Properties Of Proton Exchange Membranes Research Articles

The effect of polydopamine coated multi‐walled carbon nanotube on the wettability of sulfonated poly(ether ether ketone) nanocomposite as a proton exchange membrane

AbstractIn the present study, the effect of polydopamine coated multi‐walled carbon nanotube (PCNT) on the surface properties ‐wettability and surface free energy (SFE)‐ of a proton exchange membrane (PEM) nanocomposite based on sulfonated poly(ether ether ketone) (SPEEK) was studied. First, the polydopamine (PDA) coating process was optimized based on a response surface methodology (RSM), then PCNTs and the prepared PEM nanocomposites were characterized using field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), UV–vis spectroscopy, X‐Ray diffraction (XRD), differential scanning calorimetry (DSC), and atomic force microscopy (AFM) analyses. The physicochemical properties of membranes were also studied. The surface properties of PEMs were evaluated through estimating the SFE based on Owens, Wendt, Rabel, and Kaelble (OWRK) and Kwok and Neumann (K&N) theories; the SFE data revealed that OWRK is a more reliable method in this respect. Interestingly, the total SFE of SPEEK/PCNT nanocomposite did not notably change compared to the SPEEK membrane, but the polarity of SPEEK/PCNTs significantly decreased from 32.1% in SPEEK to 3.8% in the nanocomposite. This result could be attributed to the acid–base interaction of nanofiller and polymer, resulting in the involvement of polar group of polymer and new orientation of SPEEK chains at the surface of the nanocomposite.

Influence of crosslinking in phosphoric acid-doped poly(phenylene oxide) membranes on their proton exchange membrane properties

Phosphoric acid (PA)-doped membranes are promising electrolytes for high-temperature proton exchange membrane fuel cells (HT-PEMFCs). However, long-term durability issues have been an obstacle to their commercialization. Herein, we report a series of poly(phenylene oxide) (PPO)-based crosslinked membranes containing quaternary ammonium (QA) groups and exhibiting enhanced physicochemical stability and PA retention via ion-pair interactions between QA and PA. The degree of crosslinking in PPO by diamine crosslinker was controlled at 20, 30, and 40. The membranes were also crosslinked (degree = 20) using diamine crosslinkers with variable alkyl chain length (ethyl, butyl, and hexyl). All membranes exhibited sufficient thermal stability (5% weight loss temperatures (TD5%) = ∼230 °C) and oxidative stability (∼85% in the Fenton test). The PA uptake of the resulting membranes was controlled between 110 and 154% depending on their crosslinked structures. The membrane with the lowest degree of crosslinking (20) and shortest crosslinker exhibited the highest PA uptake and highest anhydrous proton conductivity (0.043 S/cm at 150 °C) in doped state. The proton conductivity was found to be significantly influenced by the PA uptake and crosslinked membrane structures. The highest PA retention of 89% was exhibited by the PA-doped membrane with the highest degree of crosslinking (40).

Trifluoromethyl functionalized sulfonated polytriazoles from diphenylphosphine oxide-based dialkyne via click polymerization: Effect of high content of phosphorus on the proton exchange membrane properties

A new diphenylphosphine oxide based dialkyne, [2,5-bis(prop-2-yn-1-yloxy)phenyl]diphenylphosphine oxide (POALK) has been prepared under mild reaction conditions. Using this POALK monomer, a new-fangled fluorinated sulfonated polytriazoles (PTPPS-70 to -90 and PTPS-100) with a high content of phosphine oxide moieties were prepared via the click polymerizations with other two comonomers [sulfonated diazide (DSAZ) and non-sulfonated phosphorus containing diazide (PFAZ)]. FT-IR and NMR (1H, 13C, and 31P) spectroscopic techniques were used for the structural elucidations of the synthesized monomer and polymers. The high molecular weight (weight average molecular weight: 59,600–75,800 g mol−1 and PDI: 1.65–2.20) sulfonated polymers demonstrated exceptional thermal, mechanical and thermomechanical steadiness. The higher content of phosphorus (3.83–4.54%) in the copolymers (IECW: 1.58–2.16 meq g−1) has occasioned excellent harmony among the water uptakes (WU), swelling ratios (SR), and proton conductivity (σ). The coexistence of triarylphosphine oxide units (both in the dialkyne and diazide monomers) in the polymers slowed down the peroxide radical attacks. The observed interconnected ionic nanochannels in the phase segregated morphology in AFM and TEM images of sulfonated polytriazoles (PTPPS-70 to -90 and PTPS-100) facilitate the proton transportation that resulted in high proton conductivity.

