Synthesis and Properties of Poly(ether sulfone)s with Clustered Sulfonic Groups for PEMFC Applications under Various Relative Humidity

Novel sulfonated poly­(ether sulfone) copolymers (S4PH-<i>x</i>-PSs) based on a new aromatic diol containing four phenyl substituents at the 2, 2′, 6, and 6′ positions of 4,4′-diphenyl ether were synthesized. Sulfonation was found to occur exclusively on the 4 position of phenyl substituents by NMR spectroscopy. The ion exchange capacity (IEC) values can be controlled by adjusting the mole percent (<i>x</i> in S4PH-<i>x</i>-PS) of the new diol. The fully hydrated sulfonated poly­(ether sulfone) copolymers had good proton conductivity in the range 0.004–0.110 S/cm at room temperature. The surface morphology of S4PH-<i>x</i>-PSs and Nafion 212 was investigated by atomic force microscopy (tapping-mode) and related to the percolation limit and proton conductivity. Single H₂/O₂ fuel cell based on S4PH-40-PS loaded with 0.25 mg/cm² catalyst (Pt/C) exhibited a peak power density of 462.6 mW/cm², which was close to that of Nafion 212 (533.5 mW/cm²) at 80 °C with 80% RH. Furthermore, fuel cell performance of S4PH-35-PS with various relative humidity was investigated. It was confirmed from polarization curves that the fuel cell performance of S4PH-35-PS was not as high as that of Nafion 212 under fully hydrated state due to higher interfacial resistance between S4PH-35-PS and electrodes. While under low relative humidity (53% RH) at 80 °C, fuel cells based on S4PH-35-PS showed higher peak power density (234.9 mW/cm²) than that (214.0 mW/cm²) of Nafion 212

Design for Approaching Cicada-Wing Reflectance in Low- and High-Index Biomimetic Nanostructures

Natural nanostructures in low refractive index Cicada wings demonstrate ≤1% reflectance over the visible spectrum. We provide design parameters for Cicada-wing-inspired nanotip arrays as efficient light harvesters over a 300–1000 nm spectrum and up to 60° angle of incidence in both low-index, such as silica and indium tin oxide, and high-index, such as silicon and germanium, photovoltaic materials. Biomimicry of the Cicada wing design, demonstrating gradient index, onto these material surfaces, either by real electron cyclotron resonance microwave plasma processing or by modeling, was carried out to achieve a target reflectance of ∼1%. Design parameters of spacing/wavelength and length/spacing fitted into a finite difference time domain model could simulate the experimental reflectance values observed in real silicon and germanium or in model silica and indium tin oxide nanotip arrays. A theoretical mapping of the length/spacing and spacing/wavelength space over varied refractive index materials predicts that lengths of ∼1.5 μm and spacings of ∼200 nm in high-index and lengths of ∼200–600 nm and spacings of ∼100–400 nm in low-index materials would exhibit ≤1% target reflectance and ∼99% optical absorption over the entire UV–vis region and angle of incidence up to 60°

Electronic Supplementary Materials including models and fitting of the electrochemical impedance spectroscopy, XRD, XPS, EDX spectra, and polarization curves. from Enhanced hydrogen evolution reaction on hybrids of cobalt phosphide and molybdenum phosphide

Production of hydrogen from water electrolysis has stimulated the search of sustainable electrocatalysts as possible alternatives. Recently, cobalt phosphide (CoP) and molybdenum phosphide (MoP) received great attention due to their superior catalytic activity and stability towards the hydrogen evolution reaction (HER) which rivals platinum catalysts. In this study, we synthesize and study a series of catalysts based on hybrids of CoP and MoP with different Co/Mo ratio. The HER activity shows a volcano shape and reaches a maximum for Co/Mo = 1. Tafel analysis indicates a change in the dominating step of Volmer–Hyrovský mechanism. Interestingly, X-ray diffraction patterns confirmed a major ternary interstitial hexagonal CoMoP₂ crystal phase is formed which enhances the electrochemical activity

Functionalizing Biomaterials to Be an Efficient Proton-Exchange Membrane and Methanol Barrier for DMFCs

Biobased materials capable of transforming into selective proton-exchange composite membranes (PEMs) are highly favored for use in direct methanol fuel cells (DMFCs) because of their low cost and abundance. Here, a polysaccharide and a clay have been functionalized together to make a highly proton selective PEM. Use of chitosan and clay composites ensured limited methanol crossover and thereby high measured performance via efficient fuel convertibility. In this study, sulfonated natural nanocomposite PEMs made of chitosan and sodium–montmorillonite (CS-MMT) were characterized for their water swelling, proton conductivity and methanol permeability parameters. The CS-MMT membrane with a proton conductivity of 4.92 × 10^–2 S cm^–1 and a power density of 45 mW/cm² showed a measured methanol crossover current density (<i>J</i>) of <100 mA/cm². For higher methanol concentrations (4, 6 and 8 M), fuel loss was ∼4 times less in comparison with commercially successful PEMs, such as Nafion 117

Thickness-Dependent Binding Energy Shift in Few-Layer MoS₂ Grown by Chemical Vapor Deposition

