Increases in the proton conductivity and selectivity of proton exchange membranes for direct methanol fuel cells by formation of nanocomposites having proton conducting channels

Abstract

We explore an approach to effectively enhance the properties of cost-effective hydrocarbon protonexchange membranes for application in the direct methanol fuel cell (DMFC). This approach utilizes sulfonated silica nanoparticles (SA-SNP) as additives to modify sulfonated poly(arylene ether ether ketone ketone) (SPAEEKK). The interaction between the sulfonic acid groups of SA-SNP and those of SPAEEKK combined with hydrophilic-hydrophobic phase separation induce the formation of proton conducting channels, as evidenced by TEM images, which contribute to increases in the proton conductivity of the SPAEEKK/SA-SNP nanocomposite membrane. The presence of SA-SNP nanoparticles also reduces methanol crossover in the membrane. Therefore, the SPAEEKK/SA-SNP nanocomposite membrane shows a high selectivity, which is 2.79-fold the selectivity of Nafion ® 117. The improved selectivity of the SPAEEKK/SNP nanocomposite membrane demonstrates potential of this approach in providing hydrocarbon-based PEMs as alternatives to Nafion in direct methanol fuel cells.

Preparation, characterization and properties of PVDF-g-PAMPS/PMMA- co -PAMPS/silica nanoparticle as a new proton exchange nanocomposite membrane

“…However, the nanocomposite membrane containing 10% silica nanoparticles showed a decrease in water uptake value. The contradictory effects of silica nanoparticles on the water uptake behavior have also been reported in the literatures [26,30]. Two contradictory aspects for silica nanoparticles which effect on the water uptake behavior have been offered.…”

“…10B-E), the honey comb-like structure and high porosity of these membranes can provide free volumes to absorb water molecules and thereby increasing the water uptake. The absorbed water can be divided into two groups of bound water and free water [26][27][28]. The absorbed water by the membrane as a proton carrier and proton hopping sites play a key and complex role in the proton transport phenomena.…”

“…In the vehicle mechanism, the proton diffusion across membrane occurs in combination with solvent molecules as proton carriers. Hence, the presence of free volumes and interconnected pore structure is vital to absorb water and the proton transport across proton exchange membrane [26][27][28][29]. Rigidity of polymer backbone, absence of free volume and interconnected pore in the dense membranes confine the diffusion and transport of proton in the proton exchange membrane by the vehicle mechanism.…”

“…Two contradictory aspects for silica nanoparticles which effect on the water uptake behavior have been offered. All of the related works suggested that increasing water uptake is closely related to hygroscopic effect of silica nanoparticles by providing sites that can absorb water, those being both the silica nanoparticles and the sulfonic acid groups, which help to increase the content of bound water [26,30]. Another considerable aspect explains a cross-linking effect of silica nanoparticles and a probable interaction between silica nanoparticles and polymer [26,31].…”

“…All of the related works suggested that increasing water uptake is closely related to hygroscopic effect of silica nanoparticles by providing sites that can absorb water, those being both the silica nanoparticles and the sulfonic acid groups, which help to increase the content of bound water [26,30]. Another considerable aspect explains a cross-linking effect of silica nanoparticles and a probable interaction between silica nanoparticles and polymer [26,31]. Together, the crosslinking effect of silica nanoparticle results in reduction of polymer chain mobility (free volume) and the space where absorbed water can be located [26,31].…”