Search

We have investigated the effects of localized surface plasmons (LSPs) on the performance of quasi-solid-state dye-sensitized solar cells (DSSCs). Ag and Au nanoparticles (NPs) were prepared by photoreduction in the presence of generation 5 polyester hydroxyl acetylene bis(hydroxymethyl)propanoic acid dendrons (Dendron) as a stabilizer. The plasmon-enhanced DSSCs were achieved by incorporating metal@Dendron NPs into TiO photoanodes. The presence of dendrons prevents the photoelectrons from recombining on the surface of TiO semiconductor and improves the stability of metal NPs. With the addition of Ag@Dendron NPs, the photocurrent and the power conversion efficiency of quasi-solid-state DSSCs increased due to the LSP effect of metal NPs and the barrier effect of dendron, which were confirmed by the increased incident photon-to-photocurrent efficiency and by electrochemical impedance spectroscopy analysis. [ABSTRACT FROM AUTHOR]

This study examined the effect of palladium (Pd) ions on the performance and stability of silver-polymer complex membranes composed of AgBF and poly( N-vinyl pyrrolidone) (PVP) for the separation of propylene/propane mixtures. The separation performances including the selectivity of propylene/propane and mixed gas permeance through the PVP/AgBF membrane decreased continuously due mainly to the reduction of silver ions to silver nano-particles. On the other hand, upon the addition of Pd ions, enhanced membrane stability along with the higher separation performance was achieved. This demonstrates that Pd ions play a role in preventing the reduction of silver ions and participating directly in the facilitated propylene transport. UV analysis of the membranes shows that the rate of silver nano-particle formation was retarded significantly by the addition of Pd salts. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Solution casting films of sulfonated poly[styrene- b-(ethylene- r-butylene)- b-styrene] copolymer (sSEBS)-based composite membranes that contained different amounts of organic, nanorod-shaped polyrotaxane were annealed at various temperatures for 1 h. The films' properties were characterized with respect to their use as polymer electrolyte membranes in direct methanol fuel cells (DMFCs). Different aspect ratios of polyrotaxane were prepared using the inclusion-complex reaction between α-cyclodextrin and poly(ethylene glycol). The presence of the organic polyrotaxane inside the membrane changed the morphology during the membrane preparation and reduced the transport of methanol. The conductivity and methanol permeability of the composite membranes decreased with increasing polyrotaxane content, while the annealing temperature increased. All of the sSEBS-based, polyrotaxane composite membranes annealed at 140 °C showed a higher selectivity parameter, suggesting their potential usage for DMFCs. [ABSTRACT FROM AUTHOR]

Cast DNA/polyethyleneimine (PEI) blend membranes containing different amounts of DNA were prepared using acid-base interaction and characterized with the aim of understanding the polymer electrolyte membrane properties. Two different molecular weights of PEI were used to provide the mechanical strength, while DNA, a polyelectrolyte, was used for the proton transport channel. Proton conductivity was observed for the DNA/PEI membrane and reached approximately 3.0 × 10 S/cm for a DNA loading of 16 wt% at 80 °C. The proton transport phenomena of the DNA/PEI complexes were investigated in terms of the complexation energy using the density functional theory method. In the case of DNA/PEI, a cisoid-type complex was more favorable for both the formation of the complex and the dissociation of hydrogen from the phosphate. Since the main requirement for proton transport in the polymer matrix is to dissociate the hydrogen from its ionic sites, this suggests the significant role played by the basicity of the matrix. [ABSTRACT FROM AUTHOR]

Polymer electrolyte membranes, featuring ionic channels, were prepared from sulfonated dextran/ poly(vinyl alcohol) (sD/PVA) membranes. A stiff sulfated dextran was chosen as the route for ionic transport, since ionic sites are located along the stiff dextran main chain. The sD/PVA blend membranes were annealed and then chemically crosslinked. The characteristics of the crosslinked sD/PVA membranes were investigated to determine their suitability as proton exchange membranes. The proton conductivity was found to increase with increasing amounts of sD inside the membrane, which reached a maximum and then decreased when the sD content exceeded 30 wt%, while the methanol permeability increased with increasing sD content. The good dispersion of sD inside the membrane, which serves as an ionic channels mimic, played a significant role in proton transportation. [ABSTRACT FROM AUTHOR]

Novel composite membranes, which delivered high separation performance for propylene/propane mixtures, were developed by coating inert poly(ethylene- co-propylene) rubber (EPR) onto a porous polyester substrate, followed by the physical distribution of AgBF. Scanning electron microscopy-wavelength dispersive spectrometer (SEM-WDS) revealed that silver salts were uniformly distributed in the EPR layer. The physical dispersion of the silver salts in the inert polymer matrix, without specific interaction, was characterized by FT-IR and FT-Raman spectroscopy. The high separation performance was presumed to stem from the in-situ dissolution of crystalline silver ionic aggregates into free silver ions, which acted as an active propylene carrier within a propylene environment, leading to facilitated propylene transport through the membranes. The membranes were functional at all silver loading levels, exhibiting an unusually low threshold carrier concentration (less than 0.06 of silver weight fraction). The separation properties of these membranes, i.e. the mixed gas selectivity of propylene/propane ~55 and mixed gas permeance ~7 GPU, were stable for several days. [ABSTRACT FROM AUTHOR]

