Phosphorylated chitosan/poly(vinyl alcohol) based proton exchange membranes modified with propylammonium nitrate ionic liquid and silica filler for fuel cell applications

In our previous work, phosphorylated chitosan was modified through polymer blending with poly(vinyl alcohol) (PVA) polymer to produce N-methylene phosphonic chitosan/poly(vinyl alcohol) (NMPC/PVA) composite membranes. The aim of this work is to further investigate the effects of a propylammonium nitrate (PAN) ionic liquid and/or silicon dioxide (SiO₂) filler on the morphology and physical properties of NMPC/PVA composite membranes. The temperature-dependent ionic conductivity of the composite membranes with various ionic liquid and filler compositions was studied by varying the loading of PAN ionic liquid and SiO₂-PAN filler in the range of 5–20 wt%. As the loading of PAN ionic liquid increased in the NMPC/PVA membrane matrix, the ionic conductivity value also increased with the highest value of 0.53 × 10^?3 S cm^?1 at 25 °C and increased to 1.54 × 10^?3 S cm^?1 at 100 °C with 20 wt% PAN. The NMPC/PVA-PAN (20 wt%) composite membrane also exhibited the highest water uptake and ion exchange capacity, with values of 60.5% and 0.60 mequiv g^?1, respectively. In addition, in the single-cell performance test, the NMPC/PVA-PAN (20 wt%) composite membrane displayed a maximum power density, which was increased by approximately 14% compared to the NMPC/PVA composite membrane with 5 wt% SiO₂-PAN. This work demonstrated that modified NMPC/PVA composite membranes with ionic liquid PAN and/or SiO₂ filler showed enhanced performance compared with unmodified NMPC/PVA composite membranes for proton exchange membrane fuel cells.     

Pt–Ru nanoparticles anchored on poly(brilliant cresyl blue) as a new polymeric support: Application as an efficient electrocatalyst in methanol oxidation reaction

The glassy carbon electrode is modified by poly(brilliant cresyl blue) (PBCB) to be applied as a new green and efficient platform for Pt and Pt–Ru alloy nanoparticles deposition. Surface composition, morphology and catalytic activity of these modified electrodes towards methanol oxidation are assessed by applying X-ray diffraction, field emission scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy techniques. The X-ray diffraction patterns reveal that the highly crystalline Pt and Pt–Ru alloy and RuO₂ nanoparticles with low crystallinity are deposited on the PBCB modified glassy carbon electrodes. The microscopic images indicate smaller size and better distribution of deposited nanoparticles on the surface of PBCB modified electrodes. Cyclic voltammetry and electrochemical impedance spectroscopy results reveal that PBCB supported Pt and Pt–Ru nanoparticles have better electrocatalytic performance and durability towards methanol oxidation rather than the unsupported nanoparticles. From the obtained results it can be concluded that the presence of PBCB not only improves the stability of nanoparticles on the surface, but also leads to the formation of smaller size and more uniform distribution of nanoparticles on the surface, which, in turn, cause the nanoparticles to provide a higher accessible surface area and more active centers for the oxidation of methanol. The results will be valuable in extending the applications of this polymer in surface modification steps and in developing promising catalyst supports to be applied in direct methanol fuel cells.     

Synthesis of Cellulose-Based Macromolecular Coupling Agent and its Utilization in Poly (butylene succinate)/Wood Flour Composites

A long fatty side chain was introduced into the macromolecule of hydroxyethyl cellulose (HEC) via esterification reaction. The hydrophobicity of hydroxyethyl cellulose lauric acid ester (HECLAE) was enhanced in comparison with HEC. The obtained HECLAE was used as macromolecular coupling agent in poly (butylene succinate)/wood flour composites and exhibited a positive influence on improving the mechanical performance of composites. Besides, HECLAE plays a role as a hydrophobic agent in composites. A significant increase in storage modulus (E’) was observed upon the incorporation of treated wood flour. SEM images showed that the dispersion of treated wood flour in PBS matrix was improved.     