Surface initiated RAFT polymerization to synthesize N-heterocyclic block copolymer grafted silica nanofillers for improving PEM properties

Surface functionalization of silica nanoparticles (SiNP) has gained attention as an efficient methodology in improving the properties of the proton exchange membrane (PEM). Here, we report the development of block copolymer grafted SiNP (BC-g-SiNP) as functional nanofiller which was further blended with oxypolybenzimidazole (OPBI) to prepare nanocomposite-based PEM. Block copolymer chains consisting of poly (N-Vinyl imidazole) (pNVI) and poly (N-Vinyl-1,2,4-triazole) (pNVT) were grown on the SiNP surface using grafting-from RAFT polymerization in one pot process. Two series of BC-g-SiNP namely pNVI-b-pNVT-g-SiNP and pNVT-b-pNVI-g-SiNP were synthesized by altering the polymer chain grafting sequence. A series of BC-g-SiNP was developed by varying chain length of each block to understand the effect of the chain sequence and length on the properties of nanofiller and their influence in altering the PEM properties. The block copolymer structure, chain sequence and chain length were confirmed by means of NMR and GPC analysis of the cleaved copolymer chains. The BC-g-SiNP exhibited core-shell morphology and thickness of the shell altered as the chain length and sequence of the grafted chains tuned. Phosphoric acid (PA) loaded OPBI/BC-g-SiNP nanocomposite PEM showed very high thermal, mechanical and chemical stabilities along with the proton conductivity as high as 0.278 S cm-1 at 180 °C in case of OPBI/P6(3%). A very clear-cut dependence of the PEM properties was observed on the architecture of the BC-g-SiNP such as chain length and sequence.

Compressive Creep of Perfluorosulfonic Acid Membranes in Controlled Environments

For proton-exchange membrane (PEM) water-splitting electrolyzers (PEMWEs) to be commercially viable, PEMs must perform over long operational times in liquid environments under compression and therefore must exhibit good mechanical stability when hydrated [1], [2]. While a hydrated environment is an intrinsic result of the operation and membrane’s conductive function, it undermines PEM stability [3]. They are under unique mechanical stresses due to differential pressure affecting the active area, and high sealing pressures to prevent off-board leaks, thus, high differential pressure in PEMWEs makes compressive creep a great concern [4]. However, mechanical stability of PEMs is commonly characterized by tensile testing [5], the applicability of which to electrolyzers or technologies with similar cell designs is unclear. In this study, a compression setup was developed to monitor creep response of hydrated PEMs in situ and in controlled temperature.Water-splitting electrolyzers are a key technology for enabling the hydrogen economy and reshaping the renewable energy landscape. Among the most viable candidates for the low-temperature electrolyzers is the proton-exchange membrane (PEM) water-splitting electrolyzers (PEMWEs), which uses an ion-conductive polymer solid-electrolyte. Stability, in liquid environments at temperatures ranging from 50 to 80 °C, is an important aspect of PEM design considerations. While hydration, pressure, and temperature are used as design parameters for optimizing electrolyzer performance, their role in durability is not established [5]. This creates a gap between performance and lifetime assessment of membranes for electrolyzers. Thus, there is need for a metric that could capture membrane durability by accounting for performance operators. This study identifies compression creep as a potential material stability metric that can account for the operation-dependent variables, such as pressure, dehydration, and temperature, and provides guidance for better assessment of membrane lifetime in electrolyzers and similar electrochemical devices.Our results show compressive response of perfluorosulfonic acid (PFSA) membranes is significantly different than tensile behavior in both dry and hydrated states [6]. Moreover, PEMs exhibit creep response under compression with continuous decrease in its thickness over 24 hours, with a dependence on the applied pressure and temperature [6]. This work demonstrates the importance of studying the mechanical properties of PEMs under compression, which is more relevant to the stress-states the membrane undergoes during operation in an electrolyzer and similar electrochemical devices.

