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The consequence of coupling wear (erosion/abrasion) and corrosion is not just simply the sum of wear in the absence of corrosive medium and corrosion in absence of wear. The so-called synergistic effect implies that corrosion is accelerated due to the removal of the passivating layer because of wear. On the other hand, corrosion can accelerate abrasion when the electrochemical dissolution yields a brittle surface layer which can be subsequently removed by abrasion. The synergism between wear and corrosion is complex and the interaction between mechanical and chemical factors governing tribocorrosion is not yet fully understood. This review aims at providing a general and thorough summary of the wear-corrosion interaction focused on stainless steels due to the technological relevance of these materials. It is taken into consideration the influence of the key parameters affecting wear-corrosion, such as the stainless steel type, slurry characteristics (temperature, pH, solid concentration), the erodent properties (particle size and shape), etc. The different models to describe wear-corrosion and the most used apparatus for tribocorrosion testing are also reviewed.

Natrium super ionic conductor (NASICON) materials providing attractive properties such as high ionic conductivity and good structural stability are considered as very promising materials for use as electrodes for lithium- and sodium-ion batteries. Herein, a new high-performance electrode material, Li0.5Ni0.5Ti1.5Fe0.5(PO4)3/C, was synthesized via the sol-gel method and was electrochemically tested as an anode for lithium ion batteries, providing enhanced electrochemical performance as a result of nickel substitution into the lithium site in the LiTi2(PO4)3 family of materials. The synthesized material showed good ionic conductivity, excellent structural stability, stable long-term cycling performance, and improved high rate cycling performance compared to LiTi2(PO4)3. The Li0.5Ni0.5Ti1.5Fe0.5(PO4)3/C electrode delivered reversible capacities of about 93 and 68% of its theoretical one at current rates of 0.1 C (6.42 mA·g-1) after 100 cycles and 5 C (320.93 mA·g-1) after 1000 cycles, respectively. Theoretically, three Li+ ions can be inserted into the vacancies of the Li0.5Ni0.5Ti1.5Fe0.5(PO4)3/C structure. However, when the electrode is discharged to 0.5 V, more than three Li+ ions are inserted into the NASICON structure, leading to its structural transformation, and thus to an irreversible electrochemical behavior after the first discharge process.

A novel radiation grafted ETFE based proton conducting membrane was prepared by double irradiation grafting of two different monomers. The intrinsic oxidative stability of the ETFE-g-poly(styrene sulfonic acid-co-divinylbenzene) membrane was improved by reducing the gas crossover through incorporation of polymethacrylonitrile (PMAN) containing the strong polar nitrile group. A fuel cell test was carried out at 80 °C under constant current density of 500 mA cm−2 for a time exceeding 1′900 h. The incorporation of PMAN considerably improves the interfacial properties of the membrane-electrode assembly. No significant change in the membrane hydrogen crossover and performance over the testing time was observed, except for a measured decrease in the membrane ohmic resistance after 1′000 h. The combination of the double irradiation induced grafting with the use of the PMAN as gas barrier in addition to its chelating abilities (e. g. Ce3+) offers a promising strategy to develop more durable membranes for fuel cells.

International audience; A composite based on hydroxyapatite (HA) and chitosan (CS) combined with ciprofloxacin (CIP) was formulated by the solid-liquid mixing method. The optimization of the solid to the liquid ratio and the use of chitosan in a small amount (

