Polyelectrolyte Nanocomposite Membranes Using Surface Modified Nanosilica for Fuel Cell Applications

Surface modified multi‐walled carbon nanotubes and Nafion nanocomposite membranes for use in fuel cell applications

“…Generally speaking, 2 principle mechanisms, Vehicle and Grotthuss (hopping), describe proton diffusion through the membrane. In the vehicle mechanism free water takes part in diffusion of hydronium ions, while Grotthuss‐type transfer is related to the proton hopping from one proton‐conducting site to a neighboring one with the aid of hydrogen‐bond networks . The proton conductivities of the membranes containing MWCNT‐SO 3 H or MWCNT‐Im were higher than those of the membrane containing MWCNT‐OH and Nafion 117 at all temperatures.…”

“…As reported in some previously published papers, the morphological study of Nafion shows that this polymer is made up of 2 nanoscopic separated phases, including hydrophilic sulfonic acid groups and the hydrophobic fluorinated backbones. Considering this, the presence of hydrophilic nanochannels, consist of sulfonic acid groups (the proton‐conducting sites), because of the amphiphilic feature between hydrophobic fluorinated backbones and hydrophilic pendant side chains, the second strategy, rather than using an alternative polymer system, is related to modifying the nanosized microstructure of Nafion by incorporating different types of organic or inorganic additives . Adding inorganic nanofillers into the PEMs, such as inorganic oxides (for example, TiO 2 or SiO 2 ), carbon nanotubes (CNTs), modified and unmodified nanoclays, and zeolite result in a considerable reduction in methanol permeability by modifying the proton transport nanochannels and introducing tortuous proton‐conducting pathways, as a consequence of dispersing inorganic fillers into the PEM matrix and achieving the nanocomposite membranes.…”

“…In this regard, Tohidian et al, Asgari et al, and Sung et al investigated the pristine, as well as the functionalized nanomaterials with imidazole‐containing residues as an alternative way to localize these proton‐conducting sites to manufacture new nanocomposite PEMs that had an acceptable proton conductivity, and also low methanol permeability due to incorporating the imidazole groups, as the proton‐conducting sites to the system. In addition, some researches were devoted to show the role of sulfonic acid groups functionalized nanofillers with in the nanocomposite PEMs . It is believed that, in comparison to the nanocomposite PEMs containing pristine nanofillers, because of the decrease in the activation energy of proton hopping via the ─SO 3 H derivatives, immobilizes on the surface of the modified nanofillers, the proton conductivity of the membranes is increased.…”

“…In addition, some researches were devoted to show the role of sulfonic acid groups functionalized nanofillers with in the nanocomposite PEMs. 4,[11][12][13]24 It is believed that, in comparison to the nanocomposite PEMs containing pristine nanofillers, because of the decrease in the activation energy of proton hopping via the ─SO 3 H derivatives, immobilizes on the surface of the modified nanofillers, the proton conductivity of the membranes is increased.…”

Prospects of Membrane Science Development

“…First of all, imparting acidic properties to them is of interest. Nafion membranes containing silica nanoparticles with grafted sulfo groups or sulfonic acid fragments [69,70] exhibited increased proton conductivity and low methanol permeability. It turned out to be possible to substantially decrease the methanol permeability by doping Nafion membranes with metal oxides, silica, and phosphotungstic acid [71,72].…”