Nanoscale morphology in sulphonated poly(Ether ether ketone)-based ionomeric membranes: Mesoscale simulations

The model of a proton-conducting membrane based on sulfonated aromatic poly(ether ether ketone) has been constructed in the context of the mesoscale-dynamics method. The structure of the polymer is represented as a linear adjusted sequence of polar and nonpolar chain units. The degree of sulfonation and water content in the system are the main parameters during calculations. The constructed model shows that microphase separation of hydrophilic and hydrophobic polymer chain units occurs even at small water contents. A spatial network of water domains that has walls made of polymer-matrix polar chain units is formed within the membrane volume. The estimation of the percolation threshold demonstrates that water domains form a penetrating system of channels at water contents as low as 5–9%. Analogous simulations have been performed for the well-studied Nafion-1100 membrane. Although the morphologies of hydrophilic channels in sulfonated aromatic poly(ether ether ketone) and Nafion differ substantially, their cross sections are close. The results make it possible to consider sulfonated aromatic poly (ether ether ketone) a possible alternative to Nafion during the development of proton-conducting membranes for new-generation fuel cells.     

The mesoscopic modeling of the structure of a hydrated ionomeric membrane based on a sulfonated aromatic poly(ether-ether-ketone)

A proton conducting hydrated membrane on the basis of sulfonated aromatic poly(ether-ether-ketone) was modeled for the first time using dynamic density functional theory (the “mesoscopic dynamics” method). The model constructed was used to demonstrate the microphase separation of hydrophilic and hydrophobic polymer chain units in the selected region of parameters. A spatial network of water domains formed in the membrane volume. The domain walls consisted of polar (sulfonated) macromolecule units. A comparison with the well-studied Nafion-1100 membrane showed that the cross sections of water channels in the two systems had similar values. This must ensure approximately equal ionic conductivity characteristics.     

Structural and transport phenomena of urocanate-based proton carrier in sulfonated poly(ether ether ketone) membrane composite

Proton transport is one of crucial phenomena in electrolytic part highly considered to overcome a limit in fuel cell efficiency improvement. Proton conducting organic electrolyte was modeled and simulated at atomistic level of calculation by doping of butyl urocanate (C4U), a composite material with imidazole substructure, with sulfonated poly(ether ether ketone) (SPEEK) amorphous membrane at various working temperature. Molecular dynamics simulations were used to investigate structural and dynamics characteristic of C4U in the membrane comparing with the SPEEK-hydronium membrane model as a control. From simulations, thermal effect on water and proton carriers cluster surrounding the sulfonate groups was explored. At higher temperature, the more transport dynamics of C4U ions in SPEEK membranes were found than that of hydronium ions in the control system. Likewise, phase separation of hydrophobic and hydrophilic parts was taken into consideration here. A critical role of the enhancing proton conductivity by increasing the diffusion coefficient at temperature beyond C4U melting point in composite polymer membrane was emphasized. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1625–1635     

Sulfonated carbon nanotubes/sulfonated poly(ether sulfone ether ketone ketone) composites for polymer electrolyte membranes

A series of composite membranes consisting of sulfonated carbon nanotubes (sCNTs) and sulfonated poly(ether sulfone ether ketone ketone) were successfully fabricated via the solution casting method. The chemical structure, as well as the long‐term stability of the sCNTs in different solvents, was investigated by Fourier transform infrared (FTIR) analysis and solubility experiment, respectively. The morphology, tensile strength, proton conductivity, and methanol permeability of the composite membranes were also investigated. The scanning electron microscope (SEM) observation indicated the good dispersion of the carbon nanotubes in polymer matrix as well as the strong interfacial bonding between the sulfonated poly(ether sulfone ether ketone ketone) (SPESEKK) matrix and sCNTs. The addition of either pristine carbon nanotubes or modified carbon nanotubes significantly enhanced the tensile strength of the SPESEKK membrane. The proton conductivity of the SPESEKK membrane increased while the methanol permeability decreased as the sCNTs content increased, showing a strong interaction between the modified nanotubes and SPESEKK. Copyright © 2010 John Wiley & Sons, Ltd.     