Alfa fibers (Stipa Tenacissima) were effectively utilized in this study as a promising cellulose source for isolation of carboxy-functionalized cellulose nanofibrils (CNFs) using multiple treatments. Pure cellulose microfibers (CMFs) were firstly extracted by alkali and bleaching treatments. CNFs with an average nanofibrils diameter ranging from 1.4 to 4.6 nm and a crystallinity of 89% were isolated from CMFs by a combination of TEMPO-oxidation and mechanical disintegration processes. The morphology and physico-chemical properties of cellulosic materials were evaluated at different stages of treatments using several characterization techniques. Various CNF loadings (5–15 wt%) were incorporated into PVA polymer to evaluate the nanoreinforcement ability of CNFs and to produce CNF-filled PVA nanocomposite materials. The tensile and optical transmittance properties, as well as the morphological and thermal properties of the as-produced CNF-filled PVA nanocomposite films were investigated. It was found that the tensile modulus and strength of nanocomposites were gradually increased with increasing of CNF loadings, with a maximum increase of 90% and 74% was observed for a PVA nanocomposite containing 15 wt% CNFs, respectively. The optical transmittance was reduced from 91% (at 650 nm) for neat PVA polymer to 88%, 82% and 76% for PVA nanocomposites containing 5, 10 and 15 wt% CNFs, respectively. It was also found that the glass transition temperature was gradually increased from 76 °C for neat PVA to 89 °C for PVA nanocomposite containing 15 wt%. This study demonstrates the importance of Alfa fibers as annual renewable lignocellulosic material to produce CNFs with good morphology and excellent properties. These newly developed carboxy-functionalized CNFs could be considered as a potential nanofiller candidate for the preparation of nanocomposite materials of high transparency and good mechanical properties.

This work investigates the isolation of cellulose nanocrystals (CNC) from sugarcane bagasse (SCB) waste and the evaluation of their mechanical reinforcement capability for k-carrageenan biopolymer. The results from Atomic Force Microscopy and Transmission Electron Microscopy indicated the successful extraction of CNC from SCB following alkali, bleaching and acid hydrolysis treatments. The CNC displayed a needle-like structure with an average aspect ratio of 55. The surface functionality of the CNC was evaluated by Fourier Transform Infrared Spectroscopy and X-ray Photoelectron Spectroscopy measurements. X-ray diffraction studies showed that the as-extracted CNC exhibit cellulose I crystalline structure, with a crystallinity index of 80%. The obtained CNC were dispersed into k-carrageenan biopolymer matrix at various CNC contents (1, 3, 5 and 8 wt%) and the prepared films were further characterized. The incorporation of CNC decreased the light transmittance values but enhanced the mechanical properties compared with the neat k-carrageenan film. Empirical Halpin-Tsai model was used to predict the CNC dispersion within k-carrageenan matrix. The obtained nanocomposite films have the potential to be used as food packaging material.

This work reports on the preparation of oil-filled microcapsules for self-healing purposes. Biopolymeric microcapsules loaded with vegetable oils as green corrosion inhibitors were formulated using ethyl cellulose and phosphorylated ethyl cellulose as encapsulating materials. Chemical structure, thermal stability and surface morphology of microcapsules were characterized by Fourier transform infrared (FTIR) spectroscopy, thermal gravimetric analysis (TGA) and scanning electron microscopy (SEM). FTIR and TGA analysis confirmed the presence of oil core and polymer shell in the formulated microcapsules. The scanning electron microscopy was used to evaluate the shape and morphology of the prepared microcapsules. The obtained results revealed the spherical-like shape of the obtained capsules with diameters ranging from 10 up to 170 µm. Thus, the current study shows the potential application of phosphorylated ethyl cellulose for the development of new environmentally friendly microcontainers bearing corrosion inhibitors for end use in anti-corrosion self-healing coatings.

This study reports for the first time the preparation of almond oil-based microcapsules using phosphorylated ethyl cellulose as shell material. Microcapsules of ethyl cellulose (EC) and phosphorylated ethyl cellulose (P-EC) containing almond oil as anti-corrosion inhibitor, for end use in self-healing coatings, were prepared by a solvent evaporation method. The results showed that phosphorus content in the modified ethyl cellulose was 6.26 wt.%, the specific surface area reached a high value of 21.4 m2 g−1 and a char residue of 18 wt.% at 400 °C after thermal degradation. Both prepared EC and P-EC based microcapsules were spherical shape-like. The scanning electron microscope (SEM) images showed that the freeze-drying influences the microcapsules surface morphology. The mean diameter of EC and P-EC microcapsules was about 140 μm and 150 μm, respectively. Anti-corrosion properties of prepared epoxy-based coatings loaded with microcapsules on the mild steel substrate were evaluated for 28 days using a simple salt spray test. The sample containing P-EC microcapsules showed the best anticorrosion resistance. The functionalization of the ethyl cellulose microcapsules shell with phosphonate groups can improve further the anti-corrosion resistance, the flame-retardant ability and the metal chelating properties of the final coatings.

