from the nanoscale while retaining high magnetic saturation and temperature sensitivity.