Influence of PtCu/C Catalysts Composition on Electrochemical Characteristics of Polymer Electrolyte Fuel Cell and Properties of Proton Exchange Membrane

The present work aimed to investigate the influence of “weakly bound“ copper dissolution from the surface of bimetallic PtCux/C catalysts on the properties of proton exchange membrane and the membrane electrode assembly (MEA) in general. A number of PtCux/C materials have been obtained by the simultaneous reduction in copper and platinum precursors in the course of liquid-phase synthesis with a varying ratio of metals from PtCu2.0/C to PtCu0.3/C. All bimetallic PtCux/C electrocatalysts after the activation stage exhibit high activity in the oxygen electroreduction reaction. The PtCux/C catalysts in “as prepared” state were tested in MEA. The increase in Cu content in PtCux/C catalysts led to a decrease in current density of MEA while its resistance was almost independent of the Cu fraction in the catalyst. The membrane saturation degree by Cu2+-ions after MEA testing did not exceed 40%, even in the case of the PtCu2.0/C material. The main reason for the degradation of membrane electrode assembly with PtCux/C materials is the transport limitation caused by the contamination of Nafion in three catalytic layer by “weakly bound” copper ions.

Bioinspired layered proton-exchange membranes with high strength and proton conductivity

High-performance proton exchange membranes (PEMs) are crucial to the overall performance of PEM fuel cells. However, there always exists a conflict between the high ion conductivity and mechanical properties of traditional PEMs. Herein, we have demonstrated a simple bioinspired strategy for fabricating nacre-inspired layered membrane (GPS-X) based on GO sheets by crosslinking two kinds of long-chain polymers (PDA and SPVA) via vacuum filtration. Strikingly, the resulting GPS-50 membrane is endowed with high tensile strength (216.5 MPa) and high proton conductivity (0.303 S cm−1 at 80 °C) due to the combination of strong interfacial interactions and well-developed 2D channels, which surpasses Nafion and many other reported GO-based PEMs. Furthermore, the membrane exhibits higher output-power but lower weight than Nafion 212. Considering the achieved excellent properties induced by the independently adjustable 2D channels and mechanical properties, the bioinspired strategy offers guidance for constructing advanced membrane materials with potential applications in fuel cells.

Effect of sulfonic acid‐functionalized polysilsesquioxane on new semifluorinated sulfonated polytriazole composites and investigation of proton exchange membrane properties

AbstractA new semifluorinated sulfonated copolytriazole is synthesized, maintaining a particular degree of sulfonation of 80% following the click reaction of two terminal azides 1,4‐bis‐[{2′‐trifluromethyl 4′‐(4″‐azidophenyl)phenoxy}]phenyl, and 4,4′‐diazido‐2,2′‐stilbenedisulfonic acid disodium salt with equal molar amounts of two dialkyne monomers namely, 1,3‐diethynylbenzene and 3,5‐bis(prop‐2‐ynyloxy)benzoic acid and designated as PTEHCSH‐80. Further, the copolytriazole is used to prepare polymer composites employing the sol‐gel reaction of the starting precursor sol 3‐(trihydroxylsilyl) propane‐1‐sulfonic acid. The weight percentage (wt%) of the filler is varied from 0 to 10 wt%, and a series of polymer composite films are prepared and abbreviated as PTEHCSH‐80/X (where X is wt% of the filler, X = 0. 2.5, 5.0, 7.5, 10.0). All the polymer composites are characterized through FTIR spectroscopic techniques. The composite films revealed various desirable properties such as high thermochemical and dimensional and mechanical stabilities in their corresponding acid form. Moreover, the composites exhibited proton conductivities ranging from 62 to 98, 117 to 182, and 131 to 195 mS/cm at three different temperatures 30°C, 80°C, and 90°C, respectively, in a hydrated state.

