Table 3.
Functionalization method of CNT via different reagents, and representative PEM properties of corresponding composite membranes.
| Composite Membrane (Matrix/Filler) |
Filler Content (wt. %) |
Functionalization of CNTs | Water Uptake a (%) |
IEC b (meq g−1) |
Proton Conductivity c (mS cm−1) | Ref. | ||
|---|---|---|---|---|---|---|---|---|
| Reagent | Method | 20% RH | 80% RH | |||||
| Nafion/CNT | 5.0 | - | - | 20.7 | 0.8 | 1.0 | 40.0 | [53] |
| Nafion/sMWCNT d | 0.25 | 4-benzendiazonium sulfonic acid |
Grafting | 29.3 | - | 2.3 (60 °C) |
198 (60 °C) |
[76] |
| Nafion/MWCNT-SO3H e | 0.5 | 1,3-propanesultone | 34.5 | 0.9 | - | 150 | [77] | |
| Nafion/MWCNT-Im f | 0.5 | 4-imidazolecarboxylic acid | Dehydration reaction |
28.0 | 0.9 | - | 210 | [77] |
| SPEEK/CNT | 1.5 | - | - | - | 2.8 | 47.0 | [79] | |
| SPAES/HNT g | 1.0 | SPAES 100 hydrophilic oligomer |
Nucleophilic substitution | 58.0 | - | 0.7 | 237 (100% RH) |
[78] |
| SPEEK/ACNT h | 1.5 | 3-aminopropyl triethoxysilane |
Condensation reaction | 17.5 | 1.2 | 7.3 | 115 | [79] |
a Measured at room temperature. b Determined by titration at 25 °C. c Proton conductivity at 80 °C. d,e Sulfonic acid group grafted multi-walled carbon nanotube. f Imidazole group grafted multi-walled carbon nanotube. g Sulfonated poly(arylene ether sulfone) hydrophilic oligomer grafted carbon nanotube. h Amine group grafted carbon nanotube.