Application of FTIR in direct methanol fuel cells – Quantitative analysis of PTFE in gas diffusion layers

•PTFE contents in GDLs were quantitatively investigated by FTIR-DR & ATR.•DR method takes advantages in sensitivity, range and precision over ATR method.•By DR method, we observe that PTFE in MPLs migrates to BLs during the aging test.

Gas diffusion layers (GDLs) of direct methanol fuel cells (DMFCs), consisting of a microporous layer (MPL) and a back layer (BL), influence the cell performance and stability significantly due to the critical function that the GDL undertook, i.e., distribution of reactants and removal of the products in electrodes. The hydrophilic/hydrophobic properties of the GDLs are required to tailor to the transport/transfer of reactants/products depending on a specific electrode reaction. One important way to adjust the hydrophobic/hydrophilic properties of GDLs is to vary PTFE content in GDLs. In this paper, we employ infrared spectroscopy technique, specifically, diffuse reflection (DR) method and attenuation total reflection (ATR) method, to determine the PTFE content in both MPLs and BLs quantitatively by comparing the measured C-F intensity with the pre-calibrated standard plots. Compared to the ATR method, the DR method takes advantages of sensitivity, wide range and precision. By the DR method, we succeed in observing that PTFE in MPLs migrates to BLs, consistent with the corresponding EDX results for a sample experienced 600 h lifetime test, suggesting DR method an effective approach to determine quantitatively the hydrophilic/hydrophobic properties of both MPLs and BLs.