Sulphonated polysilsesquioxane–polyimide composite membranes: proton exchange membrane properties

This study reports the preparation of a –COOH-containing sulphonated copolymer (SPI-COOH-70) and its composite membranes. The composite membranes (SPI/SS-X) were prepared by using the solution casting route by adding different weight percentages of 3-(trihydroxysilyl) propane-1-sulphonic acid into SPI-COOH-70 solution. The proton exchange membrane properties such as morphology, ion-exchange capacity, water uptake and proton conductivity of the prepared composite membranes were studied as a function of sulphopropylated polysilsesquioxane (SiOPS) filler and temperature. All the SPI/SS-X composite membranes showed high-thermal stability and chemical stability, which are attributed to the presence of polar phosphine oxide and the wholly aromatic nature of the copolymers. The homogeneous distribution of the SiOPS nanoparticles in the polymer matrix observed from the scanning electron microscopy and atomic force microscopy images are attributed to the formation of covalent bonds between the –OH and –COOH groups of SiOPS and SPI-COOH-70, respectively. The composite membranes with 10 wt% SiOPS exhibited much higher proton conductivity (205 mS cm−1), which is much higher than that of the pristine copolymer membrane (114 mS cm−1) under similar experimental conditions. The improvement in proton conductivity is attributed to the presence of pendant sulphonic acid groups in the nanofiller, which provides a better proton transport pathway in the composite membranes.

Carbon corrosion behaviors and the mechanical properties of proton exchange membrane fuel cell cathode catalyst layer

Carbon corrosion-induced catalyst layer destruction is the primary reason to the performance decay of proton exchange membrane fuel cells (PEMFCs). In this study, the accelerated stress test (AST) on carbon corrosion was conducted, and real-time CO2 evolution was measured in-situ by non-dispersive infrared (NDIR) analysis. The performance degradation was investigated by the reduction of the current density and the loss of electrochemical active surface area (ECSA) of Pt. The loss of catalyst layer porosity and increase of mass transport resistance were investigated by the visible reduction of porosity and thickness in the cathode catalyst layer (CCL). Further mechanical tensile tests showed that the elastic modulus of CCL remained unchanged initially, and then increased probably due to the compaction of CCL. In the final step, it decreased due to the complete failure of the material. Thus, carbon corrosion was proved to alter the mechanical strength of CCL.

Ceria Stabilized by Titanium Carbide as a Sustainable Filler in the Nafion Matrix Improves the Mechanical Integrity, Electrochemical Durability, and Hydrogen Impermeability of Proton-Exchange Membrane Fuel Cells: Effects of the Filler Content.

Cerium oxide-anchored titanium carbide (CeO2-TiC) is realized as a potential inorganic filler when modifying the Nafion matrix of a proton-exchange membrane fuel cell (PEMFC). A hydrothermal strategy was employed to synthesize CeO2-TiC of high crystallinity as a filler to mitigate the problematic properties of a proton-exchange membrane (PEM). CeO2-TiC with a weight ratio of 0.5, 1, 1.5, or 2% was incorporated into a Nafion matrix to form a hybrid by adopting a solution-casting procedure. Reinforcement owing to the presence of TiC provides increased tensile strength to PEM, and the addition of CeO2 improves the durability of PEM by scavenging free radicals. The microstructural, thermomechanical, physiochemical, and electrochemical properties of PEM, including contact angle, water sorption, water uptake, and proton conductivity, were extensively studied. Random dispersion of CeO2-TiC in the Nafion matrix improves the thermal stability, tensile strength, and water uptake while retaining proton conductivity, as compared with those of pristine Nafion. As a result, optimized Nafion/CeO2-TiC (1 wt %) achieved undiminished PEMFC performance compared to that of pristine Nafion while operating the device at 60 °C and 100% relative humidity. In addition, Nafion/CeO2-TiC (1 wt %) experienced the degradation of merely 0.6 mV h-1 during 200 h operation under identical conditions. Compared to that of Nafion/CeO2-TiC (1 wt %), pristine Nafion and Nafion-212 displayed accelerated and comparable degradation (for pristine Nafion, 1.3 mV h-1; for Nafion-212, 0.4 mV h-1). PEMFC power output, hydrogen permeability, and morphology of samples were examined after the durability test; the results indicate that Nafion/CeO2-TiC (1 wt %) is extremely stable. Since various Nafion hybrids have been reported as highly durable PEMs, this study is expected to open up new perspectives to expanding their applications, especially in sustainable PEMFC technology.

