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| Hauptseite > Publikationsdatenbank > Crystal formation with fractal size distribution of ABPBI membranesin high temperature polyelectrolyte fuel cells |
| Hauptseite > Publikationsdatenbank > Crystal formation with fractal size distribution of ABPBI membranesin high temperature polyelectrolyte fuel cells |
| Conference Presentation (Other) | FZJ-2016-01016 |
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2015
Abstract: Many different polymeric materials are investigated in terms of their usability in polymer electrolyte fuel cells (PEFC). One of the most promising classes of PEFC are high temperature polymer electrolyte fuel cells (HT-PEFC) operating at elevated temperatures between 160 – 180 °C. In contrast to the PEFC, operating at temperatures below 100°C (Nafion® being one of the most common polyelectrolyte material used), HT-PEFC provide many advantages such as significantly simplified water management and improved CO tolerance, which enables a wide range of applications in medium power range (~5 kW). The core of the PEFC - proton conducting polyelectrolyte membrane, which separates two electrodes in a fuel cell and acts as a proton conductor. Since the high operation temperatures require polymers with excellent thermal and chemical stability, commercially available poly(2,5-benzimidazole) (ABPBI) membrane attract particular interest. Its aromatic backbone provides an excellent thermal stability, high glass transition temperature and good chemical resistance, but does not provide any intrinsic proton conductivity. Owing to the basic nature of ABPBI it can be impregnated with a high amount of phosphoric acid (PA), which is known to have the highest intrinsic proton conductivity and thus assures high protonic conductivity of the impregnated membrane. Since such proton conducting membrane allows proton transport and prevents the crossover of gases and electrons, its structural and transport properties are of crucial importance for physical and electrical properties of the PEFC. The structural properties of proton conducting poly(2,5-benzimidazole) (ABPBI) membrane in its pristine as well as phosphoric acid (PA) doped form have been investigated with small angle neutron- and X-ray scattering (SANS and SAXS respectively), X-ray diffraction (XRD), polarised light- and transmission electron microscopy (TEM). Obtained results are linked to the proton diffusion in a phosphoric acid doped ABPBI membrane measured with pulsed-field gradient-nuclear magnetic resonance (PFG NMR) technique. Our investigation demonstrates formation of crystalline regions in the ABPBI membrane with fractal size distribution ranging from small (TEM) to large (optical microscopy) length scales.
Keyword(s): Energy (1st) ; Soft Condensed Matter (2nd) ; Materials Science (2nd)
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