Comprehensive Evaluation of Polymer Electrolyte Membrane (PEM) Using Thermal Analysis

Importance of the Topic

Proton exchange membrane fuel cells rely on thin polymeric membranes to conduct protons while separating reactant gases. Understanding the thermal and mechanical behavior of these membranes under varying hydration and temperature conditions is critical for ensuring reliable operation, optimizing performance, and preventing failure in applications ranging from automotive powertrains to stationary and portable energy devices.

Study Objectives and Overview

This study presents a systematic evaluation of a polymer electrolyte membrane (PEM) using a suite of thermal analysis techniques. By examining water melting, thermal decomposition, and mechanical response under controlled heating, the work aims to link material properties with operational performance limits and guide membrane design improvements.

Methodology and Instrumentation

The membrane was characterized with three complementary thermal instruments:

• DSC-60 (Differential Scanning Calorimetry) for detection of water melting transitions at different hydration levels
• DTG-60 (Thermogravimetric Analysis combined with Differential Thermal Analysis) for identifying decomposition stages and energy changes up to 600°C
• TMA-60 (Thermomechanical Analysis) for measuring dimensional changes and stress-strain behavior under tensile load up to 200°C

Main Results and Discussion

• Water Melting Behavior: At 6.7 % water content no endotherm was observed. At 8.5 % a single melting peak at –23.8 °C indicates clustered water. Above 12.6 %, two peaks emerge corresponding to bound water (around –31 °C) and free water (around –6 °C), with the free water peak shifting upward as hydration increases.
• Thermal Decomposition: TG-DTA reveals three mass-loss stages: dehydration up to 250 °C (≈6 % loss), sulfonic acid group cleavage near 316 °C, and main-chain breakdown around 409 °C, culminating in over 90 % total mass loss by 600 °C. Exothermic and endothermic events align with these transitions.
• Mechanical Response: Thermal expansion remains minimal until 87 °C, after which a steep increase is observed. Cyclic tensile tests at 60, 70, and 80 °C under 0–8 g load show growing hysteresis and reduced stress retention at higher temperatures, indicating diminished mechanical stiffness upon heating.

Benefits and Practical Applications

The combined data set offers actionable insights for optimizing membrane hydration to balance conductivity and mechanical integrity, predicting safe operating temperature limits, and selecting or modifying materials to enhance fuel cell durability. These findings support improved design guidelines for automotive, residential, and portable fuel cell systems.

Future Trends and Potential Applications

• Engineering of membranes with tailored hydrophilic domains or nanofillers to control water distribution and prevent ice formation during cold starts.
• Integration of advanced composite materials to boost thermal stability and mechanical resilience under dynamic loads.
• Development of in situ thermal and mechanical monitoring techniques to track membrane health during real-world operation.

Conclusion

Thermal analysis using DSC, TG-DTA, and TMA provides a comprehensive profile of PEM behavior across hydration levels and temperature ranges. The observed phase transitions, degradation pathways, and mechanical changes deliver vital information for improving membrane formulations and extending fuel cell service life.

References

Shimadzu Application News No. T143 Comprehensive Evaluation of Polymer Electrolyte Membrane Using Thermal Analysis