Synthesis and characterization of star-shaped sulfonated new poly(ether triazole)s: Proton exchange membrane properties

Several star-shaped sulfonated poly(ether triazole)s abbreviated as PTAPSH-XX was prepared by Cu (I) catalyzed click polymerization of a mixture of a new tri-azide monomer namely, 4,4-tris[3-trifluoromethyl-4(4-azidophenoxy)phenyl]biphenyl (PGZ) (B3) and 4,4′-diazido-2,2′-stilbene disulfonic acid disodium salt (DADSDB) with an equimolar amount 4,4′-(propane-2,2-diyl) bis((prop-2-ynyloxy)benzene) (BPEBPA). The degree of sulfonation of the prepared copolymers was varied by changing the molar ratio of DADSDB in the polymer feed. The monomer and copolymers were characterized by FTIR and NMR spectroscopic techniques. The salt form of the branched copolymers was converted into flexible membranes by solution casting technique using dimethyl sulfoxide (DMSO) as solvent and was converted to their acid form by acidification in 1.5 M H2SO4. The introduction of the branching unit largely governs the physicochemical properties and proton conductivity of the membranes. The polymers displayed desirable set of properties required proton exchange membrane applications like high thermal stability (Td10 ~ 259–290 °C), low water uptake and excellent dimensional integrity. The membranes also displayed improved mechanical properties (TS = 51 to 73 MPa, YM = 2.07 to 2.37 GPa), enhanced oxidative stability and high proton conductivity (44 to 102 mS cm−1 at 80 °C). The TEM images of the PTAPSH-XX membranes revealed excellent phase segregated morphology with the formation of ionic clusters within 15 to 90 nm.

Synthesis and characterization of new sulfonated copolytriazoles and their proton exchange membrane properties

ABSTRACTThis work reports the synthesis and characterization of a series of new sulfonated copolytriazoles. The polymers were prepared by CuI catalyzed 1,3‐cycloaddition reaction of an equimolar amount of a dialkyne monomer, 1,3‐diethynylbenzene and a mixture of two diazide monomers, namely, 4,4′‐diazidodiphenyl ether and 4,4′‐diazido‐2,2′‐stilbenedisulfonic acid disodium salt. The copolymers showed high inherent viscosity indicating the formation of high molar mass product. The copolymers were characterized by Fourier transform infrared and proton nuclear magnetic resonance spectroscopic techniques. The copolymer membranes displayed moderate water uptake, high dimensional, mechanical, and thermal stability. Transmission electron microscopy micrographs displayed excellent phase‐separated morphology along with very fine ionic clusters. The copolymer PTEOSH‐90 (90% degree of sulfonation) showed much higher proton conductivity value which is up to 196 mS cm−1 at 80 °C in completely hydrated condition compared to that of Nafion (165 mS cm−1). © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48514.

