Phosphotungstic acid (HPW) molecules anchored in the bulk of Nafion as methanol-blocking membrane for direct methanol fuel cells

Approaches to the Modification of Perfluorosulfonic Acid Membranes

Polymer ion-exchange membranes are featured in a variety of modern technologies including separation, concentration and purification of gases and liquids, chemical and electrochemical synthesis, and hydrogen power generation. In addition to transport properties, the strength, elasticity, and chemical stability of such materials are important characteristics for practical applications. Perfluorosulfonic acid (PFSA) membranes are characterized by an optimal combination of these properties. Today, one of the most well-known practical applications of PFSA membranes is the development of fuel cells. Some disadvantages of PFSA membranes, such as low conductivity at low humidity and high temperature limit their application. The approaches to optimization of properties are modification of commercial PFSA membranes and polymers by incorporation of different additive or pretreatment. This review summarizes the approaches to their modification, which will allow the creation of materials with a different set of functional properties, differing in ion transport (first of all proton conductivity) and selectivity, based on commercially available samples. These approaches include the use of different treatment techniques as well as the creation of hybrid materials containing dopant nanoparticles. Modification of the intrapore space of the membrane was shown to be a way of targeting the key functional properties of the membranes.

Performance enhancement of direct methanol fuel cells using a methanol barrier boron nitride–Nafion hybrid membrane

Sulfonated hexagonal boron nitride is explored as a potential filler to prepare Nafion hybrid membranes for direct methanol fuel cell (DMFC) applications.

Elucidating the morphological aspects and proton dynamics in a hybrid perfluorosulfonic acid membrane for medium-temperature fuel cell applications

A perfluorosulfonic acid (PFSA) membrane, i.e. Nafion® 117, was doped with the heteropoly salts (HPS) Cs3PW12O40, Rb3PW12O40, and (NH4)3PW12O40. Also, composite membranes with CsxH3-xPW12O40 (x = 1, 2, and 3) as dopants were investigated, which were rendered insoluble by substituting protons with larger cations. Morphological assessment and a detailed analysis of the hopping events via SAXS measurement and analysis of the hydrogen bond networks were performed using classical and quantum hopping molecular dynamics simulation. The phase segregation decreased by increasing the extent proton substitution in HPA. HPS containing cations with a larger ionic radius induced smaller phase segregation in the membrane, as confirmed by the RDF plots. SAXS simulation revealed that the hydrophilic phase domains in the HPS-doped Nafion® membrane were spaced further apart than that in the HPA-doped membrane. Although there was a greater number of isolated clusters for the Cs3PW12O40-doped Nafion®, the average number of cluster decreased with an increase in the substitution cation/proton ratio and ionic radius of the cation. The analysis of the H-bond network stability revealed that the proton hops slower when the membrane contains HPS particles and the mean residence time of a proton on water molecules increases with an increase in the extent of proton substitution in H3PW12O40. Indeed, for the HPA-doped membrane, the diffusion of water molecules is lower than that in the HPS-doped system.

Formation and investigation of dual cross-linked high temperature proton exchange membranes based on vinylimidazolium-functionalized poly(2,6-dimethyl-1,4-phenylene oxide) and polystyrene

Dual-crosslinking provides a new strategy to enhance the dimensional and mechanical stabilities of membranes with high acid doping content and conductivity.

Aluminum-substituted phosphotungstic acid/sulfonated poly ether ether ketone nanocomposite membrane with reduced leaching and improved proton conductivity

Aluminum-substituted tungstophosphoric acid (AlTPA)/sulfonated poly ether ether ketone (SPEEK) (sulfonation degree approximately 77%) nanocomposite membranes have been prepared for fuel cell application. AlTPA nanoparticles are synthesized by the reaction of TPA and aluminum nitrate in aqueous medium. X-ray diffraction, energy dispersive X-ray, Fourier transform infrared and Raman spectroscopies, and field-emission scanning electron microscopy (FESEM) are used to characterize the AlTPA particles and SPEEK. Study reveals that 2.31 numbers of protons of TPA have been replaced by Al3+ in AlTPA with retention of Keggin’s structure. Nanocomposite membranes with varying AlTPA and TPA content are prepared and evaluated by measuring water uptake, ion exchange capacity, equilibrium water content, water desorption rate, proton conductivity, leaching tendency, and thermal properties. SPEEK/AlTPA nanocomposite membrane exhibits proton conductivity as high as 1.09 mS cm−1 at 10 wt% filler loading. Leaching of filler is reduced by approximately 92% in SPEEK/AlTPA nanocomposite membrane compared to SPEEK/TPA membrane. SPEEK/AlTPA membrane shows approximately 15% higher equilibrium water content and approximately 57% reduction in water desorption rate as compared to SPEEK/TPA membrane. Membranes are thermally stable up to 215°C, which is well above the operating temperature of fuel cells. Composite films are also examined by FESEM to gain further insights into the microstructure.

Nafion®/SiO2/m-BOT composite membranes for improved direct methanol fuel cell performance

Bentonite (BOT) has excellent hygroscopicity and large specific surface, so it is chosen as a dopant of Nafion® membranes in this paper.