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ABSTRACT The first use of PS n- b-PEOm- b-PS n block copolymers (PS = polystyrene, PEO = poly(ethylene oxide)) as solid hosts for iodine/iodide electrolytes in dye-sensitized solar cells (DSSCs) is described. Using the benchmark photosensitizer N719, DSSC based on the quasi solid-state electrolytes afforded efficiencies up to 6.7%, to be compared with an efficiency of 7.3% obtained in similar conditions with a conventional iodine/iodide liquid electrolyte. By varying the PS:PEO relative volume ratio in the block copolymers different properties and morphologies were obtained. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 719-727 [ABSTRACT FROM AUTHOR]

The investigation of dye-sensitized solar cells (DSCs) using a very thin (0.8 to 4.7 μm) transparent photoanode based on a hierarchically nanostructured TiO2 film prepared via Plasma Assisted Supersonic Jet Deposition (PA-SJD), in combination with the DSC benchmark photosensitizer N719, is presented. The cell photovoltages (nearly 0.8 V) and the amount of adsorbed dye and photocurrent densities, normalized over the film thickness, are higher than those of DSCs prepared with thicker (9 μm) conventional screen-printed TiO2 films. A record efficiency value of 5.7% (standard AM 1.5G solar irradiation) for very thin nanostructured titania photoanodes is obtained with a 2 μm PA-SJD TiO2 film. Electrochemical impedance spectroscopy shows that PA-SJD devices are endowed with higher charge recombination resistance (lower recombination losses) and electron lifetimes compared to conventional nanocrystalline films. [ABSTRACT FROM AUTHOR]

Abstract: Na0.44MnO2 (NMO) is one of the most promising positive electrode materials for the development of sodium ion secondary batteries. In this work, a NMO orthorhombic compound was prepared by a soft chemistry modified Pechini method and characterized. The material exhibits a good discharge capacity (about 110mAh/g) at low current rate (11mA/g, C/25) which decreases to 65mAh/g at high rate (275mA/g, 1C). The electrochemical behavior was investigated by the extensive use of electrochemical impedance spectroscopy analysis. It was observed that the kinetic limitations are mainly due to the low diffusion coefficient of Na+ ions in the structure (in the range 10−13/10−14 cm2/s) and to the high values of the surface resistance which is the sum of two contributes attributed to the charge transfer process and the presence of a passivating layer. The diffusion coefficient as well as the charge transfer resistance depends on the sodium amount in the electrode. [Copyright &y& Elsevier]

A new heteroarylene-vinylene donor-acceptor low bandgap polymer, the poly(DEHT-V-BTD), containing vinylene-spaced efficient donor (dialkoxythiophene) and acceptor (benzothiadiazole) moieties, is presented. Electropolymerization has been carried out by several electrochemical techniques and the results are compared. In particular, the pulsed potentiostatic method was able to provide layers with sufficient amounts of material. Cyclic voltammetries showed reversible behavior towards both p- and n-doping. The HOMO, LUMO, and bandgap energies were estimated to be -5.3, -3.6 and 1.8 eV, respectively. In situ UV-Vis measurements have established that the presence of the vinylene group stabilizes the formation of polaronic charge carriers even at high doping levels. [ABSTRACT FROM AUTHOR]

