Outstanding Oxidative Stability Research Articles

Long-life potassium metal batteries enabled by anion-derived solid electrolyte interphase using concentrated ionic liquid electrolytes

Potassium metal batteries (PMBs) show great potential as next-generation energy storage systems yet face challenges such as the dendritic growth of the potassium anode, leading to issues with cycle life and safety. This study reports a potassium salt-concentrated ionic liquid electrolyte (PCIL) consisting of potassium bis(fluorosulfonyl)imide (KFSI) and 1-methyl-1-propyl pyrrolidinium bis(fluorosulfonyl)imide (Pyr13FSI) to achieve long-life and, safe PMBs. PCIL presents several advantages including outstanding oxidation stability (≈5.2 V), decent ionic conductivity (4.0 mS cm−1 at 25 °C), and negligible flammability. Moreover, PCIL promotes the development of anion-derived solid-electrolyte interphase (SEI) with high inorganic content. This not only hinders the growth of potassium dendrites but also facilitates facile interfacial charge transfer kinetics. Benefiting from these advantages, PMBs (K||KVPO4F) employing PCIL exhibit remarkable cycle performances at both ambient and elevated temperatures (capacity retention after 300 cycles: 74.8% at 25 °C and 82.9% at 45 °C), surpassing the performance of conventional carbonate (1 M KPF6 EC/PC) and dilute potassium ionic liquid electrolyte (PIL). This work demonstrates the tangible capability of PCIL in realizing practical PMBs.

Random sulfonated poly(arylene ether sulfone) and sulfonated poly(arylene ether ketone) membranes for fuel cell applications

AbstractIn this study, sulfonated poly(arylene ether sulfone) (SPAES) and sulfonated poly(arylene ether ketone) (SPAEK) were randomly synthesized, employing a presulfonation process. This presulfonation process resulted in a more controlled and reproducible sulfonation level. The respective polymers were prepared using 2,2‐Bis(4‐hydroxyphenyl) propane at 50% molar ratio, which also provided some membrane elasticity. The resulting polymers, each had 25% of the block containing the sulfonic domains (SPAES A 25 and SPAEK A 25). Better conductive membranes were achieved for the random sulfone polymers than for the random ketone polymers, with values, respectively, of 0.24 and 0.07 S cm−1 at 80°C. The lower proton conductivity from the ketone‐based polymer was compensated with very low methanol permeability (0.25 × 10−6 cm2 s−1) and outstanding oxidative stability. The selectivity of both polymer membranes exceeded the reported values for the state‐of‐the‐art Nafion® 117 and other commercially available options. Both polymer membranes, with their unique combination of ionic domains, elastomeric blocks, and resulting morphology, could be viable candidates for fuel cell applications.

Ce–Mn bimetallic oxide-doped SPEEK/SPPO blend composite membranes to induce high oxidative tolerance and proton conductivity for hydrogen fuel cells

Utilizing CeMnOx bimetallic oxide as fillers in SPEEK/SPPO blend polymer backbone demonstrated outstanding oxidative stability and improved performance in PEMFCs.

Thermo-Mechanical Stability of Hydrocarbon-Based Pemion® Proton Exchange Membranes