Nickel foam-supported Fe,Ni-Polyporphyrin microparticles: Efficient bifunctional catalysts for overall water splitting in alkaline media

Developing highly active, stable and sustainable electrocatalysts for overall water splitting is of great importance to generate renewable H₂ for fuel cells. Herein, we report the synthesis of electrocatalytically active, nickel foam-supported, spherical core-shell Fe-poly(tetraphenylporphyrin)/Ni-poly(tetraphenylporphyrin) microparticles (FeTPP@NiTPP/NF). We also show that FeTPP@NiTPP/NF exhibits efficient bifunctional electrocatalytic properties toward both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). Electrochemical tests in KOH solution (1 M) reveal that FeTPP@NiTPP/NF electrocatalyzes the OER with 100 mA cm⁻² at an overpotential of 302 mV and the HER with 10 mA cm⁻² at an overpotential of 170 mV. Notably also, its catalytic performance for OER is better than that of RuO₂, the benchmark OER catalyst. Although its catalytic activity for HER is slightly lower than that of Pt/C (the benchmark HER electrocatalyst), it shows greater stability than the latter during the reaction. The material also exhibits electrocatalytic activity for overall water splitting reaction at a current density of 10 mA cm⁻² with a cell voltage of 1.58 V, along with a good recovery property. Additionally, the work demonstrates a new synthetic strategy to an efficient, noble metal-free-coordinated covalent organic framework (COF)-based, bifunctional electrocatalyst for water splitting.     

Annealing and doping-dependent magnetoresistance in single layer poly(3-hexyl-thiophene) organic semiconductor device

We compare the current density–voltage (J–V) and magnetoconductance (MC) response of a poly(3-hexyl-thiophene) (P3HT) device (Au/P3HT(350 nm)/Al) before and after annealing above the glass transition temperature of 150 °C under vacuum. There is a decrease of more than 3 orders of magnitude in current density due to an increase of the charge injection barriers after de-doping through annealing. An increase, approaching 1 order of magnitude, in the negative MC response after annealing can be explained by a shift in the Fermi level due to de-doping, according to the bipolaron mechanism. We successfully tune the charge injection barrier through re-doping by photo-oxidation. This leads to the charge injection and transport transitioning from unipolar to ambipolar, as the bias increases, and we model the MC response using a combination of bipolaron and triplet-polaron interaction mechanisms.     

A new polymer electrolyte poly(acrylonitrile)-dimethylsulphoxide-salt for electrochemical capacitors

The PAN-DMSO-Et₄NBF₄ and PAN-DMSO-Et₄NTf (Tf is triflate ion) electrolytes were prepared as white, turbid foils with a thickness in the range of 0.1-0.5 mm, using the casting technique. Room temperature conductance of the electrolytes, detected from ac impedance experiments, was at the level of 8 and 14 mS cm⁻¹ for Et₄NBF₄ and Et₄NTf salts, respectively. The electrochemical stability window of approximately 2.6-2.8 V was estimated using a glassy carbon electrode. Temperature dependence of the conductivity is of the Arrhenius-type for both electrolytes, with an activation energy of approximately 34 kJ mol⁻¹. The double-layer capacitors built with these electrolytes, serving both as separators and activated carbon powder (ACP) binders, showed a specific capacity of 50 F g⁻¹ of carbon material. Capacitors were assembled by sandwiching the PAN-DMSO-salt electrolyte between two PAN-salt-DMSO-ACP-AB electrodes and pressing across the system; the resulting devices had a coin-like shape with 8 mm diameter and thickness between 2.0 and 2.5 mm.     

Staining of poly(ethylene terephthalate) by ruthenium tetroxide

The staining of poly(ethylene terephthalate) (PET) by ruthenium tetroxide (RuO₄) is used to obtain a contrast at the crystalline lamellar scale in transmission electron microscopy. This paper demonstrates the efficiency of this technique conducted in vapor phase on ultracut bulk samples. Advantages of this method against other contrast enhancing techniques and the parameters of staining are discussed. The depth of attack is measured and is shown to be limited by a crosslinking process. The chemical mechanisms are investigated by grazing infrared spectroscopy and involve the oxidation of the aliphatic moeities of PET.     

