Abstract
A membrane electrolyte that restricts the methanol cross-over while retaining proton conductivity is essential for better electrochemical selectivity in direct methanol fuel cells (DMFCs). Extensive research carried out to explore numerous blends and composites for application as polymer electrolyte membranes (PEMs) revealed promising electrochemical selectivity in DMFCs of carbon nanomaterial-based polymer composites. The present review covers important literature on different carbon nanomaterial-based PEMs reported during the last decade. The review emphasises the proton conductivity and methanol permeability of nanocomposite membranes with carbon nanotubes, graphene oxide and fullerene as additives, assessing critically the impact of each type of filler on those properties.
Highlights
Direct methanol fuel cells (DMFCs) belong to a category of polymer electrolyte membrane fuel cells (PEMFCs) that utilize a liquid fuel to produce electrical power at room temperature
DMFCs do not require humidification accessories which significantly reduce the complexity, the volume and weight of the system compared to H2-fueled PEMFCs
A significant decrement in proton conductivity up to 50% is observed for 5 wt.% sulfonated polyether ether ketone (SPEEK)-SiO2-CNTs due to reduced sulfonic acid concentration, while the methanol permeability is lowered by one order of magnitude (3.42 × 10−7 to 4.22 × 10−8 cm2 s−1)
Summary
Direct methanol fuel cells (DMFCs) belong to a category of polymer electrolyte membrane fuel cells (PEMFCs) that utilize a liquid fuel to produce electrical power at room temperature. (◦C) Ref. AAmmoonngg tthhee ccaarrbboonn mmaatteerriiaallss,, ggrraapphheennee ooxxiiddee aanndd ccaarrbboonn nnaannoottuubbeess hhaavvee bbeeeenn ggiivveenn ggrreeaatteerr aatttteennttiioonn aaccccoorrddiinngg ttoo tthhee aannaallyyssiiss ooff bbiibblliioommeettrriicc ddaattaa ffrroomm llaasstt tteenn yyeeaarrss ddeeppiicctteedd iinn FFiigguurree 55. In spite of substantial reduction in methanol permeability (from 2.25 × 10−6 cm s−1 to 3.12 × 10−7 cm s−1), Nafion®-SiO2-CNTs composite membrane shows lower proton conductivity due to the disturbance in supramolecular self-assembly of Nafion® [91]. To eliminate this problem, SiO2-CNTs further immobilized with phosphotungstic acid (PWA) can actively participate in proton transport by interacting with hydrophilic sulfonic acid groups of Nafion®. The conductivity of Nafion®-PWA-SiO2 composite is maintained on par with pristine Nafion®, while the methanol permeability is further reduced (to 2.63 × 10−7 cm s−1)
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