In the present work, cellulose nanocrystals (CNC) were produced from vine shoots waste using chemical treatments followed by acid hydrolysis process. FTIR analysis confirmed that the non-cellulosic components were progressively removed during the chemical treatments, and the final obtained materials are composed of pure cellulose. AFM and TEM observations showed that the extracted CNC possess a needle-like shape with an average length of 456 nm and an average diameter of 14 nm, giving rise to an average aspect ratio of about 32. The as-extracted CNC exhibit a cellulose I structure with high crystallinity index (82%), as determined by XRD characterization. Importantly, the resulted CNC provide a higher thermal stability in comparison with CNC extracted from other resources, using the same extraction process. The isolated CNC's surface charge density was evaluated by XPS analysis and resulted in ~2.0 sulfate groups per 100 anhydroglucose units. In order to identify the reinforcing ability of the new extracted CNC, Carboxymethyl cellulose nanocomposite films were prepared with various CNC contents (1, 3, 5, 8 wt%) and their mechanical properties were investigated by uniaxial tensile test. The results showed that the as-extracted CNC displayed a higher reinforcing ability for nanocomposite materials.

Cellulose nanocrystals (CNC) were extracted from Miscanthus (MST) fibers using a sulfuric acid hydrolysis process. The results showed that the obtained CNC exhibit a needle-like shape with an average aspect ratio of 37. The surface charge density was measured at 1.99 sulfate groups per 100 anhydroglucose units while the zeta potential value was found to be -38 mV. The crystallinity of the extracted CNC was 76%, and the cellulose I type crystal structure was predominant. Due to its high importance for potential application of CNC in aqueous systems, the rheological behavior of CNC aqueous suspensions at various CNC concentrations was determined. The CNC suspensions showed gel-like behavior at very low CNC concentrations ranging from 0.1 wt% up to 0.6 wt%, as confirmed by the steady shear viscosity measurements and the oscillatory dynamic tests. The dynamic rheological parameters of CNC suspensions were slightly affected by the temperature profile. At high temperature up to 80 °C a stronger CNC network is formed by increasing the relative motion resistance of CNC macromolecules and the entanglement. In order to identify the reinforcing ability of the newly extracted CNC, starch-based nanocomposite films were produced with various CNC contents (1, 3, 5 and 8 wt%) and their tensile properties were investigated. It was found that the addition 8 wt% CNC within starch matrix increased the Young’s modulus by 150% and the tensile strength by 118%, resulting in mechanically strong and eco-friendly nanocomposite materials.

Inverse vulcanization copolymers (p(S-DVB)) from the radical polymerization of elemental sulfur and divinylbenzene (DVB) have been studied as cathode active materials in poly(ethylene oxide) (PEO)-based all-solid-state Li-S cells. The Li-S cell comprising the optimized p(S-DVB) cathode (80:20 w/w S/DVB ratio) and lithium bis(fluorosulfonyl)imide/PEO (LiFSI/PEO) electrolyte shows high specific capacity (ca. 800 mAh g −1 ) and high Coulombic efficiency for 50 cycles. Most importantly, polysulfide (PS) shuttle is highly mitigated due to the strong interactions of PS species with polymer backbone in p(S-DVB). This is demonstrated by the stable cycling of the p(S-DVB)-based cell using lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)/PEO electrolyte, where successful charging cannot be achieved even at the first cycle with plain elemental S-based cathode material due to the severe PS shuttle phenomenon. These results suggest that inverse vulcanization copolymers are promising alternatives to elemental sulfur for enhancing the electrochemical performance of PEO-based all-solid-state Li-S cells.