Considering the environmental concerns about the disposal of perfluorosulfonic acid (PFSA) membranes as well as the growing interest in higher temperature operability of polymer electrolyte membrane fuel cells (PEMFCs), non-fluorinated hydrocarbon-based proton exchange membranes (PEMs) with aromatic backbones have become an increasingly active area of research. Low reactant cross-over, tunable electrochemical properties, and differentiated chemistries and potentially safer and cost-reducing synthesis procedures, are additional favourable features of hydrocarbon-based PEMs for prospective use in PEMFCs [1]. Vulnerable linking units, however, are known to be the main disadvantages of these polymers in the oxidative environment of fuel cells. During PEMFC operation, destructive radical species such as hydroxyl (HO•) are produced, causing polymer degradation and thinning in the membrane [2]. Recently, sulfo-phenylated polyphenylenes (sPPPs) have shown outstanding oxidative stability due to a polymer backbone comprising only aryl-aryl bonds, with mitigated chemical degradation in ex-situ and in-situ durability studies [3, 4]. Another concern is regarding the thermo-mechanical stability of PEMs. Thus, a systematic thermo-mechanical stability study is required to confirm the potential of sPPP-based PEMs to replace conventional PFSAs, especially for high temperature PEMFC, i.e., 110-120 °C.The present research objective is to assess the thermo-mechanical stability of a commercial reinforced hydrocarbon-based PEM, Pemion® (PF1-HLF8-15-X, 15 µm thick, reinforced), as well as a mechanically-reinforced PFSA-based reference membrane, across a wide range of temperature (30-120 °C) and relative humidity (RH) (10-90%) conditions that includes the crucial high temperature window of interest for future PEMFCs [6]. To this end, a comprehensive design of experiment yielded 19 tensile tests at various hygrothermal conditions with dynamic mechanical analyzer (DMA 850; TA Instruments) equipped with an external environmental chamber accessory (TA Instruments, RH Accessory). Important mechanical properties such as Young’s modulus, ultimate tensile stress, yield stress, maximum elongation at break, strain hardening, and modulus of resilience were extracted and discussed as well. Datapoints were fitted for empirical model development and mechanical properties were estimated for high temperature and RH conditions beyond the capability of the instrument. This method can be employed to assess if the mechanical properties of membrane materials can be retained at higher temperatures, regardless of polymer chemistry and type. Storage modulus and loss modulus were separately measured in a dynamic mode to observe the impact of temperature on the mechanical response of the hydrophobic backbone and hydrophilic ionic clusters, respectively.Overall, Pemion® demonstrates tough tensile properties in the stress-strain tests due to its sterically encumbered polyphenylene backbone (Figure 1a), whereas the reference PFSA (Figure 1b) shows elastomer-like behavior with much lower Young’s modulus, yield stress, and strain hardening (slope of the curve in the plastic deformation region). Figure 1c-f show the main viscoelastic properties extracted from the tensile tests at room (30 °C, 50% RH) and high temperature fuel cell conditions (110 °C, 50% RH). The modulus of elasticity and strain hardening of Pemion® membrane are almost temperature-independent, whereas these properties for the reinforced PFSA material undergo a significant decay at high-temperature ambience. Pemion® maintains good yielding strength even at high temperature and RH conditions (110-120 °C and 80% RH). Nevertheless, small mechanical stress values as low as 1 MPa can cause spontaneous yielding in the PFSA reference material above 110 °C. The modulus of resilience for the reinforced PFSA is also predicted to be zero at elevated hygrothermal conditions (i.e., 90 °C and 70% RH). This is interpreted as an approach to the material’s glass transition condition, where it loses its mechanical integrity and therefore, is potentially unsuitable for higher temperature PEMFC operation. Moreover, the dynamic mechanical thermal analysis revealed that Pemion® retains its robustness at hygrothermal ambience close to high-temperature PEMFCs, i.e., 110-120 °C and 40-50% RH, whereas the backbone of the PFSA material gradually loses its strength. Acknowledgements This project was financially supported by Natural Sciences and Engineering Research Council of Canada (NSERC), Ionomr Innovations Inc, Canada Foundation for Innovation (CFI), British Columbia Knowledge Development Fund (BCKDF), Western Economic Diversification Canada (WD), and Canada Research Chairs (CRC).

