An Ultrathin Water Retentive TiO 2 Composite Interfacial Layer for Enhanced Low Humidity PEMFC Operation

Abstract Operating polymer electrolyte membrane fuel cells (PEMFCs) at low relative humidity (RH) can simplify external humidification and reduce flooding, but membrane dehydration increases ohmic losses. We applied an ultrathin, water retentive composite interfacial layer containing titanium dioxide (TiO 2 ), carbon black, and polytetrafluoroethylene (PTFE) to the microporous layer (MPL) of commercial gas diffusion layers (GDLs) by ultrasonic spraying at controlled TiO 2 mass loadings of 0, 0.05, 0.10, 0.20, and 0.30 mg cm −2 . Increasing loading reduced the contact angle; the through plane gas permeability fell to roughly 40% of baseline by 0.10 mg cm −2 , while loadings above 0.10 mg cm −2 further thickened the MPL, raised its electrical resistance, and formed a quasi continuous surface crust. At 30% RH, the 0.05 mg cm −2 loading performed best among those evaluated in single cell tests, raising peak power density from approximately 590 mW cm −2 to 800 mW cm −2 . Electrochemical impedance spectroscopy (EIS) showed that the high frequency resistance (HFR) decreased from 132 mΩ cm 2 to 93.6 mΩ cm 2 . At high RH, the modification reduced peak power and enlarged the low frequency impedance response. These results support using the composite layer in PEMFC systems operating predominantly at low humidity.