Preparation and characterization of monovalent cation selective sulfonated poly(ether ether ketone) and poly(ether sulfone) composite membranes

Highly charged cation permeable composite membranes were prepared by blending of sulfonated poly(ether sulfone) (SPES) with sulfonated poly(ether ether ketone) (SPEEK) in 0 to 90% weight ratio, to adjust the hydrophobic properties and ion selective nature. Extent of sulfonation was confirmed by 1H NMR and ion exchange capacity and degree of sulfonation depending on blending composition. These membranes were characterized as a function of weight fraction of SPEEK by recording ion-exchange capacity, water uptake, thermogravimetric analysis, membrane conductivity and membrane potential in equilibration with different electrolytic solutions. Membrane permselectivity and solute flux were estimated using these data on the basis of non-equilibrium thermodynamic principles and for observing the selectivity of different membranes for mono- or bivalent counter-ions. It was observed that relative selectivity for monovalent in comparison to bivalent counter-ions were increased with the decrease in SPEEK content in the composite membrane matrix. The range of SPEEK content in the blend from 60 to 80% appears the most suitable for the selective separation of monovalent ions from bivalent ions. Furthermore, highly charged nature and stabilities of these membranes extend their applications for the electro-assisted separations of similarly charged ions as well as other electro-membrane processes.     

Sulfonated poly(fluorenyl ether) membranes containing perfluorocyclobutane groups for fuel cell applications

This paper describes the preparation and electrochemical properties of new proton conducting polymer membranes, sulfonated poly(fluorenyl ether) membrane-containing perfluorocyclobutane (PFCB) moieties for fuel cell applications. The sulfonated polymers were prepared via thermal cyclodimerization of 9,9-bis(4-trifluorovinyloxyphenyl)fluorene and subsequent post-sulfonation using chlorosulfonic acid (CSA) as a sulfonating agent. The post-sulfonation reaction was carried out by changing the molar ratio of CSA/repeating unit of the polymer at room temperature for 5 h and the resulting sulfonated polymers showed different degrees of sulfonation (DS) and ion exchange capacities (IEC). With the increment of CSA content, the DS, IEC and water uptake of the sulfonated polymer membranes increased. Their proton conductivity was investigated as a function of temperature. The polymer membrane with an IEC value of 1.86 mmol/g showed a water content of 25% similar to Nafion-115's but showed higher proton conductivity than Nafion-115 over the temperature 25–80 °C. The polymer membrane with lower water uptake and higher IEC showed similar proton conductivity and methanol permeability to Nafion-115. These results confirmed that the sulfonated poly(fluorenyl ether)-containing PFCB groups could be a promising material for fuel cell membranes.     

Ionic conducting membranes based on new sulfonated poly(arylene ether ketone)s for fuel cell applications

The synthesis and characterization of new di‐ and tetra‐sulfonated ether diketone monomers are described. From these monomers, a wide series of sulfonated poly(arylene ether ketone)s (SPAEK) are synthesized by varying the sulfonic acid repartition along the polymer backbones. Their chemical structures are thoroughly characterized by NMR. From these polymers tough membranes are obtained from solution casting method and their water uptake, ionic conductivity, and water/gas permeation properties are determined and compared with those of Nafion membrane. Preliminary fuel cell tests show that SPAEK membranes are promising candidates for fuel cell application. This work brings new insights concerning the beneficial effects of introducing densely sulfonated monomers in a polyarylether macromolecular structure along with fluorinated groups improving conductivity while reducing unwanted excessive swelling. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 771–777     

Sulfonated poly(ether ether ketone)/polyaniline composite proton-exchange membrane

