An Ultrathin Self-Humidifying Membrane for PEM Fuel Cell Application:  Fabrication, Characterization, and Experimental Analysis

An ultrathin poly(tetrafluoroethylene) (PTFE)-reinforced multilayer self-humidifying composite membrane (20 μm, thick) is developed. The membrane is composed of Nafion-impregnated porous PTFE composite as the central layer, and SiO2 supported nanosized Pt particles (Pt−SiO2) imbedded into the Nafion as the two side layers. The proton exchange membrane (PEM) fuel cell employing the self-humidifying membrane (Pt−SiO2/NP) turns out a peak power density of 1.40 W cm-2 and an open circuit voltage (OCV) of 1.032 V under dry H2/O2 condition. The excellent performance is attributed to the combined result of both the accelerated water back-diffusion in the thin membrane and the adsorbing/releasing water properties of the Pt−SiO2 catalyst in the side layers. Moreover, the inclusion of the hygroscopic Pt−SiO2 catalyst inside the membrane results in an enhanced anode self-humidification capability and also the decreased cathode polarization (accordingly an improved cell OCV). Several techniques, such as transmission electronic microscopy, scanning electronic microscopy, energy dispersive spectroscopy, thermal analysis and electrochemical impedance spectroscopy etc., are employed to characterize the Pt−SiO2/NP membrane. The results are discussed in comparison with the plain Nafion/PTFE membrane (NP). It is established that the reverse net water drag (from the cathode to the anode) across the Pt−SiO2/NP membrane reaches 0.16 H2O/H+. This implies a good hydration of the Pt−SiO2/NP membrane and thus ensures an excellent PEM fuel cell performance under self-humidification operation.