Carboxymethyl chitin (CMChit) has the potential to be used as a solid polymer electrolyte (SPE) based on its ionic conductivity value of the order of 10−6 S·cm−1 in self-standing membranes. In controlled humidity of 65RH%, carboxymethyl chitin based membrane blended with 1-Butyl-3-methylimidazolium acetate (BMIM[Ac]) ionic liquid (IL) (40 wt%) showed a threshold value of ionic conductivity in the order of 10−4 S·cm−1 and electrochemical stability was up to 2.93 V. The effects of the relative humidity and ionic liquid weight fraction on the ionic conductivity and structural changes were investigated in detail. Furthermore, the X-ray diffraction (XRD) diffractogram indicated a clear reduction of crystallinity of the CMChit. The Field-emission scanning electron microscopy (FESEM) observation of the cross-sections confirmed the homogeneity of the prepared blend. This electrolyte was tested in symmetric cells based on Zn//SPE//Zn and showed good reversibility and potential for application in proton-conducting batteries.

A correlation between the crystal structure, the ionic conductivity and the electrochemical performance in Lithium-ion batteries was established for a series of NASICON-type phosphates Li0.5M0.5Ti1.5Fe0.5(PO4)3 (M = Mn, Co, Mg). These electrode materials, where the M1 site contains both lithium and the divalent cation M, were prepared using a simple sol-gel process while controlling the pH and the final synthesis temperature. The three phosphates crystallize in the rhombohedral system (S.G. R-3c) with comparable unit cell parameters but with slight difference in the local distortion of the PO4 tetrahedra as confirmed by the Raman study. The ionic conductivities of the Li0.5M0.5Ti1.5Fe0.5(PO4)3 materials were measured at different temperatures using a wide range of frequencies. Mn-based phosphate shows the best features for application as electrode material for Li-ion batteries in term of the conductivity at room temperature and the activation energy of Li+ conduction process. The initial discharge capacity of 100 mAh.g − 1 was obtained for the Mg-based phosphate, 104.3 mAh.g − 1 for the Co-based material while the Mn-based material delivers the best first discharge capacity of 125.3 mAh.g − 1 with the lowest polarization in relation with its better conduction properties. This result was also confirmed by the rate capability tests where Mn-based phosphate shows enhanced electrochemical performance even at fast rate of 5C.

New synthesis route of polysalt with single ion conductivity based on functionalization of polyacrylic acid is reported for all solid state lithium metal batteries. Poly[(trifluoromethyl)sulfonyl acrylamide] PA–LiTFSI was synthesized in two steps reaction. The degree of functionalization of the polymer backbone by anion of lithium salt bis(trifluoromethane)sulfonimide (LiTFSI) was confirmed by ICP analysis. An ionic conductivity equal 1,77 10 −5 S cm −1 at 80 °C of polysalt blended with PEO is reported. Easy process-able polysalt blended with PEO exhibits good mechanical properties and high transference number.

Semi-interpenetrated network Solid Polymer Electrolytes (SPEs) were fabricated by UV-induced cross-linking of poly(ethyleneglycol) diacrylate (PEGDA) and divinylbenzene (DVB) within a poly(ethyleneoxide) (PEO) matrix (Mv = 5 × 106 g mol−1), comprising lithium bis(trifluoromethanesulfonyl)imide salt (LiTFSI), at a molar ratio of EO:Li ∼ 30:1. The influence of the DVB content on the final SPE properties was investigated in detail. An increase of DVB concentration resulted in self-standing polymer electrolytes. The DVB cross-linker incorporation was found to decrease the crystallinity of the PEO matrix from 34% to 23%, with a decrease in the melting temperature (Tm) of the membrane from 50 °C to 34 °C. Moreover, the influence of the DVB concentration on the ionic conductivity was determined for polymer electrolytes with 0, 10, 20 and 45% DVB from room temperature (RT) to 80 °C. The resulting SPEs showed a high electrochemical stability of 4.3 V as well as practical conductivity values exceeding 10−4 S cm−1 at 70 °C. Cycling performance of these semi-interpenetrated SPE’s have been shown with a Li metal polymer battery and all solid -state Li sulphur battery.

