On the main factors limiting the performance of state-of-the-art polymer electrolyte membrane fuel cells in the 90–100 °C temperature range

This study investigates the performance limitations of state-of-the-art PEMFC operating in the 90-100 °C temperature range under low to moderate RH conditions, i.e . close to those encountered in automotive applications. Using a commercial MEA based on a 12 µm thick LSC-PFSA membrane, a comprehensive performance mapping was conducted across various operating parameters including temperature, pressure, RH, and air stoichiometry. Results show that elevated temperature negatively impacts performance, especially at high current densities, primarily due to MEA dehydration. Electrochemical Impedance Spectroscopy (EIS) revealed that the cell high-frequency resistance (R hf ) increases sharply with current density at high temperatures, highlighting hydration as a dominant limiting factor. Accelerated stress tests confirmed that heat generation was the primary driver of MEA dehydration under these conditions, rather than electro-osmotic drag. While increasing gas RH improves hydration and performance, a threshold (∼40% RH) was identified, beyond which gains are offset by increased oxygen dilution and mass transport limitations. iR-corrected polarization curves also showed residual voltage losses at high temperatures, attributed to reduced oxygen partial pressure due to increased water vapor content. Impedance spectra confirmed no significant increase in mass transport resistance at high temperature, suggesting that oxygen dilution and MEA dehydration are the primary causes of performance degradation. These findings underscore the critical importance of water management at elevated temperatures and provide a foundation for future work on optimized materials and operating strategies for intermediate temperature PEMFC.