In this paper, we describe a prospective approach to increasing the metal ionic conductivity of solid polymer electrolytes by using the anion complexation between the anion of the metal salt and the solvent matrix. We have prepared a new type of solid polymer electrolyte (CP/LiCl/ PVC) and demonstrated its excellent ionic conductivity. The high ionic conductivity of this material is attributed to anion complexation between the anions and their receptors (CPs) dissolved in the PVC matrix. The anion complexation of CP, which should help to increase both the concentration of free Li and its mobility, is more favorable with Cl than ClO . Consequently, such systems have high cation conductivity and characteristics of high performance electrolytes that are required to achieve high power density and good rechargeability for lithium batteries. [ABSTRACT FROM AUTHOR]

Ionic cluster mimic, polymer electrolyte membranes were prepared using polymer composites of crosslinked poly(vinyl alcohol) (PVA) with sulfated-β-cyclodextrins (β-CDSOH) or phosphated-β-cyclodextrins (β-CDPO(OH)). When Nafion, developed for a fuel cell using low temperature, polymer electrolyte membranes, is used in a direct methanol fuel cell, it has a methanol crossover problem. The ionic inverted micellar structure formed by micro-segregation in Nafion, known as ionic cluster, is distorted in methanol aqueous solution, resulting in the significant transport of methanol through the membrane. While the ionic structure formed by the ionic sites in either β-CDSOH or β-CDPO(OH) in this composite membrane is maintained in methanol solution, it is expected to reduce methanol transport. Proton conductivity was found to increase in PVA membranes upon addition of ionized cyclodextrins. Methanol permeability through the PVA composite membrane containing cyclodextrins was lower than that of Nafion. It is thus concluded that the structure and fixation of ionic clusters are significant barriers to methanol crossover in direct methanol fuel cells. [ABSTRACT FROM AUTHOR]

Remarkably high and stable separation performance for olefin/paraffin mixtures was previously reported by facilitated olefin transport through π-complex membranes consisting of silver ions dissolved in poly(hexamethylenevinylene) (PHMV). In this study, the π-complex formation of AgBF, AgClO and AgCFSO with PHMV and their ionic interactions were investigated. FT-Raman spectroscopy showed that the C=C stretching bands of PHMV shifted to a lower frequency upon incorporation of silver salt, but the degree of peak shift depended on the counteranions of salt due to different complexation strengths. The symmetric stretching modes of anions indicated the presence of only free ions up to [C=C]∶[Ag]=1∶1, demonstrating the unusually high solubility of silver salt in PHMV. Above the solubility limit, the ion pairs and higher-order ionic aggregates started to form. The coordination number of silver ion for C=C of PHMV was in the order AgBF>AgClO>AgCFSO, but became similar at [C=C]∶[Ag]=1∶1. The different coordination number was interpreted in terms of the different transient crosslinks of silver cations in the complex, which may be related to both the interaction strength of the polymer/silver ion and the bulkiness of the counteranion. [ABSTRACT FROM AUTHOR]

Cast Nafion-based composite membranes containing different amounts of organic, nanorod-shaped polyrotaxane were prepared and characterized, with the aim of improving the properties of polymer electrolyte membranes for direct methanol fuel cell applications. Polyrotaxane was prepared using the inclusion-complex reaction between α-cyclodextrin and poly(ethylene glycol) (PEG) of different molecular weights. The addition of polyrotaxane to Nafion changed the morphology and reduced the crystallinity. The conductivity of the composite membranes increased with increasing polyrotaxane content up to 5 wt%, but then decreased at higher polyrotaxane contents. Well-dispersed, organic polyrotaxane inside the membrane can provide a tortuous path for the transport of methanol, as the methanol permeability depends on the aspect ratio of polyrotaxane, which is controlled by the molecular weight of PEG. All of the Nafion-based, polyrotaxane composite membranes showed a higher selectivity parameter than the commercial Nafion films did. [ABSTRACT FROM AUTHOR]

