Relaxation and polarization phenomena of phosphoric acid-doped [PBI4N(HfO2)x](H3PO4)y nanocomposite membranes for high-temperature proton-exchange membrane fuel cells are studied using Dynamic Mechanical Analysis (DMA) and Broadband Electrical Spectroscopy (BES). The membranes are obtained by casting combinations of a polybenzimidazole polymer (PBI4N) with increasing amounts of hafnium oxide nanofiller, resulting in [PBI4N(HfO2)x] hybrid systems with 0<0.32. Phosphoric acid at varying content levels (0-18 wt%) is used as a doping agent, giving rise to [PBI4N(HfO2)x](H3PO4)y membranes. DMA and BES studies lead us to determine that the electric response of the membranes is modulated by polarization phenomena and by a and b dielectric relaxation events of the polymer matrix. Additionally, the experimental results suggest that in [PBI4N(HfO2)x](H3PO4)y membranes the conductivity occurs owing to three conductivity pathways: two mechanisms involving inter-domain proton migration phenomena by “hopping” events; and one mechanism in which proton exchange occurs between delocalization bodies. These results highlight the significant effect of the hafnium oxide nanofiller content on the conductivity of [PBI4N(HfO2)x](H3PO4)y where, at x>0.04, demonstrates conductivity higher (9.0*10^2 S/cm) than that of pristine H3PO4-doped PBI4N (4.8*10^2 S/cm) at T>155 C.

Electric Response and Conductivity Mechanism in H3PO4-Doped Polybenzimidazole-4N-HfO2 Nanocomposite Membranes for High Temperature Fuel Cells

Nawn, Graeme;VEZZU', KETI;BERTASI, FEDERICO;PAGOT, GIOELE;PACE, GIUSEPPE;CONTI, FOSCA;NEGRO, ENRICO;DI NOTO, VITO
2017

Abstract

Relaxation and polarization phenomena of phosphoric acid-doped [PBI4N(HfO2)x](H3PO4)y nanocomposite membranes for high-temperature proton-exchange membrane fuel cells are studied using Dynamic Mechanical Analysis (DMA) and Broadband Electrical Spectroscopy (BES). The membranes are obtained by casting combinations of a polybenzimidazole polymer (PBI4N) with increasing amounts of hafnium oxide nanofiller, resulting in [PBI4N(HfO2)x] hybrid systems with 0<0.32. Phosphoric acid at varying content levels (0-18 wt%) is used as a doping agent, giving rise to [PBI4N(HfO2)x](H3PO4)y membranes. DMA and BES studies lead us to determine that the electric response of the membranes is modulated by polarization phenomena and by a and b dielectric relaxation events of the polymer matrix. Additionally, the experimental results suggest that in [PBI4N(HfO2)x](H3PO4)y membranes the conductivity occurs owing to three conductivity pathways: two mechanisms involving inter-domain proton migration phenomena by “hopping” events; and one mechanism in which proton exchange occurs between delocalization bodies. These results highlight the significant effect of the hafnium oxide nanofiller content on the conductivity of [PBI4N(HfO2)x](H3PO4)y where, at x>0.04, demonstrates conductivity higher (9.0*10^2 S/cm) than that of pristine H3PO4-doped PBI4N (4.8*10^2 S/cm) at T>155 C.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11577/3218963
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