A facile and fast approach, based on microwave-enhanced Sonogashira coupling, has been employed to obtain in good yields both mono- and, for the first time, disubstituted push-pull ZnII porphyrinates bearing a variety of ethynylphenyl moieties at the β-pyrrolic position(s). Furthermore, a comparative experimental, electrochemical, and theoretical investigation has been carried out on these β-mono- or disubstituted ZnII porphyrinates and meso-disubstituted push-pull ZnII porphyrinates. We have obtained evidence that, although the HOMO-LUMO energy gap of the meso-substituted push-pull dyes is lower, so that charge transfer along the push-pull system therein is easier, the β-mono- or disubstituted push-pull porphyrinic dyes show comparable or better efficiencies when acting as sensitizers in DSSCs. This behavior is apparently not attributable to more intense B and Q bands, but rather to more facile charge injection. This is suggested by the DFT electron distribution in a model of a β-monosubstituted porphyrinic dye interacting with a TiO2 surface and by the positive effect of the β substitution on the incident photon-to-current conversion efficiency (IPCE) spectra, which show a significant intensity over a broad wavelength range (350-650 nm). In contrast, meso-substitution produces IPCE spectra with two less intense and well-separated peaks. The positive effect exerted by a cyanoacrylic acid group attached to the ethynylphenyl substituent has been analyzed by a photophysical and theoretical approach. This provided supporting evidence of a contribution from charge-transfer transitions to both the B and Q bands, thus producing, through conjugation, excited electrons close to the carboxylic anchoring group. Finally, the straightforward and effective synthetic procedures developed, as well as the efficiencies observed by photoelectrochemical measurements, make the described β-monosubstituted ZnII porphyrinates extremely promising sensitizers for use in DSSCs. [ABSTRACT FROM AUTHOR]

A new heteroarylene-vinylene donor-acceptor polymer P(BDT-V-BTD) with reduced bandgap has been synthesized and its photophysical, electronic and photovoltaic properties investigated both experimentally and theoretically. The structure of the polymer comprises an unprecedented combination of a strong donor (4,8-dialkoxy-benzo[1,2- b:4,5- b']dithiophene, BDT), a strong acceptor (2,1,3-benzothiadiazole, BTD) and a vinylene spacer. The new polymer was obtained by a metal-catalyzed cross-coupling Stille reaction and fully characterized by NMR, UV-vis absorption, GPC, TGA, DSC and electrochemistry. Detailed ab initio computations with solvation effects have been performed for the monomer and model oligomers. The electrochemical investigation has ascertained the ambipolar character of the polymer and energetic values of HOMO, LUMO and bandgap matching materials-design rules for optimized organic photovoltaic devices. The HOMO and LUMO energies are consistently lower than those of previous heteroarylene-vinylene polymer while the introduction of the vinylene spacer afforded lower bandgaps compared to the analogous system P(BDT-BTD) with no spacer between the aromatic rings. These superior properties should allow for enhanced photovoltages and photocurrents in photovoltaic devices in combination with PCBM. Preliminary photovoltaic investigation afforded relatively modest power conversion efficiencies of 0.74% (AM 1.5G, 100 mW/cm2), albeit higher than that of previous heteroarylene-vinylene polymers and comparable to that of P(BDT-BTD). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 [ABSTRACT FROM AUTHOR]

Mesoporous Cr or Pt-doped WO thin films to be employed as ammonia gas sensors were prepared by a fast one-step sol-gel procedure, based on the use of triblock copolymer as templating agent. The obtained films were constituted by aggregates of interconnected WO nanocrystals (20-50 nm) separated by mesopores with dimensions ranging between 2 and 15 nm. The doping metals, Pt and Cr, resulted differently hosted in the WO mesoporous matrix. Chromium is homogeneously dispersed in the oxide matrix, mainly as Cr(III) and Cr(V) centers, as revealed by EPR spectroscopy; instead platinum segregated as Pt (0) nanoparticles (4 nm) mainly included inside the WO nanocrystals. The semiconductor layers containing Pt nanoclusters revealed, upon exposure to NH, remarkable electrical responses, much higher than Cr-doped and undoped layers, particularly at low ammonia concentration (6.2 ppm). This behavior was attributed to the presence of Pt nanoparticles segregated inside the semiconductor matrix, which act as catalysts of the N-H bond cleavage, decreasing the activation barrier in the ammonia dissociation. The role of the mesoporous structure in influencing the chemisorption and the gas diffusion in the WO matrix appeared less decisive than the electronic differences between the two examined doping metals. The overall results suggest that a careful combination between mesoporous architecture and metal doping can really promote the electrical response of WO toward ammonia. [ABSTRACT FROM AUTHOR]

