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In fuel cell and electrolysis systems, hydrogen crossover is a phenomenon where hydrogen molecules (H2) permeate through a membrane, lowering the overall process efficiency and generating a potential safety risk. Many works have been reported to mitigate this undesired phenomenon, but it is yet difficult to accurately measure the rate of hydrogen crossover, particularly when the membrane is fully wetted in water. In this work, we investigated the pressure decay method as a simple, convenient, and low-cost method to characterize hydrogen crossover through wetted membranes for water electrolysis systems. Three different ion exchange membranes were analyzed: Nafion 212, Nafion 115, and in-house sulfonated poly(arylene ether sulfone). We rigorously confirmed our method and data by comparing it to the ANSI dataset with the current state-of-the-art equations of state (EOS) to account for the nonideality of high pressure hydrogen systems. The error from the gas non-ideality was less than 0.03%. As expected, the rate of hydrogen crossover showed high dependency on the temperature; more importantly, hydrogen crossover increased significantly when the membrane was fully soaked in water. For dry membranes, the proposed pressure decay method corroborated well with the literature data measured using other known methods. Moreover, for wetted membranes, the obtained data showed high similarity compared to the GC method which is currently the most reliable method in the literature. We attempted to predict the hydrogen permeability of wetted membranes using the solution diffusion model. The model based on the given thermodynamic parameters overestimated the hydrogen permeability, which can be used to estimate the ion channel tortuosity.

We chemically modify a commercially available elastomeric triblock copolymer, poly(styrene-b-ethylene-co-butylene-b-styrene) SEBS, to produce quaternary ammonium-functionalized hexyl bis(quaternary ammonium)-mediated partially-crosslinked SEBSs with different grafting degree of the conducting head groups as highly conductive and stable anion exchange membranes (AEMs). In an attempt to achieve a high ion exchange capacity and hence conductivity of the corresponding membranes without causing ‘gelation’, which these types of SEBS polymers typically experience, we use a SEBS with a high content (57%) of styrene, and graft the quaternary ammonium (QA) as both a crosslinker and the conducting head group on the side chain of the SEBS. The partial crosslinking approach, in combination with introducing these QA-conducting head groups as the side chain of the SEBS, helps to form larger ion clusters, and also to form a nano-phase morphology with long-range connecting channels. This induced the highest ion conductivity, 174.8 mS cm−1 at 80 °C, reported to date among these types of SEBS series. In addition, we obtain excellent cell performance with a current density of 450 mA cm−2 at 0.6 V and a peak power density of 315 mW cm−2 at 95% RH and 60 °C using the corresponding AEM.

Water channel formation of non-perfluorinated proton exchange membranes (PEMs) under a low humidifying condition is a very important issue, due to weaker phase separation between hydrophilic and hydrophobic moieties than in the case of perfluorinated PEMs such as Nafion. In this study, we performed Molecular dynamics (MD) simulations of hydrated sulfonated polyimide (SPI) models, one of the representative non-perfluorinated PEMs, under different temperature and humidifying conditions by removing water molecules continuously, reflecting experimental conditions of actual low humidifying fuel cell. The water channel morphology of sulfonated polyimide (SPI) models had no apparent temperature dependence. The hydrated SPI models show weak water channel formation even in a fully hydrated condition (λ = 16.4), consistent with our previous study, and they do not display significant temperature dependence on the water molecule distribution. As the λ value decreases from 16.4 to 2 (i.e., low humidifying conditions), the water molecules in the hydrated SPI models are evenly reduced. In particular, when the λ value of the hydrated SPI model decreases from 8.5 to 6, the size of the water clusters is significantly narrowed and the clusters become segregated, and this is also confirmed by an X-ray scattering analysis. As a result, the proton conducting performance of hydrated SPI models shows similar behavior with the change in water channel morphologies, which will be very important to design a novel non-perfluorinated hydrocarbon PEM with high performance for practical fuel cell systems.

In this study, poly(bisphenol-A-ether ketone) (PBAEK) is synthesized via nucleophilic aromatic substitution poly condensation between bisphenol A and 4,4-difluorobenzophenone, and the synthesized polymers are sulfonated using chlorosulfuric acid and suitable synthesis conditions for the temperature and sulfonating reagent content. The sulfonation degree of polymer is calculated using element analyses. The prepared sulfonated polymers are characterized for potential fuel cell applications through determining their water uptake, proton conductivity, and thermal stability. The significant advantage of the synthesized sulfonated PBAEK (sPBAEK) is its better solubility relative to commercial PEEK in various solvents, because sPBAEK backbones contain bisphenol A. The water uptake of the membrane increases with increases in the sulfonation degree. The sPBAEK membrane exhibits increased proton conductivity compared with the PBAEK membrane at 100% relative humidity conditions. As the sulfonation degree increases, the proton conductivity increases due to the increasing content in the hydrophilic domain. This property allows the prepared membranes to be potential candidates for proton exchange membrane fuel cells.