Effects of grafting parameters on the properties of proton exchange membranes based on sulfo-functionalized porous silicon for micro direct methanol fuel cells

Abstract 3-Mercaptopropyltrimethoxysilane [MPTMS, (CH3O)3SiCH2CH2CH2SH] can be grafted to porous silicon via a simple chemical grafting method and then sulfonated to prepare a proton exchange membrane (PEM) for application in micro direct methanol fuel cells (μDMFCs). The concentration of MPTMS and the pH of the solvent, which is varied by adding glacial acetic acid (GAA), play important roles in the chemical grafting process. In this work, PEMs based on sulfo-functionalized porous silicon were prepared at MPTMS concentrations ranging from 10 wt.% to 90 wt.% and GAA concentrations ranging from 0 wt.% to 10 wt.% to study the effects of grafting parameters on the proton transport properties of PEMs. Electrochemical impedance spectroscopy shows that the proton conductivity of the PEMs can be tuned by changing the MPTMS and GAA concentrations, and it reaches a maximum of 0.082 S/cm at an MPTMS concentration of 30 wt.% and a GAA concentration of 5 wt.%. The effects of MPTMS and GAA concentrations on the properties of PEMs are discussed in the context of two competitive reaction pathways of MPTMS molecules: dehydration condensation with silanols on the walls of porous silicon and self-polymerization.

Correlated interfacial water transport and proton conductivity in perfluorosulfonic acid membranes.

Water must be effectively transported and is also essential for maximizing proton conductivity within fuel-cell proton-exchange membranes (PEMs). Therefore, identifying relationships between PEM properties, water transport, and proton conductivity is essential for designing optimal PEMs. Here, we use coherent Raman spectroscopy to quantify real-time, in situ diffusivities of water subspecies, bulk-like and nonbulk-like (interfacial) water, in five different perfluorosulfonic acid (PFSA) PEMs. Although the PEMs were chemically diverse, water transport within them followed the same rule: Total water diffusivity could be represented by a linear combination of the bulk-like and interfacial water diffusivities. Moreover, the diffusivity of interfacial water was consistently larger than that of bulk-like water. These measurements of microscopic transport were combined with through-plane proton conductivity measurements to reveal the correlation between interfacial water transport and proton conductivity. Our results demonstrate the importance of maximizing the diffusivity and fractional contribution of interfacial water to maximize the proton conductivity in PFSA PEMs.

Mesoscale modeling of sulfonated polyimides copolymer membranes: Effect of sequence distributions

We adopt dissipative particle dynamics simulation technique and systematically study the effect of sequence distributions of hydrophobic and hydrophilic segments in individual sulfonated polyimide (SPI) copolymer on the micro-phase separated structure and the performance of proton exchange membranes (PEMs) under various water contents. The phase morphology as well as the shape and size of water channels is affected by sequence distributions. Compared to the di-block copolymer and the alt-copolymer, water channels in the multi-block copolymer are more homogenous. Additionally, the copolymer sequence distributions affect the water transport which is closely related to the proton conductivity, the dimensional stability and the mechanical properties of PEMs via tuning the phase structure. Generally, the more homogenous water channels the faster water transport. As for the dimensional stability, unlike the other two copolymers the unique shrinkage behavior of multi-block copolymer can resist the membrane swelling induced by water uptake. Moreover, the system with short block has relatively large Young's modulus and the influence of sequence distributions on Young's modulus weakens with the addition of water. Consequently, the multi-block SPI copolymer possesses fast water transport, low dimension-swelling and relatively high Young's modulus, which will make it a potentially huge application in PEM.

Novel Sulfonated Co-poly(ether imide)s Containing Trifluoromethyl, Fluorenyl and Hydroxyl Groups for Enhanced Proton Exchange Membrane Properties: Application in Microbial Fuel Cell.