Abstract: The development of lithium ion aqueous batteries is getting renewed interest due to their safety and low cost. We have demonstrated that the layer-structure LiCoO2 phase, the most commonly used electrode material in organic systems, can be successful delithiated and lithiated again in a water-based electrolyte at currents up to 2.70A/g. The capacity is about 100mAh/g at 0.135A/g and can be tuned by cycling the electrode in different potential ranges. In fact, increasing the high cut-off voltage leads to higher specific capacity (up to 135mAh/g) but the Coulomb efficiency is reduced (from 99.9% to 98.5%). The very good electrode kinetic is probably due to the high conductivity of the electrolyte solution (0.17Scm−1 at 25°C) but this behavior is affected by the electrode load. [Copyright &y& Elsevier]

Abstract: Silicon nanowires (SiNWs) have the potential to perform as anodes for lithium-ion batteries with a much higher energy density than graphite. However, there has been little work in understanding the surface chemistry of the solid electrolyte interphase (SEI) formed on silicon due to the reduction of the electrolyte. Given that a good, passivating SEI layer plays such a crucial role in graphite anodes, we have characterized the surface composition and morphology of the SEI formed on the SiNWs using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). We have found that the SEI is composed of reduction products similar to that found on graphite electrodes, with Li2CO3 as an important component. Combined with electrochemical impedance spectroscopy, the results were used to determine the optimal cycling parameters for good cycling. The role of the native SiO2 as well as the effect of the surface area of the SiNWs on reactivity with the electrolyte were also addressed. [Copyright &y& Elsevier]

Abstract: The structural transformations of silicon nanowires when cycled against lithium were evaluated using electrochemical potential spectroscopy and galvanostatic cycling. During the charge, the nanowires alloy with lithium to form an amorphous Li x Si compound. At potentials <50mV, a structural transformation occurs. In studies on micron-sized particles previously reported in the literature, this transformation is a crystallization to a metastable Li15Si4 phase. X-ray diffraction measurements on the Si nanowires, however, show that they are amorphous, suggesting that a different amorphous phase (Li y Si) is formed. Lithium is removed from this phase in the discharge to form amorphous silicon. We have found that limiting the voltage in the charge to 70mV results in improved efficiency and cyclability compared to charging to 10mV. This improvement is due to the suppression of the transformation at low potentials, which alloys for reversible cycling of amorphous silicon nanowires. [Copyright &y& Elsevier]

The use of Sr-Mg-doped LaGaO3 (LSGM), a highly conducting oxygen ion electrolyte, in intermediate temperature solid oxide fuel cells (IT-SOFC) technology requires suitable electrode materials. Because the Sr-doped LaMnO3 (LSM) cathode coupled with the YSZ electrolyte had shown relatively good performances, it has been also suggested for LSGM-based cells. As cathode overpotential is the main performance limitation, the optimization of the LSM/LSGM interface might be of fundamental relevance in the technology development of LSGM-based IT-SOFC. LSM films with different porosities were screen printed on both faces of the LSGM pellets; their morphology and electrical properties were investigated by scanning electron microscopy and impedance spectroscopy, respectively. Porosity was induced by the addition of icing sugar (3–5 wt%) to the LSM powder during ink preparation. Homogeneous electrode layers with a thickness of about 30 μm were obtained. The higher the sugar amount, the higher the film porosity and the lower the LSM grain size. The Nyquist plots show two low frequency arcs to which the charge transfer and mass transfer process or oxygen dissociation process were associated, respectively. One can expect that the best electrochemical performances are obtained using highly porous electrode. [ABSTRACT FROM AUTHOR]

