Clay–Carbon Nanotubes Hybrid Materials for Nanocomposite Membranes: Advantages of Branched Structure for Proton Transport under Low Humidity Conditions in PEMFCs

Abstract

A new class of hybrid materials based on carbon nanotubes (CNT) rooted on smectite clays (SWy) was synthesized by catalytic chemical vapor deposition (CCVD) method, and studied to be introduced in a perfluorosulfonic acid (Nafion) membrane. Side-wall chemical oxidation and organo-functionalization of the CNT was performed using organic ester molecules containing hydrophilic groups (−RSO3H). SWy–CNT nanoadditives were incorporated in the polymer by solution-precipitation method producing highly homogeneous nanocomposite membranes with outstanding mechanical properties. Materials were characterized by a combination of techniques (TGA, Raman, FT-IR, SEM, TEM, and DMA), while a deep investigation on the water transport properties was performed by NMR methods (PFG and relaxation times). Membranes containing SWy–oxCNT–RSO3H nanoadditives are able to guarantee a very high proton diffusion in “quasi-anhydrous” conditions. Proton mobility is ensured by a correct network created from the long nanotubes (well distributed through the clay nanoplatelets) appropriately functionalized with acid groups. Remarkable are the electrochemical results: the best membrane reaches conductivities of 7 × 10–2 S cm–1 at 120 °C and 30% RH, 1 order of magnitude higher than pristine polymer, and a rather high value in the current panorama of the PEMFCs.

Toward optimization of a robust low‐cost sulfonated‐polyethersulfone containing layered double hydroxide for PEM fuel cells

“…17,18,[27][28][29][30] It is therefore evident that the chemical and structural nature of the polymer, the chemical affinity and the nature of the interactions between the polymer chains and the material/filler play a crucial role in obtaining a homogeneous composite membrane characterized by a real nanodispersion. 17,18,[27][28][29][30] It is therefore evident that the chemical and structural nature of the polymer, the chemical affinity and the nature of the interactions between the polymer chains and the material/filler play a crucial role in obtaining a homogeneous composite membrane characterized by a real nanodispersion.…”

“…This kind of problem we never encountered with Nafion by preparing composite membranes with LDH or even layered fillers like nanoclays. 17,18,[27][28][29][30] It is therefore evident that the chemical and structural nature of the polymer, the chemical affinity and the nature of the interactions between the polymer chains and the material/filler play a crucial role in obtaining a homogeneous composite membrane characterized by a real nanodispersion.…”

Nano‐engineering of high‐performance PA6.6 nanocomposites by the integration of CVD‐grown carbon fiber on graphene as a bicomponent reinforcement by melt‐compounding

“…In one of the studies, Simari et al . grew CNT on clay in the presence of Fe and Ni catalysts by CVD technique and dispersed clay‐CNT hybrid materials in Nafion solution to prepare polymer electrolyte membrane for fuel cells . In another work, Fan et al .…”

Advanced nanocomposite membranes for fuel cell applications: a comprehensive review

“…The monovalent ions located between the clay layers are used for the modification allowing the absorption of polar solvents such as water (Kim et al, 2015a). Recently, organo-functionalization of CNT was grafted on smectite clays (SWy) by catalytic chemical vapour deposition (CCVD) method (Simari et al, 2016) (Fig. 10), and their composite membranes with Nafion ® matrix exhibited 7 × 10 -2 S cm -1 proton conductivity at 120 °C and 30% RH.…”