Interfacial interaction of graphene oxide with montmorillonite in tailoring the structure and proton transport phenomena of alginate/PVA membrane for DMFC applications

AbstractPolymer electrolyte membrane that has high proton conductivity and low methanol permeability are necessary for direct methanol fuel cells (DMFCs). A sodium alginate (SA)/polyvinyl alcohol (PVA)/montmorillonite (MMT)/graphene oxide (GO) quaternary composite membrane was effectively developed in this study. The homogeneous distribution of MMT and GO nanosheets in the SA/PVA/MMT/GO composite membrane was exhibited by scanning electron microscopy (SEM). Intriguingly, it has been established that the SA/PVA membrane contains chemical crosslinks between MMT and GO, which significantly contribute to the rise in proton conductivity. The SA/PVA/MMT/GO hybrid membrane has minimum loss modulus of 47.91% and storage modulus of up to 2.689 × 109 Pa, which are 3.8 times greater than those of SA/PVA‐MMT membrane without GO. This value indicates the viscosity and elasticity of the produced membrane. The quaternary composite membrane also exhibits outstanding oxidative stability and methanol barrier characteristics. The methanol permeability of SA/PVA/MMT/GO films 0.524 × 10−9 cm2 s−1, with methanol absorption as low as 9.72%. The best membrane performs at a high‐power density (1.761 mW/cm2) of DMFC at a GO content of 1.3 wt% because it obtains the maximum selectivity value (7.0529 × 106 S scm−3). Future commercial membranes may be replaced by the innovative quaternary membrane created in this work, which has significant potential.

Ultrastable 2D material-wrapped copper nanowires for high-performance flexible and transparent energy devices

Wrapping metallic nanomaterials with two-dimensional (2D) materials can significantly improve the physical properties required for various electronic and catalytic applications. However, synthesizing 2D material-wrapped metal nanowires with highly organized shell morphology is still difficult because of their large surface area and high aspect ratio. We propose a simple and practical method for synthesizing 2D material-wrapped copper nanowires (CuNWs) with highly organized shell morphology by using 2D quantum dot (QD) assembly and flash light irradiation under low temperature and non-vacuum conditions. A uniform and thin layer of QDs comprising 2D material such as graphene or hexagonal boron nitride is constructed on the CuNW by using a solution process. The 2D QD-wrapped CuNW is then subjected to flash light irradiation to realize highly organized shell morphology. Microstructural observations showed that the flash light irradiation reconstructs the shell structure and improves crystal quality without structural deformation. The 2D material-wrapped CuNWs were used to fabricate transparent conducting electrodes (TCEs) exhibited outstanding oxidation stability, chemical stability, and mechanical durability. These TCEs were applied to realize high-performance transparent supercapacitors and heaters. In particular, the transparent supercapacitors based on the graphene-wrapped CuNW TCE demonstrated excellent capacitive behavior under acidic electrolyte conditions. They showed the highest areal capacitance (18.97 mF cm−2) compared to other metal nanowire-based transparent supercapacitors. Finally, a novel method for fabricating carbon and boron nitride nanotubes by wet-etching the core CuNW of the 2D material-wrapped CuNWs was successfully developed.

In-situ construction of dual lithium-ion migration channels in polymer electrolytes for lithium metal batteries

Solid polymer electrolytes (SPEs) are expected to play an important role in high-energy lithium metal batteries (LMBs). Unfortunately, SPEs suffer from inadequate room-temperature ionic conductivity and sluggish interfacial charge transport, which severely limit their widespread applications in LMBs. Herein, we in-situ construct dual lithium-ion migration channels based SPEs by combining ring-opening polymerization of 1,3-dioxolane and solid-state organic ionic plastic crystals. “Coordination-dissociation” with the oxygen atoms in polymer chain segments and fast ion migration inside the organic ionic plastic crystal are two migration modes formed in-situ to synergistically enhance the ionic conductivity and interfacial charge transfer of SPEs. As a result, the in-situ formed poly(1,3-dioxolane)-based solid electrolytes (PDEs) not only afford an integrated battery structure with stabilized electrodes/electrolyte interface but also achieve outstanding oxidation stability, uniform lithium deposition (greater than1200 h under 0.5 mAh cm−2 in symmetric Li cells). Based on PDEs, the Li-LiFePO4 batteries demonstrate excellent cycle stability (almost no capacity decay after 500 cycles under 2C at 25 °C) and a wide operating temperature (-15 ∼ 45 °C). Also, applications of PDEs in Li-LiNi0.6Mn0.2Co0.2O2 batteries further demonstrate the compatibility of PDE with high voltage battery systems. Our study provides a facile and practical approach for creating solid electrolytes that meet both the ionic conductivity and interfacial charge transport requirements for practical solid-state batteries.

