2 research outputs found
ClayâCarbon Nanotubes Hybrid Materials for Nanocomposite Membranes: Advantages of Branched Structure for Proton Transport under Low Humidity Conditions in PEMFCs
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 (âRSO<sub>3</sub>H). SWyâCNT 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 SWyâoxCNTâRSO<sub>3</sub>H nanoadditives are able to guarantee a very high proton diffusion
in âquasi-anhydrousâ 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 Ă 10<sup>â2</sup> S cm<sup>â1</sup> 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
Ion Dynamics and Mechanical Properties of Sulfonated Polybenzimidazole Membranes for High-Temperature Proton Exchange Membrane Fuel Cells
Polybenzimidazole (PBI)-based membranes
are one of the systems
of choice for polymer electrolyte fuel cells. Monomer sulphonation
is one of the strategies suggested to improve proton transport in
these membranes. We report a NMR and dynamic mechanical study aiming
to investigate the effect of the sulphonation on the proton dynamics
and the mechanical properties of the membranes. The analyses of <sup>1</sup>H self-diffusion coefficients and <sup>1</sup>H and <sup>31</sup>P spectra versus temperature show that sulphonation causes the formation
of interchain cross-links, which involve phosphoric acid molecules
and the sulfonic groups. This, in turn, reduces the proton mobility
and, consequently, the ionic conductivity. The increase of the membrane
stiffness with sulphonation is confirmed by dynamic mechanical analysis
through the behavior of the storage modulus