Sulfonated poly(ether ether ketone) (PEEK) was prepared by sulfonation of commercial Victrex^@ PEEK and degree of sulfonation was found to be about 44.5% by ¹H NMR. Sulfonated PEEK/polyaniline composite membranes, in order to prevent methanol crossover, were prepared by chemical polymerization of a thin layer of polyaniline (PANI) in the presence of a high oxidant concentration on a single face modification. FTIR and PANI coating density studies confirmed the loading of PANI in sulfonated PEEK membrane matrix. PANI composite membranes with different polymerization time were prepared and subjected to thermogravimetric analysis as well as electrochemical and methanol permeability study to compare with sulfonated PEEK and Nafion 117 membrane. Ion-exchange capacity, water uptake, proton transport numbers and proton conductivities for different PANI composite sulfonated PEEK (SPEEK) membranes were found to be dependent on the coating density of the PANI in the membrane matrix and were slightly lower than that of Nafion 117 membrane. Methanol permeability of these membranes (especially SPEEK/PANI-1.5) was about four times lower than Nafion 117 membrane. Among the all SPEEK membranes synthesized in this study, SPEEK-1.5 appears to be more suitable for direct methanol fuel cell (DMFC) application considering optimum physicochemical and electrochemical properties, thermal stability as well as very low methanol permeability. Above all, the cost-effective and simple fabrication technique involved in the synthesis of such composite membranes makes their applicability quite attractive.     

Studies on cellulose acetate and sulfonated poly(ether ether ketone) blend ultrafiltration membranes

New ultrafiltration membranes based on chemically and thermally stable arylene main-chain polymers have been prepared by blending the sulfonated poly(ether ether ketone) with cellulose acetate in various compositions in N,N^′-dimethylformamide as solvent by phase inversion technique. Prepared membranes have been subjected to ultrafiltration characterizations such as compaction, pure water flux, water content, and membrane hydraulic resistance. The pore statistics and molecular weight cut-off (MWCO) of the membranes have been estimated using proteins such as trypsin, pepsin, egg albumin and bovine serum albumin. The pore size increased with increasing concentrations of sulfonated poly(ether ether ketone) in the casting solution. Similarly, the MWCOs of the membranes ranged from 20 to 69 kDa, depending on the various polymer compositions. Surface and cross-sectional morphologies of membranes were analyzed using scanning electron microscopy. The effects of polymer compositions on the above parameters were analyzed and the results are compared and discussed with those of pure cellulose acetate membranes.     

可逆加成-断裂链转移自由基聚合法合成梳型磺化聚醚醚酮

以带双硫酯取代基聚醚醚酮为大分子链转移剂, 采用可逆加成-断裂链转移自由基聚合(RAFT)法合成不同接枝率的磺化聚醚醚酮(g-SPEEK), 并对其结构进行表征. 在单体/链转移剂/引发剂的投料比(摩尔比)为50:4:1, 温度为70 ℃, 反应24 h, 得到聚合物膜的离子交换容量和吸水率分别为1.312 mmol/g和43.51%, 其溶胀率为5.05%, 低于Nafion膜的11.50%. 热重分析(TGA)结果表明该梳型g-SPEEK具有较好的热力学稳定性, 且该聚合物膜具有与Nafion膜相当的抗氧化性. 在相同的离子交换容量下, 梳型g-SPEEK比主链型SPEEK具有更好的H⁺离子透过性能.     