Microstructure regulation of porous polybenzimidazole proton conductive membranes for high-performance vanadium redox flow battery

As one of the important parts of vanadium redox flow battery (VRFB), the proton conductive membrane (PCM) should have high proton selectivity (PS) of H+ to VO2+ in addition to the specific properties, such as outstanding oxidative stability, long lifetime and low price. However, polybenzimidazole PCMs usually have lower proton transference resulting in lower PS. In this study, three kinds of porous poly (oxyphenylene benzimidazole) (OPBI) membrane, such as OPBI-MSA-VIPS membrane, OPBI-DMAc-VIPS membrane and OPBI-DMAc-NIPS membrane, formed respectively by vapor induced phase separation (VIPS) and non-solvent induced phase separation (NIPS) method, using methanesulfonic acid (MSA) and N,N-dimethylacetamide (DMAc) as solvent separately, are investigated to prepare a kind of high performance PCM with high PS. The OPBI-DMAc-NIPS membrane has a fingerlike microstructure with two dense skin layers. The OPBI-MSA-VIPS membrane has a uniform cellular-like microstructure with single dense skin layer, which endows the membrane's excellent vanadium resistance and high PS. The PS of OPBI-MSA-VIPS membrane is one order higher than that of OPBI-DMAc-VIPS membrane which has a spongy-like structure without dense skin layer. Furthermore, we study the effect of the polymer concentration on the structure and the corresponding battery properties of OPBI-MSA-VIPS membrane in detail. When the casting solution concentration is 6 wt % (P6 membrane)，the PS reaches the highest, about 7.74 times higher than that of commercial Nafion 115. More importantly, P6 membrane displays relatively long cycling stability. The EE value of the VRFB equipped with P6 membrane maintains stability after 3000 cycles at the current density of 160 mA/cm2. This work highlights an excellent porous OPBI membrane that has the potential to be used as high performance PCM for new energy battery.

Titanium oxide/graphitic carbon nitride nanocomposites as fillers for enhancing the performance of SPAES membranes for fuel cells

Our work deals with the fabrication of nanocomposite membranes by reinforcing sulfonated poly(aryl ether sulfone)s (SPAES) properties through incorporating various titanium oxide/graphitic carbon nitride (TiO2/g-C3N4) nanocomposite contents. They reveal promising results for applications in proton exchange membrane fuel cells. The nanocomposites introduction provides the membranes with noticeable proton conductivity, mechanical and dimensional stability improvements in comparison with the control SPAES membrane. The SPAES-TiO2/g-C3N4-1.0 nanocomposite membrane demonstrates the prominent proton conductivity of 325.3mScm−1 at 80°C and 258.4mScm−1 at 94.1% RH, as well as outstanding oxidative stability of only weight loss of 4.6% after the Fenton’s accelerating aging at 80°C for 1h. For the single fuel cell performance, it reaches the highest power density of 525.6mWcm-2 at 1150.8mAcm-2. These results suggest the good prospect of the dual compositing strategy for membrane modification in the fuel cell applications.

