A Study On Nafion Composite Membranes For High Temperature Proton Exchange Membrane Fuel Cell

PEMFC has been considered as an alternative power source for electric vehicles, because of its high efficiency, high power density, rapid start-up, and low or zero emissions. The development and application of PEMFC are restricted by several major technologic barriers. For example the proton conductivity of the present proton exchange membrane is low under low relative humidity at higher temperature. In this study, we attempte to develope high temperature proton exchange membranes which can be work at low relative humidity.Nafion membrane has been widely used in PEMFC. However, due to the dehydration at high temperature (>100℃), the proton conductivity of Nafion membrane drops drastically, which results in obvious drop in FC performance .To tackle this prob, we intend to embed nanoscaled SiO₂ and TiO₂ particles with good water-retention into Nafion membrane.We prepared Nafion/ TiO₂ composite membranes and Nafion/ SiO₂ composite membranes with various TiO₂ or SiO₂ content, and we tested their mechanical strength , dimensional stability and proton conductivity. Results show that, the mechanical strength and their dimensional stability are enhanced, when the content of TiO₂ nano particles is 3wt%, the tensile strength increased by 19.5%. And the swelling is reduced with morer embedment of TiO₂ or SiO₂ particles, also, the proton conductivity of Nafion/ TiO₂ composite membranes under low relative humidity at high temperature(120℃) is improved. When the content of TiO₂ nano particles is 4wt% and the relative humidity is 45%, the proton conductivity of composite membrane is almost twice larger as Nafion membrane.The incorporation of SiO₂ with Nafion results in improved mechanical strength , hydrogen permeability and their dimensional stability . When the content of SiO₂ nano particles is 7wt%, the hydrogen permeability is 1.7921×10-12mol/(Kpa.cm.min),which is twice lower than Nafion membrane. The proton conductivity under low relative humidity at high temperature(120℃) is also enhanced with the embedment of TiO₂ or SiO₂ nano particles in Nafion membrane. When the content of SiO₂ nano particles is 4wt% and the relative humidity is 55%, the proton conductivity of composite membrane is 0.05 S·cm-1,which is twice larger as Nafion membrane.