Sulfonated poly(ether sulfone)/sulfonated polybenzimidazole blend membrane for fuel cell applications

Polymer blending is used to modify or improve the dimensional and thermal stability of any two different polymers or copolymers. In this study, both sulfonated polybenzimidazole homopolymer (MS-p-PBI 100) and sulfonated poly(aryl ether benzimidazole) copolymers (MS-p-PBI 50, 60, 70, 80, 90) were successfully synthesized from commercially available monomers. The chemical structure and thermal stability of these polymers was characterized by ¹H NMR, FT-IR and TGA techniques. Blend membranes (BMs) were prepared from the salt forms of sulfonated poly(ether sulfone) (PES 70) and MS-p-PBI 100 using dimethylacetamide (DMAc). These blend membranes exhibited good stability in boiling water. The blending of 1 wt.% of MS-p-PBI 100 and 99 wt.% of PES 70 to produce the blend membrane BM 1 reduced membrane swelling, thus leading to good dimensional stability and comparable proton conductivity. Hence, BM 1 was chosen for the fabrication of a membrane electrode assembly (MEA) for proton exchange membrane fuel cell (PEMFC) and direct methanol fuel cell (DMFC) applications. This paper reports on PEMFC and DMFC performance under specific conditions.     

Sulfonated Poly(ether ether ketone) and Poly(ethylene glycol) Diacrylate Based Semi-Interpenetrating Network Membranes for Fuel Cells

Polymer electrolyte membranes are prepared from novel semi-interpenetrating polymer network material where the sulfonated poly (ether ether ketone) (SPEEK) is the linear polymer and the poly (ethylene glycol) diacrylate (PEGDA) is the cross-linking constituent. The semi-IPN is prepared by in situ polymerization of PEGDA in the presence of sulfonated poly (ether ether ketone). SPEEK is prepared by direct sulfonation of commercial PEEK (Gatone? 1100) by reported procedures. SPEEK with degree of sulfonation 63% (calculated from FT-NMR) is selected as the base membrane and different semi-IPN membranes were prepared by varying the PEGDA and SPEEK ratio. The degree of sulfonation of SPEEK and the formation of semi-IPN were confirmed by spectroscopy studies. The various semi-IPN membranes were characterized for ion-exchange capacity, water uptake, hydrolytic stability, proton conductivity and thermal stability for evaluating the suitability of these membranes for fuel cells. The proton conductivity of the membranes decreased with increasing PEGDA content. The Semi-IPN membranes exhibited conductivities (30°C) from 0.018 S/cm to 0.006 S/cm. These interpenetrating network membranes showed higher hydrolytic stability than the pure SPEEK membrane. This study shows that semi-IPN membranes based on PEGDA and SPEEK can be viable candidates for electrolyte membranes.     

A new catalyst layer based on in situ pore generation of sulfonated poly(ether ether ketone) for PEMFC

A new concept of in situ pore generation to reduce water flooding in cathode catalyst layer (CCL) of polymer electrolyte membrane fuel cell (PEMFC) is proposed with the introduction of water soluble poly(ethylene glycol) (PEG) as a porogen to CCL based on sulfonated poly(ether ether ketone) (sPEEK). In this new type of CCL, PEG is directly removed by water produced during the cathode reaction. The new CCL exhibited much higher cell performance especially in mass transport limitation region compared to the pristine sPEEK-CCL. In addition, the presence of PEG in the new CCL lowered the glass transition temperature of the sPEEK binder, and it could improve the transference of catalyst layer onto the polymer electrolyte membrane.     

Synthesis of the block sulfonated poly(ether ether ketone)s (S-PEEKs) materials for proton exchange membrane

To improve the proton conductivity of sulfonated poly(ether ether ketone)s (SPEEK) with low sulfonated degrees, a series of block SPEEK copolymers were prepared by a two-stage one pot process: first the hydrophobic block was prepared with the desired length, then the monomers for the hydrophilic block were added to the first reactive flask to form block copolymers. Membranes were cast from their DMF solutions, and characterized by determining the ion-exchange capacity, water uptake, proton conductivity and mechanical properties. Block-3 with the longer hydrophobic chain shows enhanced performance than the random one in usage for PEM. SAXS was employed to investigate the microstructure effects on the above properties. Larger ionic cluster size and larger proton transport channel in block-3 SPEEK membranes are detected from the result of SAXS. It is believed that this microstructure feature attributes to the enhanced proton conductivity values of block-3 membrane at low IEC.     

