Nanometer‐Scale Water‐ and Proton‐Diffusion Heterogeneities across Water Channels in Polymer Electrolyte Membranes

Nafion, the most widely used polymer for electrolyte membranes (PEMs) in fuel cells, consists of a fluorocarbon backbone and acidic groups that, upon hydration, swell to form percolated channels through which water and ions diffuse. Although the effects of the channel structures and the acidic groups on water/ion transport have been studied before, the surface chemistry or the spatially heterogeneous diffusivity across water channels has never been shown to directly influence water/ion transport. By the use of molecular spin probes that are selectively partitioned into heterogeneous regions of the PEM and Overhauser dynamic nuclear polarization relaxometry, this study reveals that both water and proton diffusivity are significantly faster near the fluorocarbon and the acidic groups lining the water channels than within the water channels. The concept that surface chemistry at the (sub)nanometer scale dictates water and proton diffusivity invokes a new design principle for PEMs.     

Raman spectroscopy of alkali halide hydration: hydrogen bond relaxation and polarization

The solute–solvent interaction of salts has a striking impact on various biological and industrial processes but its mechanism remains yet mysterious despite intensive studies since 1888 when Franz Hofmeister established the salt series. A combination of confocal Raman spectroscopy and contact angle measurements has enabled us to resolve the hydrogen bond relaxation (O:H―O, HB) and the associated charge polarization dynamics at different molecular site because of alkali halides hydration. Results show consistently that salt hydration softens the O:H phonon but stiffens H―O phonon cooperatively. The extent of HB relaxation and polarization is proportional to the electronegativity difference and ionic radius, following the order of Hofmeister series: X (R/η) = I (2.2/2.5) > Br (1.96/2.8) > Cl (1.81/3.0) > F (1.33/4.0) ≈ 0 for anions, and Y(R/η) = Na (0.98/0.9) > K (1.33/0.8) > Rb (1.49/0.8) > Cs (1.65/0.8) for cations. Observations suggest that ions create each an electric field that aligns, stretches, and polarizes water molecules, which relaxes the O:H―O bond cooperatively, depresses the molecular dynamics, and enhances the hydration shell viscosity and the skin stress. Exercises also demonstrate that Raman spectroscopy performs as a powerful tool for probing the molecular‐site‐resolved HB network relaxation dynamics in terms of phonon stiffness, molecular fluctuation dynamics, and phonon abundance transition under external stimulus. Copyright © 2016 John Wiley & Sons, Ltd.     

Plasmonic nano‐slits assisted polarization selective detour phase meta‐hologram

Traditional detour‐phase hologram is a powerful optical device for manipulating phase and amplitude of light, but it is usually not sensitive to the polarization of light. By introducing the light‐metasurface interaction mechanism to the traditional detour phase hologram, we design a novel plasmonic nano‐slits assisted polarization selective detour phase meta‐hologram, which has attractive advantages of polarization multiplexing ability, broadband response, and ultra‐compact size. The meta‐hologram relies on the dislocations of plasmonic slits to achieve arbitrary phase distributions, showing strong polarization selectivity to incident light due to the plasmonic response of deep‐subwavelength slits. To verify its polarization sensitive and broadband responses, we experimentally demonstrate two holographic patterns of an optical vortex and an Airy beam at p‐ and s‐polarized light with wavelengths of 532nm, 633nm and 780nm, respectively. Furthermore, we realize an application example of the meta‐hologram as a polarization multiplexed photonic device for multi‐channel optical angular momentum (OAM) generation and detection. Such meta‐holograms could find widespread applications in photonics, such as chip‐level beam shaping and high‐capacity OAM communication.

