Sandwich structure SPPO/BPPO proton exchange membranes for fuel cells: Morphology–electrochemical properties relationship

• Sandwich structured SPPO/ BPPO/SPPO membrane is reported.
• Sandwich structured exhibit self-humidifying ability up to ca. 120°.
• The membranes exhibit both high proton conductivity and selectivity.

Sandwich structure composite membranes based on sulfonated and brominated poly (2, 6-dimethyl-1,4-phenylene oxide) were prepared through a layer-by-layer deposition method. The adhesion between layers was enhanced via surface modification with ammonia solution. The morphology and electrochemical property relationships of resulting membranes were studied by coupling SEM sectional image, Fourier transform infrared spectroscopy (FTIR) and measuring the water uptake behavior, ion-exchange capacity, proton conductivity and methanol permeability. The obtained membranes were also characterized by the thermogravimetric analysis (TGA). Interestingly, the three-layered membranes significantly showed increased proton conductivity at low humidity as well as reduced water uptake and low methanol permeability compared with that of the pristine SPPO membranes. The proton conductivity of three-layered composite membrane was 0.109 S/cm, whereas the plain SPPO membrane showed a 0.1 S/cm at 80 °C with low relative humidity of 50%. The calculation of membrane selectivity indicates that the three-layered membranes are a promising candidate for direct methanol fuel cell (DMFC) at low humidity and intermediate temperature. Moreover, the sandwich structure composite membranes exhibited a self-humidifying ability at high temperature (ca. 120 °C). The sandwich structured membranes exhibited superior fuel cell performance than pristine SPPO membrane.

Layer by layer deposition techniques through solution casting are used to prepare three layers membrane composed with SPPO, outer layers and BPPO, central layer to obtain a self-humidifying proton exchange membrane with high selectivity. Interlayer surface separation is prevented by surface functionalization of each supporting layer with ammonia. The proton conduction through central layer is more governed by Grotthus mechanism that gives membrane good proton conductivity at reduced humidity. The superior proton conductivity and self-humidifying ability of this membrane at low relative humidity can be useful for DMFC application. Figure optionsDownload high-quality image (141 K)Download as PowerPoint slide