Synthesis and Characterization of Phenolphthalein‐Containing Sulfonated Poly(arylene ether phosphine oxide)s by Direct Polycondensation for Proton Exchange Membrane

ABSTRACTA series of novel phenolphthalein‐containing sulfonated poly(arylene ether phosphine oxide)s (sPAEPP) with various sulfonation degrees were synthesized by direct polycondensation. The structure of sPAEPP was confirmed by 1H‐NMR, 13C‐NMR, and IR spectroscopy. The high‐molecular weight of these polymers was determined by gel permeation chromatography (GPC). The transparent, tough, and flexible membranes could be achieved by solution casting. The macroscopic properties and microstructure of the obtained membranes were investigated in detail. The results showed that these sPAEPP membranes displayed excellent properties in terms of swelling, proton conductivity, and methanol permeability. For example, sPAEPP‐100 membrane exhibited an appropriate water uptake of 33.1%, a swelling ratio of only 11.7% (lower than 20.1% of Nafion 117), a proton conductivity of 0.11 S cm−1 (similar to that of Nafion 117) at 80 °C, and a methanol permeability of 4.82 × 10−7 cm2 s−1. Meanwhile, it also presented outstanding oxidative stability. Atomic force microscope (AFM) micrographs showed that the hydrophilic domains of the sPAEPP‐100 membrane formed connected and narrow ionic channels, which contributed to its high proton conductivity and good dimensional stability. As a result, sPAEPP‐100 membrane displays excellent application prospect for fuel cells. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1097–1104

Profiling and catalytic upgrading of commercial palm oil-derived biodiesel fuels for high-blend fuels

Commercial palm oil-derived biodiesel fuels (palm BDFs) were thoroughly profiled based on the specifications of international fuel standards. Their main components were found to be fatty acid methyl esters (FAME) with different numbers of double bonds in the fatty acid tails in addition to small amounts of unreactive glycerides and impurities, the concentrations of which varied slightly among the regional producers in Thailand. The fuel properties of the as-received commercial palm BDFs met international fuel standards; unfortunately, the fuel degraded significantly over time, presumably due to the presence of polyunsaturated fatty acid methyl esters (poly-FAME) and impurities. To prevent this degradation, the commercial palm BDFs were upgraded into partially hydrogenated fatty acid methyl esters with outstanding oxidation stability (H-FAME, a new type of biodiesel fuel enriched in monounsaturated fatty acid methyl esters (mono-FAME)) over supported Pd catalysts with metallic Pd nanoparticles as the catalytically active sites in a batch-type glass reactor under mild conditions (80 °C and 0.5 MPa H2). In the upgrading process, the unwanted component poly-FAME, which had low oxidation stability, was selectively converted into the target component, mono-FAME with high oxidation stability. Although the impurities in the commercial palm BDFs poisoned the supported Pd catalysts, particularly the sulfur species, the homemade mesoporous silica-supported Pd catalyst with a high Pd dispersion of 47% gave higher activity and tolerance to the impurities in the synthesis of palm H-FAMEs than the commercial alumina-supported Pd catalyst, which had a low Pd dispersion of 16%. In the accelerated oxidation stability test, the B20 fuels formulated by blending petro-diesel with the palm H-FAMEs with enhanced oxidation stability produced almost no deposits or sludges, whereas the fuels formulated by blending petro-diesel with commercial palm BDFs were seriously degraded and acidified, and formed deposits and sludges. Moreover, the palm H-FAMEs could be further purified by selective removal of the monoglycerides (MG) and steryl glucosides (SG) through wintering and adsorption posttreatments, and were determined to be a reliable BDF source with high safety and security for use in high blend fuels.