     

Mechanical polishing,surface roughness,near‐surface deformation,and electrochemical corrosion of Alloy 690TT

The effects of mechanical grinding/polishing, surface roughness, and near‐surface deformation on the electrochemical corrosion behavior of thermally treated (TT) Alloy 690 were studied in a sodium chloride solution. The X‐ray photoelectron spectroscopy and transmission electron microscopy analyses revealed that mechanical grinding/polishing can change the ratio of the elements at the surface of the as‐received Alloy 690TT specimen by removing its Cr‐rich outer layer and causing deformation at the near‐surface microstructure, something which has a direct impact on the rate of the oxygen reduction reaction (ORR), the pitting potential (E_pit), and the corrosion potential (E_corr) of Alloy 690TT. It was observed that the ratio of Cr in the surface is a significant factor that controls the rate of the ORR and the corrosion parameters such as E_corr. Higher amounts of Cr at the surface accelerate the ORR. The near‐surface deformation shifts the E_pit values towards less positive potentials. It was also found that due to the different near‐surface chemical composition of the as‐received Alloy 690TT specimen compared with the ground and the polished specimens, the surface roughness parameters do not have a regular correlation with the rate of the ORR and the values of the E_corr and the E_pit. Only the passive current density increases when the surface roughness is increased. Copyright © 2015 John Wiley & Sons, Ltd.     

Tetrazolo[1,5‐a]quinoline‐4‐carbaldehyde and its Schiff base on mild steel as corrosion inhibitor in 1 M HCl solution: electrochemistry,theoretical and SEM surface analysis

The corrosion inhibition impact of two quinoline derivatives, viz tetrazolo [1,5‐a] quinoline‐4‐carbaldehyde ( TQC ) and (Z) ?5‐methyl‐N‐(tetrazolo [1,5‐a] quinolin‐4‐ylmethylene) thiazol‐2‐amine ( MTQT ), has been examined against mild steel in 1 M HCl solution using conventional weight loss, potentiodynamic polarization, linear polarization, electrochemical impedance spectroscopy, quantum chemical, and scanning electron microscopic studies. The experimental results have showed that TQC and MTQT revealed a good corrosion inhibition and that the inhibition efficiency increases with the increase of concentration of inhibitor to attain 94.54% for TQC and 99.25% for MTQT at 25 ppm. Polarization measurements suggest that TQC and MTQT act as a mixed‐type inhibitor. A synergism between inhibitors can be observed by polarization measurements. Electrochemical impedance spectroscopy measurements show an increase of the transfer resistance with the inhibitor concentration. Adsorption of TQC and MTQT on the mild steel surfaces in 1 N HCl solution follows the Langmuir adsorption isotherm model. Furthermore, quantum chemical calculations have been conducted using B3LYP functional and 6‐31G(d,p) basis set to complement the experimental evidences. Copyright © 2015 John Wiley & Sons, Ltd.     

Polarizable coarse‐grained models for molecular dynamics simulation of liquid cyclohexane

Force field parameters for polarizable coarse‐grained (CG) supra‐atomic models of liquid cyclohexane are proposed. Two different bead sizes were investigated, one representing two fine‐grained (FG) CH₂r united atoms of the cyclohexane ring, and one representing three FG CH₂r united atoms. Electronic polarizability is represented by a massless charge‐on‐spring particle connected to each CG bead. The model parameters were calibrated against the experimental density and heat of vaporization of liquid cyclohexane, and the free energy of cyclohexane hydration. Both models show good agreement with thermodynamic properties of cyclohexane, yet overestimate the self‐diffusion. The dielectric properties of the polarizable models agree very well with experiment. © 2015 Wiley Periodicals, Inc.     

Electrochemical characterization of MnO2 as electrocatalytic energy material for fuel cell electrode

 Development of inexpensive non Pt based high electrocatalytic energy materials is the need of the hour for fuel cell electrode to produce clean alternative green energy from synthesized bio alcohol using biomass. MnO₂, electro synthesized at different current density is found to be well performed electrocatalytic material, comparable to Pt, with higher current density, very low overvoltage for the electrochemical oxidation of methanol. From EIS study, the polarization resistance of the coated MnO₂ is found to be much low and electrical double layer capacitance is high, the effect increases with increase in current density of electro deposition. XRD, EDX and AAS analysis confirm the MnO₂ deposition. The morphology of SEM images exhibits an enhanced 3D effective substrate area, for electro oxidation of the fuel. A few nano structured grains of the deposited MnO₂ is also observed at higher current density. The fact supports that a high energetic inexpensive electro catalytic material has been found for fuel cell electrode to synthesis renewable energy from methanol fuel.     