A hydroxyl group containing new cardo diamine monomer was synthesized, namely 9,9-bis (hydroxy- (4'-amino(3-trifluoromethyl)biphenyl-4-oxy)-phenyl)-9H-fluorene (mixture of isomers, HAPHPF). HAPHPF, along with a sulfonated diamine monomer, 4,4'-diaminostilbene-2,2'-disulfonic acid (DSDSA), was used to prepare a series of new sulfonated copolyimides by polycondensation with 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA). The degree of sulfonation (DS < 1) was adjusted by the feed ratio of DSDSA/HAPHPF and the copolymers were named as DHN-XX, where XX denotes the mole percentage of DSDSA (XX = 50, 60, and 70). The copolymers showed high molecular weights. The copolymer structure and composition were confirmed by FTIR and NMR techniques. Copolymer membranes were prepared through solution cast route by using dimethyl sulfoxide as a solvent. The membranes showed high thermal, mechanical, hydrolytic and peroxide radical stability, and low water uptake and low swelling ratios. Well-separated hydrophilic and hydrophobic phase morphology was observed in TEM and AFM images of the copolymer membranes and was further supported by the SAXS studies. The proton conductivity of the DHN-70 was as high as 97 mS cm-1 at 80 °C and the value is significantly higher than that of the nonhydroxylated analogue. The membranes also showed superior microbial fuel cell (MFC) performance, similar like Nafion 117 under similar test conditions. The chemical oxygen demand removal values provide substantial evidence that the fabricated membranes can be utilized in bioelectrochemical systems.

Sulfonated copolyimides containing trifluoromethyl and phosphine oxide moieties: Synergistic effect towards proton exchange membrane properties

This paper reports the synthesis and characterization of a series of new semi-fluorinated sulfonated copolyimides (co-SPI) using a new trifluoromethyl and phosphine oxide containing diamine monomer, namely bis[4-(4′-aminophenoxy)-3-trifluoromethyl phenyl] phenylphosphine oxide (DFPPO). The copolymers were prepared by one pot polycondensation reaction of a mixture of two diamine monomers, namely 4,4′-diaminostilbene-2,2′-disulfonic acid (DSDSA) and DFPPO with the equimolar amount of 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA). All these copolymers were soluble in several organic solvents and size exclusion chromatography indicated the formation of high molar masses. The membranes prepared from these copolymers by solution casting route showed good mechanical properties. The polymers were characterized by FTIR and NMR spectroscopic techniques that confirmed the polymer repeat unit structures. The degree of sulfonation of the copolymers was determined from 1H NMR signal intensities. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) images of the membranes showed phase separated morphology. In general, all the copolyimides showed high proton conductivity and reasonably high oxidative and hydrolytic stability. The co-SPI membrane DFPNH-90 (90% degree of sulfonation) with IECW=2.86 mequiv g−1 showed proton conductivity as high as 237mScm−1 at 80°C.

Genetic Algorithm-based Modeling of PEM Fuel Cells Suitable for Integration in DC Microgrids

Operating conditions such as temperature and pressure affect the fuel cell performance. Proton Exchange Membrane (PEM) fuel cells work at its maximum efficiency when it is operated within temperature limits. To improve the heat transfer properties of PEM fuel cells, nano coolants are added. Identification of a suitable combination of thermal conductivity, relative humidity, and parametric coefficients for performance assessment of PEM fuel cells in real time is mandatory. Conventional methods follow complex computations and trial and error procedure to model fuel cell without thermal management parameters. Hence, in this paper, the objective of parameter set identification is framed as an optimization problem and solved using Genetic Algorithm method. The performance of the proposed approach is evaluated for different test conditions and validated through simulation findings.

Transport in Proton Exchange Membranes for Fuel Cell Applications-A Systematic Non-Equilibrium Approach.

We hypothesize that the properties of proton-exchange membranes for fuel cell applications cannot be described unambiguously unless interface effects are taken into account. In order to prove this, we first develop a thermodynamically consistent description of the transport properties in the membranes, both for a homogeneous membrane and for a homogeneous membrane with two surface layers in contact with the electrodes or holder material. For each subsystem, homogeneous membrane, and the two surface layers, we limit ourselves to four parameters as the system as a whole is considered to be isothermal. We subsequently analyze the experimental results on some standard membranes that have appeared in the literature and analyze these using the two different descriptions. This analysis yields relatively well-defined values for the homogeneous membrane parameters and estimates for those of the surface layers and hence supports our hypothesis. As demonstrated, the method used here allows for a critical evaluation of the literature values. Moreover, it allows optimization of stacked transport systems such as proton-exchange membrane fuel cell units where interfacial layers, such as that between the catalyst and membrane, are taken into account systematically.