MOSFET-Amplified Fluoride Ion Sensor for Real-Time Monitoring of Nafion® Membrane Degradation in PEM Fuel Cells

Real-time monitoring of membrane degradation is critical for enhancing the durability and reliability of proton exchange membrane fuel cells (PEMFCs). Chemical degradation of the Nafion® membrane results in the release of fluoride ions (F⁻), making F⁻ concentration a direct and quantifiable indicator of membrane health. This study presents a fluoride ion sensing system capable of continuous, in situ detection using a LaF₃ crystal-based ion-selective membrane paired with an Ag/AgCl reference electrode and integrated with a low-threshold metal-oxide semiconductor field-effect transistor (MOSFET) for signal amplification. A miniaturized bipotentiostat was used to measure voltage and current outputs, enabling high-resolution tracking of dynamic fluoride ion fluctuations. Both a commercially available sensor and a lab-fabricated LaF₃-based sensor demonstrated stable, reversible, and sensitive responses across a wide concentration range. The system effectively captured real-time changes in F⁻ concentration associated with membrane degradation, validating its suitability for operando diagnostics. The compact design, low power requirements, and consistent performance of the sensor support its potential for miniaturization and direct integration into PEMFC stacks. Such embedded monitoring would enable continuous, non-invasive assessment of membrane condition, early detection of degradation, and predictive maintenance, ultimately extending fuel cell service life and operational efficiency.