Inorganic-organic membranes based on Nafion, [(ZrO₂)路(HfO₂)_0.25] and [(SiO₂)路(HfO₂)_0.28] nanoparticles. Part II: Relaxations and conductivity mechanism

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• 作者：Vito Di Noto^a ; ¹ ; ^{vito.dinoto@unipd.it} ; Nicola Boaretto^a ; Enrico Negro^a ; Phil. E. Stallworth^b ; Sandra Lavina^a ; Guinevere A. Giffin^a ; Steve G. Greenbaum^b
• 关键词：Hybrid inorganic&ndash ; organic proton-conducting membranes ; Nafion ; Polymer electrolyte membrane fuel cells ; Dynamical mechanic analysis ; Pulse-field-gradient spin-echo NMR ; Broadband electric spectroscopy
• 刊名：International Journal of Hydrogen Energy
• 出版年：2012
• 期刊代码：42_03603199
• 类别：ch
• 出版时间：April, 2012
• 卷：37
• 期：7
• 页码：6215-6227
• 文件大小：1525 K

摘要

Two classes of hybrid inorganic-organic proton-conducting membranes consisting of Nafion and either [(ZrO₂)路(HfO₂)_0.25] or [(SiO₂)路(HfO₂)_0.28] nanofiller are investigated to elucidate their relaxations and conductivity mechanism and are labeled [Nafion/(ZrHf)_x] and [Nafion/(SiHf)_x], respectively. The membranes are studied by dynamic mechanic analysis (DMA) and broadband electric spectroscopy (BES). The latter technique allows a determination of the direct current ionic conductivity (蟽_DC) and the proton diffusion coefficient . Pulse-field-gradient spin-echo nuclear magnetic resonance experiments (PFGSE-NMR) are carried out to determine the water self-diffusion coefficients . and are correlated to obtain insight on the conductivity mechanism of the proposed materials. Results indicate that the nanofiller particles play a major role in the proton conduction mechanism of the proposed materials. It is demonstrated that the basic [(ZrO₂)路(HfO₂)_0.25] nanoparticles form Nafion-nanofiller dynamic cross-links with high ionic character. These cross-links improve the mechanical properties and enhance the overall proton conductivity of the membranes at low humidification levels owing to an efficient delocalization of the protons. In [Nafion/(SiHf)_x] membranes, the dynamic cross-links occur due to dipole-dipole interactions between the side groups of the Nafion host polymer and the quasi-neutral [(SiO₂)路(HfO₂)_0.28] nanoparticles. These cross-links significantly reduce the delocalization of the protons, which decreases the overall conductivity of materials.