Comparison of the effect of Pleurotus citrinopileatus extract and vitamin E on the stabilization properties of camellia oil

We selected Camellia tenuifolia (Hayata) seed oil to compare the effects of mushroom extract and vitamin E on its stabilization properties. Camellia tenuifolia was selected for its higher oil content, but its proportions of unsaturated fatty acids and natural antioxidants as well as its oxidation stability are lower than those of Camellia oleifera oil. Our aim was to improve the oxidation stability, thermal stability, and photodegradation of C. tenuifolia seed oil and then compare the advantages of mixing traditional antioxidant (vitamin E) and mushroom natural antioxidant components (mushroom extract) in the oil. The focus was on the analysis of the effects of Pleurotus citrinopileatus (Singer) extract and vitamin E on the stabilization properties of C. tenuifolia seed oil, which involved some degradation research, such as evaluating the thermal, oxidation, and antioxidant effects as well as the irradiative (pulsed light) stability of the original oil and oil mixed with additives for comparing the differences by differential scanning calorimetry tests and isothermal microcalorimeter (TAM Air) analyses. We determined the effects of stabilization additives vitamin E and various PC extract doses by using pulsed light irradiation (0, 30, and 60 pulses) and found that the 3 mass% PC extract had the best antiphotodegradation characteristics, and the 0.1 mass% vitamin E indicated the outstanding oxidation stability for among all of the additives in this study. Overall, we obtained the following suitable conditions to stabilize camellia oil: addition of vitamin E, addition of 3 mass% PC extract, and a nitrogen atmosphere.

Fabrication of sulfonated poly(aryl ether ketone sulfone) membranes blended with phosphotungstic acid and microporous poly(vinylidene fluoride) as a depository for direct-methanol fuel cells

A series of sulfonated poly(aryl ether ketone sulfone)/poly(vinylidene fluoride) phosphotungstic acid (SPAEKS/PVDF-HPW) composite membranes were prepared and characterized by Fourier transform infrared spectroscopy. No phase separation was observed by scanning electron microscopy. The HPW particles are evenly dispersed in the membranes, probably because the microporous structure of PVDF stabilized the dispersion of HPW particles in the membranes. Thermogravimetric analysis showed that the thermal stability of the membranes increased with increase in HPW content. Moreover, the composite membranes exhibited outstanding oxidative stability. The methanol permeability coefficient of the SPAEKS/PVDF-HPW10% membrane at 20 °C was 1.68 × 10−7 cm2 s−1, and the highest proton conductivity of the membrane at 80 °C was 0.098 S cm−1, slightly lower than that of Nafion® 117. However, the relative selectivity of the membrane was higher than that of Nafion® 117. The swelling ratio of the membrane at 80 °C was 16%, and the methanol uptake of the membrane at room temperature was only 10.2%, much lower than those of Nafion® 117. The results indicate that the SPAEKS/PVDF-HPW membranes can be used as an alternative proton exchange membrane for direct-methanol fuel cells.

Flexible transparent conducting hybrid film using a surface-embedded copper nanowire network: a highly oxidation-resistant copper nanowire electrode for flexible optoelectronics.

We report a flexible high-performance conducting film using an embedded copper nanowire transparent conducting electrode; this material can be used as a transparent electrode platform for typical flexible optoelectronic devices. The monolithic composite structure of our transparent conducting film enables simultaneously an outstanding oxidation stability of the copper nanowire network (14 d at 80 °C), an exceptionally smooth surface topography (R(rms) < 2 nm), and an excellent opto-electrical performances (Rsh = 25 Ω sq(-1) and T = 82%). A flexible organic light emitting diode device is fabricated on the transparent conducting film to demonstrate its potential as a flexible copper nanowire electrode platform.

Sulfonated Poly(arylene ether phosphine oxide ketone) Block Copolymers as Oxidatively Stable Proton Conductive Membranes

The introduction of triphenylphosphine oxide moiety into the hydrophilic segments of aromatic multiblock copolymers provided outstanding oxidative stability and high proton conductivity. Our designed multiblock copolymers are composed of highly sulfonated phenylene ether phosphine oxide ketone units as hydrophilic blocks and phenylene ether biphenylene sulfone units as hydrophobic blocks. High molecular weight block copolymers (Mw = 204-309 kDa and Mn = 72-94 kDa) with different copolymer compositions (number of repeat unit in the hydrophobic blocks, X = 30, and that of hydrophilic blocks, Y = 4, 6, or 8) were synthesized, resulting in self-standing, transparent, and bendable membranes by solution-casting. The block copolymer membranes exhibited well-developed hydrophilic/hydrophobic phase separation, high proton conductivity, and excellent oxidative stability due to the highly sulfonated hydrophilic blocks, which contained phenylene rings with sulfonic acid groups and electron-withdrawing phosphine oxide or ketone groups.