Abstract: The redox process mechanism responsible for the colour change in poly(3,4-ethylene-dioxythiophene) (PEDOT) was investigated in order to understand the nature and the role of the chemical species involved. PEDOT layers were obtained by chemical polymerisation with iron (III) p-toluenesulphonate. The films were then cycled several times in LiClO4/propylene carbonate (PC) electrolyte. The chemical composition of ‘as-prepared’ and cycled films (in the reduced and oxidised state) was studied by means of EDX and XPS ex situ analysis. The results point out the fundamental role the electrolyte anion plays in the process and provide quantitative information about the extent of anion exchange. [Copyright &y& Elsevier]

We present relevant results dealing with the transparency/optical nonlinearity trade-off in high-frequency electro-optic applications. The very simple, stable and high optical gap chromophore, the zwitterion 1-methyl-4-(tetrazol-5-ate)pyridinium, represents the best transparency/optical nonlinearity trade-off so far described in the literature. We rationalize this remarkable performance in the framework of the Bond Length Alternation theory by means of a multidisciplinary approach including: single crystal X-ray structure, Electric Field Induced Second-Harmonic Generation, solvatochromism, electrochemistry and thermal analyses. [ABSTRACT FROM AUTHOR]

Abstract: Despite the large number of studies on the behavior of LiCoO2 in organic electrolytes and its recent application as a positive electrode in rechargeable water battery prototypes, a little information is available about the lithium intercalation reaction in this layered compound in aqueous electrolytes. This work shows that LiCoO2 electrodes can be reversibly cycled in LiNO3 aqueous electrolytes for tens of cycles at remarkably high rates with impressive values specific capacity higher than 100mAh/g, and with a coulomb efficiency greater than 99.7%. Stable and reproducible cycling measurements have been made using a simple cell design that can be easily applied to the study of other intercalation materials, assuming that they are stable in water and that their intercalation potential range matches the electrochemical stability window of the aqueous electrolyte. The experimental arrangement uses a three-electrode flooded cell in which another insertion compound acts as a reversible source and sink of lithium ions, i.e., as the counter electrode. A commercial reference electrode is also present. Both the working and the counter electrodes have been prepared as thin layers on a metallic substrate using the procedures typical for the study of electrodes for lithium-ion batteries in organic solvent electrolytes. [Copyright &y& Elsevier]

The effect of the type of dopant (titanium and manganese) and of the reduced graphene oxide content (rGO, 30 or 50 wt %) of the α-Fe2O3@rGO nanocomposites on their microstructural properties and electrochemical performance was investigated. Nanostructured composites were synthesized by a simple one-step solvothermal method and evaluated as anode materials for sodium ion batteries. The doping does not influence the crystalline phase and morphology of the iron oxide nanoparticles, but remarkably increases stability and Coulombic efficiency with respect to the anode based on the composite α-Fe2O3@rGO. For fixed rGO content, Ti-doping improves the rate capability at lower rates, whereas Mn-doping enhances the electrode stability at higher rates, retaining a specific capacity of 56 mAhg−1 at a rate of 2C. Nanocomposites with higher rGO content exhibit better electrochemical performance. [ABSTRACT FROM AUTHOR]

Invited for this month's cover are the collaborating groups of Prof. Luca Beverina from the University of Molani‐Bicocca, Italy and Prof. Michael Sommer from Chemnitz University of Technology, Germany. The front cover shows the thermally induced transformation of a soluble and electron‐rich naphthalene tetraester–bithiophene copolymer into the corresponding insoluble and electron‐poor naphthalenetetraanhydride derivative. The combination of monochromatic squares, inspired by the work of Josef Albers, shows the color change involved in the transformation. Read the full text of the article at 10.1002/cplu.201900210. [ABSTRACT FROM AUTHOR]

Keywords: materials science; polymerization; semiconductors; thermochemistry; voltammetry B The front cover b shows the thermally induced transformation of a soluble and electron-rich naphthalenetetraester-bithiophene copolymer into the corresponding insoluble and electron-poor naphthalenetetraanhydride derivative. Materials science, polymerization, semiconductors, thermochemistry, voltammetry. [Extracted from the article]