The thickness-dependent surface states of MoS₂ thin films grown by the chemical vapor deposition process on the SiO₂–Si substrates are investigated by X-ray photoelectron spectroscopy. Raman and high-resolution transmission electron microscopy suggest the thicknesses of MoS₂ films to be ranging from 3 to 10 layers. Both the core levels and valence band edges of MoS₂ shift downward ∼0.2 eV as the film thickness increases, which can be ascribed to the Fermi level variations resulting from the surface states and bulk defects. Grainy features observed from the atomic force microscopy topographies, and sulfur-vacancy-induced defect states illustrated at the valence band spectra imply the generation of surface states that causes the downward band bending at the n-type MoS₂ surface. Bulk defects in thick MoS₂ may also influence the Fermi level oppositely compared to the surface states. When Au contacts with our MoS₂ thin films, the Fermi level downshifts and the binding energy reduces due to the hole-doping characteristics of Au and easy charge transfer from the surface defect sites of MoS₂. The shift of the onset potentials in hydrogen evolution reaction and the evolution of charge-transfer resistances extracted from the impedance measurement also indicate the Fermi level varies with MoS₂ film thickness. The tunable Fermi level and the high chemical stability make our MoS₂ a potential catalyst. The observed thickness-dependent properties can also be applied to other transition-metal dichalcogenides (TMDs), and facilitates the development in the low-dimensional electronic devices and catalysts

PALM Output.

<p>The result page consists of five parts. A). Job parameters. The job ID and user-defined parameters in the submission are included. B). Tree topology drawn by <i>PalmTree</i>, an interactive topology viewer with displaying options of bootstrapping value and branch length. A mouse click on a branching point can make the sub-tree flip; a click on the end node (round, with sequence ID) removes the sequence from the submitted data set before reinitiating an analysis procedure. C). Information about the best model selected by <i>PalmDaemon</i>. D). Statistics on all models calculated by <i>PalmDaemon</i>. E). Download area for those files generated from the entire PALM process.</p

Transparent, Broadband, Flexible, and Bifacial-Operable Photodetectors Containing a Large-Area Graphene–Gold Oxide Heterojunction

In this study, we combine graphene with gold oxide (AuO_<i>x</i>), a transparent and high-work-function electrode material, to achieve a high-efficient, low-bias, large-area, flexible, transparent, broadband, and bifacial-operable photodetector. The photodetector operates through hot electrons being generated in the graphene and charge separation occurring at the AuO_<i>x</i>–graphene heterojunction. The large-area graphene covering the AuO_<i>x</i> electrode efficiently prevented reduction of its surface; it also acted as a square-centimeter-scale active area for light harvesting and photodetection. Our graphene/AuO_<i>x</i> photodetector displays high responsivity under low-intensity light illumination, demonstrating picowatt sensitivity in the ultraviolet regime and nanowatt sensitivity in the infrared regime for optical telecommunication. In addition, this photodetector not only exhibited broadband (from UV to IR) high responsivity3300 A W^–1 at 310 nm (UV), 58 A W^–1 at 500 nm (visible), and 9 A W^–1 at 1550 nm (IR)but also required only a low applied bias (0.1 V). The hot-carrier-assisted photoresponse was excellent, especially in the short-wavelength regime. In addition, the graphene/AuO_<i>x</i> photodetector exhibited great flexibility and stability. Moreover, such vertical heterojunction-based graphene/AuO_<i>x</i> photodetectors should be compatible with other transparent optoelectronic devices, suggesting applications in flexible and wearable optoelectronic technologies

Pyrolysis of Iron–Vitamin B9 As a Potential Nonprecious Metal Electrocatalyst for Oxygen Reduction Reaction

This study presents the performance of a carbon-black-supported pyrolyzed vitamin B9 (folic acid)-treated cathode catalyst (py-Fe-FA/C) in the oxygen reduction reaction (ORR) and proton exchange membrane fuel cell (PEMFC). Electrochemical ORR measurements revealed that using py-Fe-FA/C resulted in excellent ORR activity through the direct four-electron reduction pathway. The H₂–O₂ PEMFC with py-Fe-FA/C in the cathodic side produces a maximum power density of 330 mW cm^–2 with the 80 °C operation temperature and the 1 atm back pressure. X-ray photoelectron spectroscopy and <i>in situ</i> X-ray adsorption spectroscopy proved that the enhanced ORR activity was caused by the network structure of polyaromatic hydrocarbons, quaternary-type (graphitic) nitrogen, and the coordination structure of the py-Fe-FA/C, as confirmed by the ORR mechanism study using detailed XPS and <i>in situ</i> X-ray adsorption spectroscopy. Particularly, <i>in situ</i> X-ray adsorption spectroscopy elucidated the ORR mechanism of the py-Fe-FA/C

Infrastructure and workflow of PALM.

<p>Infrastructure and workflow of PALM.</p

Side Group of Poly(3-alkylthiophene)s Controlled Dispersion of Single-Walled Carbon Nanotubes for Transparent Conducting Film

Controlled dispersion of single-walled carbon nanotubes (SWCNTs) in common solvents is a challenging issue, especially for the rising need of low cost flexible transparent conducting films (TCFs). Utilizing conductive polymer as surfactant to facilitate SWCNTs solubility is the most successful pragmatic approach to such problem. Here, we show that dispersion of SWCNT with polymer significantly relies on the length of polymer side groups, which not only influences the diameter distribution of SWCNTs in solution, also eventually affects their effective TCF performance. Surfactants with longer side groups covering larger nanotube surface area could induce adequate steric effect to stabilize the wrapped SWCNTs against the nonspecific aggregation, as discerned by the optical and microscopic measurements, also evidenced from the resultant higher electrokinetic potential. This approach demonstrates a facile route to fabricate large-area SWCNTs-TCFs exhibiting high transmittance and high conductivity, with considerable uniformity over 10 cm × 10 cm