Sulfonated poly(arylene ether)s with high content of phosphine oxide moieties for proton exchange membranes

Sulfonated poly(arylene ether)s with high content of phosphine oxide moieties were achieved by polycondensation of bis(4-hydroxyphenyl)phenyl phosphine oxide with sulfonated bis(4-fluorodiphenyl)phenyl phosphine oxide and bis(4-fluorophenyl)phenyl phosphine oxide (or decafluorobiphenyl) for the first time. The high content phosphine-oxide moieties are expected to improve the oxidative stability of membranes, while the decafluorobiphenyl units were used to depress the swelling. The studies illustrated that all these membranes exhibited outstanding oxidative stability because of high content phosphine oxide moieties. On the other hand, the membranes with decafluorobiphenyl moieties (sPEPOF) displayed low swelling. This originates from these hydrophobic groups because they facilitated the membranes to form narrow ionic clusters. In summary, the sPEPOF membranes exhibited excellent overall properties. For instance, the sPEPOF membrane with 80% sulfonation degree displayed a proton conductivity of 0.077 S/cm as well as a swelling of 12% at 80 °C. It also exhibited outstanding oxidative stability and high thermal stability.

Synthesis and characterization of sulfonated poly(arylene ether ketone/ketone phosphine oxide)s as proton exchange membranes

Sulfonated poly(arylene ether ketone phosphine oxide)s (sPEKP) and sulfonated poly(arylene ether ketone ketone phosphine oxide)s (sPEKKP) were prepared by polycondensation for the first time. The phosphine oxide moieties in products were expected to enhance water retention and improve the overall properties. Their properties as proton exchange membranes were investigated and compared. They all showed high thermal stability. Moreover, the sPEKP membranes showed low swelling though they have considerable water uptake at 80 °C. However, the sPEKKP membranes displayed much higher water uptake and swelling than the sPEKP membranes with an equivalent ion exchange capacity (IEC) at elevated temperatures, which is due to the structural difference between them. More importantly, the sPEKP and sPEKKP membranes indicated outstanding oxidative stability because of the passivation effect of phosphine oxide groups. In short, the sPEKP membranes showed good overall properties. For example, sPEKP-400 not only showed high thermal and oxidative stability, but also displayed a swelling of 21% and a proton conductivity of 0.075 S/cm at 80 °C.

The thermo-oxidative degradation of metallocene polyethylenes. Part 1: Long-term thermal oxidation in the solid state

The long-term thermo-oxidative degradation of different metallocene polyethylenes (mPEs) was investigated in the solid state (oven ageing in air at 90 °C). The mPEs differed essentially according to their initial melt index, molar mass distribution, density and ash content. Two Phillips-type HDPEs were also studied for comparison. The rate of oxidation was assessed by carbonyl index measurements. Initial vinyl unsaturation and short chain branch contents were correlated with induction times. The hydroperoxide concentrations of the aged materials and the levels of metal catalyst residues were also evaluated. Outstanding oxidative stability was exhibited for all the mPEs in the solid state relative to the Phillips HDPEs. This was believed to be due to the low concentration of both adventitious metal catalyst residues and initial vinyl unsaturation. Degree of short chain branching also appeared to influence the oxidative stability of the mPEs. Besides inherent properties, the density/crystallinity appeared to be the main factor influencing their oxidative stability. In the case of the Phillips HDPEs, the high level of vinyl unsaturation together with chromium catalyst residues may contribute to their poor oxidative stability.