Lithium-Sulfur (Li-S) battery technology is one of the promising candidates for next generation energy storage systems. Many studies have focused on the cathode materials to improve the cell performance. In this work we present a series of poly (S-DVB) copolymers synthesised by inverse vulcanization of sulfur with divinylbenzene (DVB). The poly (S-DVB) cathode shows excellent cycling performances at C/2 and C/4 current rates, respectively. It was demonstrated poly (S-DVB) copolymer containing 20% DVB did not influence the electrochemical performance of the sulfur material, compared to elemental sulfur as high specific capacities over ∼700 mAh g −1 at 500 cycles were achieved at C/4 current rate, comparable to conventional carbon-based S cathodes. However, the use of copolymer network is assumed to act firstly as sulfur reservoir and secondly as mechanical stabilizer, enhancing significantly the cycling lifetime. The Li-poly (S-DVB) cell demonstrated an extremely low degradation rate of 0.04% per cycle achieving over 1600 cycles at C/2 current rate.

Partial lithium substitution with nickel (0.25 of Ni2+ ion) in the previously reported Li1.5Fe0.5Ti1.5(PO4)3/C (LFTP@C) was performed to improve its structural and electrochemical properties. The new LiNi0.25Fe0.5Ti1.5(PO4)3/C (LNFTP@C) material was then tested as electrode for lithium ion batteries. In the voltage window 1.85V–3.0 V vs. Li+/Li, attractive electrochemical performances were obtained, mostly in terms of rate capability performance. At a current rate of 0.1C (6.6 mAg−1), the material delivered a capacity of around 120 mAhg−1, while at 5C, we observed a slight drop of the specific capacity reaching a value of 108 mAhg−1. Long-term cycling performance stability was also tested demonstrating a remarkable capacity decrease during the last 500 cycles. The capacity retention decreased from 94% to 91% after 500 cycles to about 77% and 74% after 1000 cycles at fast current rates of 5C (329.8 mAg−1) and 10C (659.6 mAg−1), respectively. In the wider voltage window, an average specific capacity of around 380 mAhg−1 was attained at a slow current rate of 0.1C.

Solid polymer electrolytes (SPEs) with new functionalized ethyl cellulose bearing a lithium/sodium fluorosulfonylimide group (Ethyl cellulose-LiFSI/NaFSI) is proposed as quasi single ion (Li+/Na+) conducting polymer electrolyte for all-solid-state lithium and sodium batteries. The degree of ethyl cellulose functionalization by anion of lithium and sodium salt measured by elemental analysis was 48 and 53%, respectively. The complex of Li(FSI-ethyl cellulose)/PEO exhibits a Li-ion transference number of TLi+ = 0.9, and a Na ion transference number of TNa+ = 0.6 for Na(FSI-ethyl cellulose),which are much higher than those reported for ambipolar LiFSI or NaFSI/PEO SPEs under the same measurement conditions. The generated SPEs showed a high electrochemical and mechanical stability as well as a practical ionic conductivity value of ~10−4 S·cm−1 at 80 °C. All solid-state lithium, sodium and Li/Sulfur cells cycled with quasi single ion conducting hybrid SPE exhibit reversible cycling and good performance at 70 °C, making them promising, environmentally benign and cost-effective candidates for use in advanced energy storage systems.

Green energy harvesting (solar and wind) and storage along with electrification of transport sector could bring about a major transformation in the CO2 emission levels that we are currently experiencing. Lithium ion batteries provide an efficient energy storage system to realize this goal. The key developments in Li-ion battery technology starting from solid solution electrodes, intercalation electrodes, conversion electrodes, organic electrodes, and polymer electrolytes with a major focus on the contribution of Michel Armand, an eminent scientist who at a young age saw the future of energy storage, have been elaborated. Moreover, the direction of research that seems interesting to pursue for realizing our goals has also been outlined.

