Decoding Pt-electrolyte-ionomer interactions during the oxygen reduction reaction via operando FTIR.

Operando Fourier transform infrared (FTIR) spectroscopy is a powerful technique for investigating the electrocatalytic interface during the oxygen reduction reaction (ORR). This review summarizes the technical challenges and recent developments in applying operando FTIR to the Pt/electrolyte and Pt/ionomer interfaces. The different optical configurations are discussed, and the specific material requirements for internal reflection elements and enhancement layers are outlined. Afterwards, the spectral interpretation of key interactions is carefully examined, distinguishing between reaction intermediates and signals arising from the electrolyte. Particular attention is given to the interactions at the Pt-Nafion interface, where we discuss the identification of vibrational bands related to sulfonate groups and hydration networks. Finally, this review highlights how distinguishing these signals is essential for understanding the mechanisms that govern catalyst activity and durability in fuel cells.