The transport of reactant gas, electrons and protons at the three phase interfaces in the catalytic layers of membrane electrode assemblies (MEAs) in proton exchange, membrane fuel cells (PEMFCs) must be optimized to provide efficient transport to and from the electrochemical reactions in the solid polymer electrolyte. The aim of reducing proton transport loss in the catalytic layer by increasing the volume of the conducting medium can be achieved by filling the voids in the layer with small-sized electrolytes, such as dendrimers. Generation 1.5 and 3.5 polyamidoamine (PAMAM) dendrimer electrolytes are well-controlled, nanometer-sized materials with many peripheral ionic exchange, -COOH groups and were used for this purpose in this study. The electrochemically active surface area of the deposited catalyst material was also investigated using cyclic voltammetry, and by analyzing the Pt-H oxidation peak. The performances of the fuel cells with added PAMAM dendrimers were found to be comparable to that of a fuel cell using MEA, although the Pt utilization was reduced by the adsorption of the dendrimers to the catalytic layer. [ABSTRACT FROM AUTHOR]

Cellulose nitrate (CN) composite membranes, containing cobalt porphyrin (CoP) complexes self-assembled within nanometer-sized rhenium clusters (ReCoP), have been prepared and their oxygen and nitrogen gas permeabilities were analyzed. The solubility of ReCoP and the characteristics of the corresponding composite membranes were analyzed using a Cahn microbalance, FT-IR spectroscopy, wide-angle X-ray scattering, and differential scanning calorimetry. The nitrogen permeability through the CN composite membranes decreased upon addition of ReCoP and CoP, which implies that the presence of these oxygen carrier complexes affects the structure of the polymer matrix. The oxygen permeability through the composite membranes containing small quantities of ReCoP decreased, but it increased upon increasing the concentration. The oxygen gas transport was affected by the matrix at low ReCoP concentrations, but higher concentrations of ReCoP increased the oxygen permeability as a result of its reversible and specific interactions with oxygen, effectively realizing ReCoP carrier-mediated oxygen transport. [ABSTRACT FROM AUTHOR]

Facilitated transport membranes for the separation of olefin/paraffin mixtures have long been of interest in separation membrane science because olefins, such as propylene and ethylene, which are important chemicals in petrochemical industries, are currently separated by energy-intensive cryogenic distillation processes. Recently, solid polymer electrolyte membranes containing silver ions have demonstrated remarkable performance in the separation of olefin/paraffin mixtures in the solid state and, thus, they can be considered as alternatives to cryogenic distillation. Here, we review recent progress, and critical issues affecting in the use of facilitated olefin transport membranes; in particular, we provide a general overview with reference to carrier properties, transport mechanisms, and separation performance. [ABSTRACT FROM AUTHOR]

Silver salt complex membranes with glassy poly(methyl methacrylate) (PMMA) unexpectedly showed higher propylene permeance than those with rubbery poly(butyl methacrylate) (PBMA) where as neat PMMA is much less permeable to propylene than that of neat PBMA. Such unusual facilitated olefin transport has been systematically investigated by changing the side chain length of polymethacrylates (PMAs) from methyl, ethyl to butyl. The ab initio calculation showed almost the same electron densities of the carbonyl oxygens in the three PMAs, expecting very similar intensity of the interaction between carbonyl oxygen and silver ion. However, the interaction intensity decreases with the length of the alkyl side chain: PMMA > PEMA > PBMA according to wide angle X-ray scattering and FT-Raman spectroscopy. The difference in the interaction intensity may arise from the difference in the hydrophilicity of the three PMAs, as confirmed by the contact angle of water, which determines the concentrations of the ionic constituents of silver salts: free ion, contact ion pair and higher order ionic aggregate. However, propylene solubilities and facilitated propylene transport vary with the side chain length significantly even at the same concentration of the free ion, the most active olefin carrier, suggesting possible difference in the prohibition of the molecular access of propylene to silver ion by the side chains: the steric hindrance. Therefore, it may be concluded that both the hydrophilicity and the steric hindrance associated with the side chain length in the three PMAs are of pivotal importance in determining facilitated olefin transport through polymer/silver salt complex membranes. [ABSTRACT FROM AUTHOR]

Silver species other than the silver ion were formed by UV irradiation on polymer electrolyte membranes containing silver salts and their effect on complexation behavior between the silver and olefin was investigated through the separation performance of olefin/paraffin mixtures. The ideal propylene/propane separation factor reached 350 and the separation coefficient was ca. 15 due to the high loading amount of silver ions into poly(2-ethyl-2-oxazoline) (POZ) without UV irradiation. On UV irradiation either in air or under nitrogen, the silver-POZ membranes became yellow-brown initially due to the formation of colloidal silver particles, and finally black and metal-like luster. Even when Ag was converted, to some extent, to Ag° by UV irradiation in air at the early stage, the separation coefficient of olefin/paraffin mixtures was maintained. This suggests that silver species other than the silver ion is active for olefin carrier for facilitated transport. Meanwhile the steady decrease of the separation coefficient was observed in the silver/POZ membranes irradiated under N. It is suggested that the reduction of silver ions in POZ goes through a different photoreduction mechanism with UV irradiation depending on the environment. [ABSTRACT FROM AUTHOR]