Sulfonated montmorillonite/sulfonated poly(ether ether ketone) (SMMT/SPEEK) nanocomposite membrane for direct methanol fuel cells (DMFCs)

A nanocomposite membrane of sulfonated montmorillonite/sulfonated poly(ether ether ketone) (SMMT/SPEEK) is proposed for direct methanol fuel cells (DMFCs). The SMMT is clay modified with silane of which the structure consists of a sulfonic acid group for proton conductivity improvement. The micro- and nano-scaled morphologies of the membranes perform the increase in inorganic aggregation with SMMT loading content as confirmed by SEM and AFM. The membrane stability, i.e., the liquid uptake in water and in methanol aqueous solution, as well as the mechanical stability increases with the SMMT loading content whereas thermal stability does not improve significantly. The methanol permeability reduction is obtained when the SMMT loading content increases for various methanol concentrations (1.5–4.5 M). A comparative study of the SPEEK nanocomposite membranes with SMMT and with pristine MMT shows fourfold proton conductivity enhancement after sulfonation. The DMFC single cell tests inform us that all nanocomposite membranes give the significant performance revealed by the plot of current density–voltage and power density.     

Understanding properties of copoly(arylene ether nitrile)s high-performance polymer electrolyte membranes for fuel cells from molecular dynamics simulations

Sulfonated poly(arylene ether ether nitrile) (m-SPAEEN) copolymers are reported to have the property of reduced water uptake compared with other hydrocarbon membranes, such as sulfonated polysulfones or polyketones, with similar ion exchange capacity. It is believed that this difference is largely due to the nitrile group. In this study, to investigate the effect of the nitrile group on properties of polymer electrolyte membranes for fuel cell applications, we carried out a series of molecular dynamics (MD) simulations. We compared the results of MD simulations for m-SPAEEN and sulfonated poly(arylene ether sulfone)s (BPSH). We found that water molecules hydrate not only the sulfonate (SO₃ ^?) groups of m-SPAEEN but also other hydrophilic functional groups in the copolymers. Results showed that hydration around the nitrile group in m-SPAEEN and around the sulfone (SO₂) group in BPSH differs in features related to water uptake: The former exhibits uptake of fewer water molecules than does the latter. This difference in hydration features causes m-SPAEEN to have a relatively low water-uptake level compared with BPSH.     

Polyaniline decorated graphene oxide on sulfonated poly(ether ether ketone) membrane for direct methanol fuel cells application

In direct methanol fuel cells (DMFC), methanol crossover is a major issue which has reduced the performance of polymer electrolyte membrane (PEM) for energy generation. In this study, graphene oxide (GO) and conductive polyaniline decorated GO (PANI-GO) were used as additives in fabrication of sulfonated poly(ether ether ketone) (SPEEK) nanocomposite PEM membrane to reduce methanol crossover. PANI-GO was synthesized by in situ polymerization method and the formation of PANI coated GO nanostructures was confirmed by surface morphology and crystallinity analysis. The membrane morphology and topography analysis confirmed that GO and PANI-GO were well dispersed on the surface of SPEEK membrane. 0.1 wt% PANI-GO modified SPEEK nanocomposite membrane exhibited the highest water uptake and ion exchange capacity of 40% and 1.74 meq g^?1, respectively. The oxidative stability of the nanocomposite membranes also improved. Lower methanol permeability of 4.33 × 10^?7 cm^?2S^?1 was noticed for 0.1 wt% PANI-GO modified SPEEK membrane. PANI-GO modified SPEEK membrane enhanced the proton conductivity, which was due to the existence of acidic and hydrophilic group present in PANI and GO. PANI-GO modified SPEEK membrane held higher selectivity of 1.94 × 10⁴ S cm^?3 s^?1. Overall, these studies revealed that PANI-GO modified SPEEK membrane is a potential material for DMFC applications.     