Anion exchange membrane fuel cells (AEMFCs) are regarded as potential alternatives to proton exchange membrane fuel cells (PEMFCs) for their system durability, low price and system similarity. However, their low ion conducting performance and membrane chemical stability needs to be overcome before practical applications of AEMFCs can be realized. In this study, we performed a molecular dynamics (MD) simulation of an ethyl imidazolium-functionalized poly(arylene ether sulfone) (EI-PES) block copolymer, which has high hydroxide ion conductivity due to a well-defined phase separation morphology, and compared the result with that of quaternary ammonium-functionalized PES (QA-PES). Introduction of ethyl imidazolium functional groups improved the ion conducting channel morphologies and chemical stabilities of the functional groups in AEMs compared to QA-PES models with the same polymer backbone but different functional groups, quaternary ammonium groups. Our findings are well consistent with the previous report that conjugated π-bonds of heterocyclic systems enhanced proton conductivity and chemical stability. In addition, compared to bulky functional groups, such as quaternary phosphonium and tertiary sulfonium, small size functional groups, such as ethyl imidazolium and quaternary ammonium, have a lower ion conducting performance under the same hydration conditions.

For membrane electrode assemblies (MEAs) consisting of hydrocarbon proton exchange membranes (PEMs) and Nafion-coated catalysts, the interfacial incompatibility between the membrane and electrodes has been a constant issue because it can seriously deteriorate the performance and long term stability of the MEAs. In this study, new bonding materials based on sulfonated aromatic copolymers with flexible and partially fluorinated structures (SPE/F) were prepared and tested as a proton conductive bonding layer on the surface of the hydrocarbon PEMs to increase the adhesive force to the catalyst layer. The SPE/F copolymers were synthesized by polycondensation of sulfonated and non-sulfonated dihalide monomers with two dihydroxy monomers, 4,4′-dihydroxy diphenyl ether (DHDPE) and hexafluoro bisphenol A (HFB). The molar feed ratio of DHDPE to HFB was varied (10:0, 7:3, and 4:6) in order to evaluate the effect of the polymer structure on the physical, electrochemical, and adhesive properties. With an increase in the HFB ratio, the proton conductivity and dimensional change of the resulting polymers decreased due to the enhanced chain rigidity and lower ion exchange capacity. The maximum adhesive strength of the bonding layer was obtained using a DHDPE:HFB ratio of 7:3 (SPE/F-7/3). Finally, the MEA utilizing SPE/F-7/3 as the bonding layer exhibited higher performance in the initial unit cell test, as well as a reduced increase in resistance after the durability cycling test compared with pristine MEA without the bonding layer.

In this study, we synthesized a novel poly(ether-ether-ketone), containing di(quaternary ammonium) hydroxide groups in the polymer chain. Then we tested the alkaline–exchange properties of a membrane made from the novel polymer, for fuel-cell applications. First, we synthesized a di-hydroxide monomer with amine groups, which were then converted to ammonium functional groups by immersion in hydroxide solution. Then, we synthesized poly(ether-ether-ketone) using a synthesized monomer and bisphenol A. We controlled the mole ratio of the quaternary ammonium hydroxide groups in the polymer structure to evaluate the performance of the membrane. The performances of polymer-electrolyte membranes with differing degrees of amination were compared. The optimum composition of the membrane was determined based on the chemical and thermogravimetric analyses, mechanical properties, the behavior of water in the membrane, and the level of ion conductivity.

Emulsion polymerization and post sulfonation methods are used to prepare polystyrene nanoparticles with a uniform size and particle size distribution, and sulfonated poly(etheretherketone) (sPEEK) for the fabrication of composite membranes. The polystyrene particles are functionalized with sulfonation reagents in order to enhance the proton conductivity. This study compares the performance of polymer electrolyte membrane fuel cells with different amounts of sulfonated nanoparticles and sulfonation reaction time of the PEEK polymer. The optimum composition of PS-SO3H particles is determined based on the mechanical properties, the behavior of water in the membrane, and the level of proton conductivity. The composite membrane has higher levels of proton conductivity than the pure sPEEK membrane. An increase in the content of PS particles increases the proton conductivity due to the incorporation of hydrophilic nanoparticles. These properties enable the composite membranes to become candidates for proton exchange membrane fuel cell applications.

In this paper, proton exchange membranes for direct methanol fuel cells were prepared by blending sulfonated poly(arylene ether sulfone) with poly (vinylidene fluoride-co-hecafluoropropylene)(PVdF-HFP) and polyethersulfone (PES) to decrease methanol permeability while maintaining high proton conductivity. The content of the second polymer, such as PES and PVdF, in the blend membranes was controlled at 10–40 wt% based on SPAES. In order to investigate the effects of the second polymer content in the blended membranes, parameters of the prepared membranes related to fuel cell performance were characterized, including their morphology, mechanical properties, methanol permeability, and proton conductivity. Surface roughness of the blend membrane was increased by the introduction of a hydrophobic polymer. Mechanical properties of the PES/SPAES blend membrane were improved owing to interaction between the sulfonic acid groups in SPAES and PES. However, the tensile strength of the PVdF/SPAES blend membrane was decreased by due to the poor compatibility of SPAES and PVdF. The methanol permeability in the blended membranes decreased with increasing content of PES and PVdF. The SPAES/PES blend membranes exhibited good proton conductivity and lower methanol permeability than the SPAES membrane. The SVdF15 blend membrane showed the highest selectivity due to the absence of methanol crossover and a small decrease of proton conductivity. These blend membranes are suitable for DMFC applications.

Crosslinked poly(arylene ether sulfone)s with pendant imidazolium units, both as crosslinkage sites and hydroxide conductors, were developed as anion exchange membranes (AEMs). These crosslinked membranes, with IECs of 0.80e1.21 meq/g, showed high hydroxide conductivity over 0.01 S/cm at 20