Combining linear polarization spectroscopy and the Representative Layer Theory to measure the Beer–Lambert law absorbance of highly scattering materials

Visible and Near Infrared (Vis–NIR) Spectroscopy is a powerful non destructive analytical method used to analyze major compounds in bulk materials and products and requiring no sample preparation. It is widely used in routine analysis and also in-line in industries, in-vivo with biomedical applications or in-field for agricultural and environmental applications. However, highly scattering samples subvert Beer–Lambert law's linear relationship between spectral absorbance and the concentrations. Instead of spectral pre-processing, which is commonly used by Vis–NIR spectroscopists to mitigate the scattering effect, we put forward an optical method, based on Polarized Light Spectroscopy to improve the absorbance signal measurement on highly scattering samples. This method selects part of the signal which is less impacted by scattering. The resulted signal is combined in the Absorption/Remission function defined in Dahm's Representative Layer Theory to compute an absorbance signal fulfilling Beer–Lambert's law, i.e. being linearly related to concentration of the chemicals composing the sample. The underpinning theories have been experimentally evaluated on scattering samples in liquid form and in powdered form. The method produced more accurate spectra and the Pearson's coefficient assessing the linearity between the absorbance spectra and the concentration of the added dye improved from 0.94 to 0.99 for liquid samples and 0.84–0.97 for powdered samples.     

A circular dichroism sensor for Ni and Co based on l-cysteine capped cadmium sulfide quantum dots

A new circular dichroism sensor for detecting Ni²⁺ and Co²⁺ was proposed for the first time using chiral chelating quantum dots. The detection principle was based on changing of circular dichroism signals of the chiral quantum dots when forming a chiral complex with Ni²⁺ or Co²⁺. l-Cysteine capped cadmium sulfide quantum dots (l-Cyst-CdS QDs) were proposed as a chiral probe. The CD spectrum of l-Cyst-CdS QDs was significantly changed in the presence of Ni²⁺ and Co²⁺. On the other hand, other studied cations did not alter the original CD spectrum. Moreover, when increasing the concentration of Ni²⁺ or Co²⁺, the intensity of the CD spectrum linearly increased as a function of concentration and could be useful for the quantitative analysis. The proposed CD sensor showed linear working concentration ranges of 10–60 μM and 4–80 μM with low detection limits of 7.33 μМ and 1.13 μM for the detection of Ni²⁺ and Co²⁺, respectively. Parameters possibly affected the detection sensitivity such as solution pH and incubation time were studied and optimized. The proposed sensor was applied to detect Ni²⁺ and Co²⁺ in real water samples, and the results agreed well with the analysis using the standard ICP-OES.     

Structure and electronic properties of hollow‐caged C60 fullerene‐derived (MN4)nC6(10 − n) (M = Zn,Mg, Fe,n = 1−6) complexes

Unique hollow‐caged (MN₄)_nC_{6(10 ? n)} (M = Zn, Mg, Fe, n = 1?6) complexes designed by introduction of n porphyrinoid fragments in C₆₀ fullerene structure were proposed and the atomic and electronic structures were calculated using LC‐DFT MPWB95 and M06 potentials and 6‐311G(d)/6‐31G(d) basis sets. The complexes were optimized using various symmetric configurations from the highest O_h to the lowest C₁ point groups in different spin states from S = 0 (singlet) to S = 7 (quindectet) for M = Fe to define energetically preferable atomic and electronic structures. Several metastable complexes were determined and the key role of the metal ions in stabilization of the atomic structure of the complexes was revealed. For Fe₆N₂₄C₂₄, the minimum energy was reported for C_2h, D_2h, and D_4h symmetry of pentet state S = 2, so the complex can be regarded as unique molecular magnet. It was found that the metal partial density of states determine the nature of HOMO and LUMO levels making the clusters promising catalysts. © 2014 Wiley Periodicals, Inc.