Sulfonated poly(ether sulfone)s with binaphthyl units as proton exchange membranes for fuel cell application

Sulfonated poly(ether sulfone)s containing binaphthyl units (BNSHs) were successfully prepared for fuel cell application. BNSHs, which have very simple structures, were easily synthesized by postsulfonation of poly(1,1′‐dinaphthyl ether phenyl sulfone)s and gave tough, flexible, and transparent membranes by solvent casting. The BNSH membranes showed low water uptake compared to a typical sulfonated poly(ether ether sulfone) (BPSH‐40) membrane with a similar ion exchange capacity (IEC) value and water insolubility, even with a high IEC values of 3.19 mequiv/g because of their rigid and bulky structures. The BNSH‐100 membrane (IEC = 3.19 mequiv/g) exhibited excellent proton conductivity, which was comparable to or even higher than that of Nafion 117, over a range of 30–95% relative humidity (RH). The excellent proton conductivity, especially under low RH conditions, suggests that the BNSH‐100 membrane has excellent proton paths because of its high IEC value, and water insolubility due to the high hydrophobicity of the binaphthyl structure. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5827–5834, 2009     

A Bayesian method for construction of Markov models to describe dynamics on various time-scales

The dynamics of many biological processes of interest, such as the folding of a protein, are slow and complicated enough that a single molecular dynamics simulation trajectory of the entire process is difficult to obtain in any reasonable amount of time. Moreover, one such simulation may not be sufficient to develop an understanding of the mechanism of the process, and multiple simulations may be necessary. One approach to circumvent this computational barrier is the use of Markov state models. These models are useful because they can be constructed using data from a large number of shorter simulations instead of a single long simulation. This paper presents a new Bayesian method for the construction of Markov models from simulation data. A Markov model is specified by (τ,P,T), where τ is the mesoscopic time step, P is a partition of configuration space into mesostates, and T is an N(P)×N(P) transition rate matrix for transitions between the mesostates in one mesoscopic time step, where N(P) is the number of mesostates in P. The method presented here is different from previous Bayesian methods in several ways. (1) The method uses Bayesian analysis to determine the partition as well as the transition probabilities. (2) The method allows the construction of a Markov model for any chosen mesoscopic time-scale τ. (3) It constructs Markov models for which the diagonal elements of T are all equal to or greater than 0.5. Such a model will be called a "consistent mesoscopic Markov model" (CMMM). Such models have important advantages for providing an understanding of the dynamics on a mesoscopic time-scale. The Bayesian method uses simulation data to find a posterior probability distribution for (P,T) for any chosen τ. This distribution can be regarded as the Bayesian probability that the kinetics observed in the atomistic simulation data on the mesoscopic time-scale τ was generated by the CMMM specified by (P,T). An optimization algorithm is used to find the most probable CMMM for the chosen mesoscopic time step. We applied this method of Markov model construction to several toy systems (random walks in one and two dimensions) as well as the dynamics of alanine dipeptide in water. The resulting Markov state models were indeed successful in capturing the dynamics of our test systems on a variety of mesoscopic time-scales.     

质子交换膜用磺化聚芳醚的合成与性能研究

合成了一种用于质子交换膜的新型磺化聚芳醚. 由于特殊单体结构的设计, 在聚合物主链上引入取代基对主链进行保护, 用氯磺酸直接磺化方法在聚芳醚高分子侧基上引入磺酸功能基, 实现了聚合物磺化结构的可控定位合成, 得到了稳定性较好的磺化聚芳醚. 用溶液浇膜法制备了质子交换膜, 考察了质子交换膜的各种性能. 结果表明, 这种膜具有良好的成膜性, 水解性稳定性和优异热稳定性能, 5%的热失重温度为362.3 ℃. 氧化稳定性在80 ℃的Fenton’s试剂(3%的过氧化氢和2 mg/L的FeSO₄)中进行, 膜在69 min时才开始变碎, 表现出良好的氧化稳定性.