The influence of temperature and moisture activity on the viscoelastic behavior of fluorinated membranes for fuel cell applications was investigated. Uncrosslinked and crosslinked ethylene tetrafluoroethylene (ETFE)-based proton-conducting membranes were prepared by radiation grafting and subsequent sulfonation and their behavior was compared with ETFE base film and commercial Nafion (R) NR212 membrane. Uniaxial tensile tests and stress relaxation tests at controlled temperature and relative humidity (RH) were carried out at 30 and 50 degrees C for 10%60%, with an almost single relaxation time exponential. An exponential decrease of relaxation time with RH from 60 s to 10 s was obtained at RH70% and 30 degrees C. The general behavior of grafted films observed at 30 degrees C was also obtained at 50 degrees C. However, an anomalous result was noticed for the membranes, with a higher modulus at 50 degrees C when compared with 30 degrees C. This behavior was explained by solvation of the sulfonic acid groups by water absorption creating hydrogen bonding within the clusters. A viscoelastic phase diagram was elaborated to map critical conditions (temperature and RH) for transitions in time-dependent behavior, from power-law scaling to exponential scaling. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1139-1148

Two new cathode materials based on redox organosulfur polymers were synthesized and investigated for rechargeable lithium batteries as a proof-of-concept study. These cathodes offered good cycling performance owing to the absence of polysulfide solubility, which plagues Li/S systems. Herein, an aliphatic polyamine or a conjugated polyazomethine was used as the base to tether the redox-active species. The activity comes from the cleavage and formation of S−S or N−S bonds, which is made possible by the rigid conjugated backbone. The synthesized polymers were characterized through FTIR spectroscopy and thermogravimetric analysis (TGA). Galvanostatic measurements were performed to evaluate the discharge/charge cycles and characterize the performance of the lithium-based cells, which displayed initial discharge capacities of approximately 300 mA h g−1 at C/5 over 100 cycles with approximately 98 % Coulombic efficiency.

We report on correlations between the proton conductivity, the water swelling and the dry-state morphology of ETFE-g-poly(sulfonated styrene-co-DVB) proton-exchange membranes (PEMs). We focus on the influence of the systematically varied monomer composition. Especially, the impact of the DVB cross-linker on the ion-rich phase aggregated in the dry PEM is studied by small-angle X-ray scattering. A modified hard-sphere fluid model describing the ion-rich phase is applied to interpret the observed scattering function. We find hereby that the size and number density of the ion-rich domains decrease with increasing cross-link level. Consequently, the distance between the ion-rich domains is proportional to the cross-link level. The total volume fraction of water in the hydrated membrane is proportional to the overall volume fraction of the ion-rich phase, and the number of water molecules per ion-rich aggregate is inversely proportional to the level of cross-linking. We show that there is a clear correlation between the structure of the ion-rich phase formed in the dry state and the proton conductivity of the hydrated membrane: beyond a threshold, indicating the onset of percolation of the aqueous network, the conductivity is proportional to the hydration level and inversely proportional to the mean distance between the ion-rich domains.

The relationships between the nano-scale structure and the monomer composition of proton exchange membranes (PEMs) are reported. The PEMs are synthesized by preirradiation-induced grafting ETFE with styrene and cross-linker, 1,3-diisopropenylbenzene (DIPB), where the styrene moieties are sulfonated subsequently. The degree of grafting is constant, while the DIPB level is varied systematically. The SAXS spectra of the dry membranes are isotropic and dominated by a single correlation peak, which results from the phase separation of the ion-rich phase from the polymer matrix. By analyzing the correlation peak we find that the number density and the typical size of the ion-rich domains decrease when the level of cross-linking is increased. The proton conductivity in the fully hydrated state is proportional to the volume fraction of the ion-rich phase. This suggests that the structure of the ion-rich phase found in the dry state has fundamental impact on the conductivity of the hydrated membrane. The relationship between the proton conductivity and the water volume fraction follows a power law in good agreement with percolation theory.

