Raman Microspectroscopy as a Useful Tool for In Situ and Operando Studies of Water Transport in Perfluorosulfonic Membranes for PEMFCs

Abstract An operating PEMFC for commercial use must be able to adapt to variations in power demands and operating conditions while maintaining near optimal performance. Current research shows that one of the main issues affecting power output, stability, and longevity is the quantity and distribution of water in the system. The last are strongly affected by the sorption and transport properties of the polymer electrolyte. Thus, the need for a fundamental understanding of water transport in the PEMFC membrane‐electrode assembly has motivated, over the past few years, the development of new operando diagnostic tools sensitive to the membrane hydration. Among these, the most recent technique is based on confocal Raman microspectroscopy. This tutorial review is devoted to the illustration of the basis of this method, with a particular focus on the Raman signal processing needed to obtain reliable through‐plane water concentration profiles across PFSA membranes. Then, the potential of in situ and operando μ‐Raman is highlighted by reviewing the few studies reported to date, completed by the most recent results obtained by our group. Finally, advantages and drawbacks of operando Raman microspectroscopy are shortly discussed.