Photoelectrochemistry of poly(3-methylthiophene), I: Surface morphology and thickness effect

Photocyclovoltammetric experiments with films of poly(3-methylthiophene) under polychromatic light irradiation show a p-type semiconductor behavior in the reduced state, with a flat band potential of 0.18 V. The photocurrent depends on film thickness and surface morphology. Films with different thickness were characterized by scanning electron microscopy, indicating a globular morphology with globule sizes changing according to the charge density used during polymer deposition. The highest photocurrent is observed for the lowest globule diameter. These films were also irradiated with monochromatic light from the electrolyte side and from the substrate side. A higher photocurrent and a photocurrent spectrum matching the absorption spectrum of the reduced form of the polymer is observed on irradiation from the electrolyte side of a 0.7 μm thick film. In contrast, for irradiation from the electrode side, the photocurrent is lower and the spectrum shows a peak at lower energy. These results were interpreted in terms of a delocalized space charge zone, different kinetics for charge transfer and mass transport across the solvent swollen polymer film and different depth of penetration of the light as a function of wavelength.     

A facile and efficient method for preparation of chiral supported poly(styrene–divinylbenzene) copolymers

A new and efficient method for preparation of optically active poly(styrene–divinylbenzene) copolymers (PS-DVB) is presented here. This is carried out by Friedel–Crafts acylation reaction of chiral N-phthaloyl -leucine acid chloride with PS-DVB beads in the presence of aluminum chloride as Lewis acid catalyst and 1,2-dichloroethane as the solvent at ambient temperature. Reagents’ amounts and reaction conditions are mentioned and four samples with different amounts of functionality have been prepared. Final products were characterized by FT-IR and elemental analysis. The results obtained confirm that the above modification in preparation of chiral supported PS-DVB has been achieved well and in moderate yield.     

Synthesis and characterization of a series of star-branched poly(ε-caprolactone)s with the variation in arm numbers and lengths

A series of star-branched poly(ε-caprolactone)s (SPCLs) was synthesized with structural variation of the arm numbers and lengths through ring-opening polymerization under bulk condition. Arm numbers were varied to be 3, 4, and 6 by using multifunctional initiating cores such as trimethylol propane, pentaerythritol, and dipentaerythritol, respectively. The lengths of the poly(ε-caprolactone) arms were varied by controlling the molar ratio of monomer-to-initiating hydroxyl group molar ratio ([CL]₀/[-OH]₀=5, 10, 15). Molecular weights were determined by both ¹H NMR end-group analysis and MALDI-TOF mass spectrometry, which gave reasonably consistent values. On the contrary, the GPC method failed to give accurate values of molecular weight of SPCLs due to the discrepancy with the linear standard. The branching architecture of SPCLs was evaluated by the branching ratio, g, which is the ratio of the mean-square radius of SPCL to that of liner counterpart, linear poly(ε-caprolactone) (LPCL), which is of the same chemistry and having the same molecular weight. The radii of gyration of SPCLs and LPCLs were determined using small-angle X-ray scattering (SAXS) from the initial slopes of Zimm plots, represented as 1/I(q) vs q² with I(q) and q being the scattered intensity and scattering vector, respectively. The g values were observed to decrease with increasing arm numbers, indicating more compact molecular structure for SPCLs with higher arm numbers, while no such effect was observed for arm length variation. Thermal properties as well as the degree of crystallinity of SPCLs were found to be also dependent on structural variations. The melting points and the degradation temperatures were observed to increase with increasing arm lengths but with constant arm number. On the other hand, arm number variation with constant arm length gave no such changes to the thermal transitions of SPCLs. However, for the SPCLs with equivalent molecular weights, the degree of crystallinity was found to decrease with increasing arm numbers.