Styrene radiation grafted ETFE based proton conducting membranes are subject to degradation under fuel cell operating conditions and show a poor stability. Lifetimes exceeding 250 h can only be achieved with crosslinked membranes. In this study, a novel approach based on the increase of the intrinsic oxidative stability of uncrosslinked membranes is reported. Hence, the co-grafting of styrene with methacrylonitrile (MAN), which possesses a protected α-position and strong dipolar pendant nitrile group, onto 25 μm ETFE base film was investigated. Styrene/MAN co-grafted membranes were compared to a styrene based membrane in durability tests in single H2/O2 fuel cells. It is shown that the incorporation of MAN considerably improves the chemical stability, yielding fuel cell lifetimes exceeding 1000 h. The membrane preparation based on the co-grafting of styrene and MAN offers the prospect of tuning the MAN content and introduction of a crosslinker to enhance the oxidative stability of the resulting fuel cell membranes. Keywords: Polymer electrolyte fuel cell, Proton exchange membrane, Radiation grafting, Styrene, Methacrylonitrile, Membrane electrode assembly

Selective exposures of poly(ethylene-alt-tetrafluoroethylene) (ETFE) films with hard X-rays through high aspect ratio Ni-masks were performed at the LIGA3 beamline of the “Angstrom Quelle Karlsruhe” (ANKA) to create patterns of radicals used as initiators for the grafting of styrene into the bulk of the ETFE films. Grafted films were then sulfonated to obtain proton-conducting membranes. The structure definition, as investigated by scanning electron microscopy (SEM), showed a perfect discrimination between exposed and shaded areas through all the film thickness. Structuring results in a more homogeneous appearance of the membrane without affecting the degree of grafting and proton conductivity in the grafted areas. In fuel cell tests the structured membranes showed slightly lower performance due to 10% lower active area, but had a significantly higher lifetime.

Proton-exchange membranes are required to exhibit chemical, mechanical, and thermal stability for fuel cell applications. The present investigation has been carried out to explore the thermal behavior of poly(ethyl- ene-alt-tetrafluoroethylene) (ETFE)-based proton-conduct- ing membranes, both uncrosslinked and crosslinked, pre- pared by radiation grafting and subsequent sulfonation. The influence of preparation steps (irradiation, grafting, sulfonation, crosslinking) on the thermal degradation, crystallinity, and melting behavior of membranes with varying degree of grafting was examined. ETFE base film and grafted films were studied as the reference materials. Furthermore, poly(tetrafluoroethylene-co-hexafluoropro- pylene)-based grafted films and membranes were investi- gated as well for comparison. Membrane preparation steps, degree of grafting, crosslinking, type of base poly- mer have considerable inf luence on the thermal pro- perties of membranes. The crystallinity of the films decreases slightly by grafting, while a significant decrease was observed after sulfonation. For instance, crystallinity decreased from 37% (pristine ETFE) to 36% (uncrosslinked grafted film) and 23% (uncrosslinked ETFE-based membrane). On the other hand, the melting temperature of the base polymer was almost unaffected by irradiation and grafting. The crosslinked ETFE-based membranes exhibit a slightly higher melting temperature (262.58C) than their corresponding grafted films (261.38C) and the base film (260.68C). 2008 Wiley Periodicals, Inc. J Appl Polym Sci 108: 3577-3585, 2008

Crosslinking of styrene grafted and sulfonated fuel cell membranes is essential to obtaining well-performing and durable membranes. The properties and fuel cell performance of radiation grafted membranes based on ETFE (25 micron) with different extent of crosslinking, using divinylbenzene (DVB) as co-monomer to styrene, was investigated. At high degrees of crosslinking, fuel cell performance was limited by the high ohmic resistance of the membrane, whereas at low degrees of crosslinking the membrane-electrode interface was of poor quality. Optimum performance was obtained at a degree of crosslinking corresponding to a styrene:DVB monomer ratio (v/v) in the grafting solution of 95:5.

Crosslinked proton-exchange membranes were prepared by radiation-induced grafting of styrene into poly(ethylene- alt -tetrafluoroethylene) (ETFE) and subsequent sulfonation. The influence of the crosslinker, divinylbenzene (DVB), on various film and membrane properties was investigated in detail. A series of grafted films and membranes were prepared at varying DVB concentrations at a fixed graft level (∼25%) for this purpose. Grafting kinetics and kinetic parameters, including initial polymerization rate ( r po ), radical recombination rate ( γ ) and delay time ( t 0 ) at different DVB concentrations were evaluated. Moreover, resultant grafted films and membranes have been characterized with respect to their dimensional stability, chemical composition, thermal stability, crystallinity and fuel cell relevant properties. The concentration of crosslinker in the initial grafting solution was found to influence crucially the grafting reaction and graft levels. Dimensional increase, considerable especially after sulfonation, can be controlled by the introduction of DVB. Furthermore, the FTIR-ATR measurements exhibited that the grafted films were highly crosslinked within the surface near as compared to the entire bulk region. The influence of DVB on the crystallinity and thermal stability was not significant. On the contrary, the water uptake and proton conductivity of the membranes decreased substantially, while the IEC decreased slightly with increasing DVB concentration.

In this study, the effect of cross-linker content on the chemical stability of polyethylene-alt-tetrafluoroethyleneETFE-based radiation-grafted and sulfonated membranes was investigated. An ex situ degradation test in H2O2 solution showed a strong increase in stability of cross-linked membranes compared to uncross-linked ones. Excessive cross-linking, however, is detrimental to the chemical and mechanical properties. Furthermore, the stability of grafted membranes based on ETFE was superior to those based on polytetrafluoroethylene-co-hexafluoropropyleneFEP. An in situ long-term test in a H2/O2 single cell over 2180 h, using an ETFE-based grafted membrane optimized with respect to cross-linker content, with a graft level of 25% was carried out. The performance of the membrane electrode assembly exhibited a voltage decay rate of 13 Vh 1 over the testing time at a current density of 500 mA cm 2 and a cell temperature of 80°C, while the hydrogen permeation showed a steady increase over time. This indicates that, to some extent, changes in the membrane morphology occur over the operating period. Local postmortem analysis of the tested membrane reveals that high degradation was observed in areas adjacent to the O2 inlet and in other areas nearby.

Cross-linking of styrene grafted and sulfonated fuel cell membranes is essential to obtain well-performing and durable membranes. In this study, the properties and fuel cell performance of radiation grafted membranes based on poly(ethylene-alt-hexafluoropropylene) (ETFE) (25 μm) with different extent of cross-linking, using divinylbenzene (DVB) as a comonomer to styrene, were investigated. The water uptake and proton conductivity decrease as a function of increasing the extent of cross-linking. Also, the membranes become more brittle. Fuel cell performance is limited by the high ohmic resistance of the membrane at high degrees of cross-linking, whereas at low degrees of cross-linking the membrane-electrode interface is of poor quality. Optimum performance is obtained at an extent of cross-linking corresponding to a styrene:DVB monomer ratio (v/v) of 95:5 in the grafting solution.

A small-angle neutron scattering (SANS) investigation of saturated aqueous proton exchange membranes is presented. Our membranes were synthesized by radiation-induced grafting of poly(ethylene-alt-tetrafluoroethylene) (ETFE) with styrene in the presence of crosslinker (divinylbenzene, DVB) and the polystyrene was sulfonated subsequently. The contrast variation method was used to understand the relationship between morphology, water uptake, and proton conductivity. We find that the membranes are separated into two phases, mostly following the morphology already defined in the semi-crystalline ETFE base film. The amorphous phase hosts the water and swells upon hydration, swelling being inversely proportional to the degree of crosslinking. Proton conductivity and volumetric fraction of water are related by a power law, indicating a percolated and most likely random network of finely dispersed aqueous pores in the hydrophilic domains.