Cathode catalyst layer using supported Pt catalyst on ordered mesoporous carbon for direct methanol fuel cell

The development of a cathode catalyst layer based on a supported Pt catalyst using an ordered mesoporous carbon (OMC) for direct methanol fuel cell is reported. An OMC with a mesopore structure between hexagonally arranged carbon nanorods is prepared using a template method. Platinum nanoparticles are supported on the OMC (Pt/OMC) with high metal loading of 60 wt.%. Compositional and morphological variations are made by varying the ionomer content and by compressing the catalyst layer to detect a parameter that determines the power performance. Increase in power density with decrease in the volume fraction of ionomer in the agglomerate comprising the Pt/OMC and the ionomer indicates that mass transport through the ionomer phase governs the kinetics of oxygen reduction. Impedance spectroscopic analysis suggests that a significant mass-transport limitation occurs at high ionomer content and in the compressed cathode. The power density of the optimum cathode layer, which employs a Pt/OMC catalyst with a Pt loading of 2 mg cm⁻², is greater than that of a catalyst layer with 6 mg cm⁻² Pt-black catalyst at a voltage higher than 0.4 V. This would lead to a significant reduction in the cost of the membrane electrode assembly.     

A new synthetic procedure for ordered mesoporous γ-alumina using phthalic acid as an interfacial protector

Employing phthalic acid (PA) as an interfacial protector and P123 as a structure-directing agent, ordered mesoporous γ-alumina with 2D hexagonal symmetry was successfully synthesized through the sol-gel method. According to the results, the best molar ratio of PA/Al³⁺ to synthesize the ordered alumina is 0.25 and the phthalic acid serves as an interfacial protector to protect the aluminum ions at the organic-inorganic interface from being affected by chloride ions during the whole evaporation process. The resulting alumina possesses a surface area of 431.98 m²/g and a pore volume of 0.42 cm³/g. After the alumina converted into the γ-alumina phase, the surface area is still 226.37 m²/g and has a pore volume of 0.31 cm³/g.     

High rate capability of ordered mesoporous carbon with platelet graphitic pore walls for lithium ion anodes

An ordered mesoporous carbon (OMC) with controllable molecule crystal and platelet graphitic pore walls, which is directionally grown on the internal pore walls of SBA-15 or anchors at liquid/silica interfaces by molecule engineering, has been investigated as lithium ion anodes. It is found that the OMC exhibits high kinetics, rate and cycling performance. The i₀ and D_Li are almost constant after 50 cycles. OMC shows a high reversible specific capacity of 153.9 mAh g^-1 at the current density as high as 3500 mA g^-1. The excellent electrochemical performance could be attributed to the presence of the porosity and platelet graphitic pore walls.     

Templated synthesis of ordered porous TiO2 films and their application in dye-sensitized solar cell

Ordered porous TiO₂ thin films were fabricated on conductive glass by using colloid crystal template of polystyrene (PS) spheres. Microstructural characterization by scanning electron microscopy techniques was carried out to explore the porous structural changes due to the PS templates which could be controlled by adjusting the drawing rate. Photovoltaic performance was measured and this revealed the effect of microstructural changes. The results showed that monolayer porous TiO₂ films and multilayer porous TiO₂ films could be successfully prepared. And multilayer porous TiO₂ films provided large surface area for dye absorption to increase the efficiency of dye-sensitized solar cells (DSSCs) which were assembled by porous TiO₂ films.     

Thin films of Cu(In,Ga)Se2 and ordered vacancy compound prepared by thermal crystallization and their photovoltaic applications

Thin films of Cu–In–Ga–Se alloy system with various composition were prepared by thermal crystallization from In/CuInGaSe/In precursor. Electron probe microanalysis and X-ray diffraction study revealed that these samples were assigned to chalcopyrite Cu(In,Ga)Se₂ or ordered vacancy compound Cu(In,Ga)₂Se_3.5. Solar cell with ZnO:Al/i–ZnO/CdS/Cu(In,Ga)Se₂/Mo/soda-lime glass substrate structure was fabricated by using thermal crystallization technique, and demonstrated a 9.58% efficiency without AR-coating.     

Gender differences in injury severity risks in crashes at signalized intersections

This paper analyzes gender differences in crash risk severities using data for signalized intersections. It estimates gender models for injury severity risks and finds that driver condition, type of crash, type of vehicle driven and vehicle safety features have different effects on females’ and males’ injury severity risks. Also, it finds some variables which are significantly related to females’ injury severity risks but not males’ and others which affect males’ injury severity risks but not females’. It concludes that better and more in-depth information about gender differences in injury severity risks is gained by estimating separate models for females and males.     

Characterization of stepwise flash evaporated CuIn3Se5 films

CuIn₃Se₅ thin films were grown by stepwise flash evaporation from the polycrystalline powder source. Bulk CuIn₃Se₅ was synthesized by melt-quench technique, starting from the stoichiometric mixture of constituent elements. Phase purity of the synthesized material was confirmed by powder X-ray diffraction. Structural investigations by transmission electron microscopy (TEM) show that the films grown at 370 K and above were polycrystalline in nature. Compositional analysis by Rutherford backscattering spectrometry (RBS) revealed that the films have near stoichiometric composition. Analysis of optical transmittance data yielded a band gap value of 1.26±0.02 eV.     

Microstructure of Si Cones Prepared by Ar^＋—Sputtering Si／Mo Target

By Ar^ sputtering onto Si wafers which were surrounded by Mo plates.uniform cones over a large area on the Si surface were formed.Scanning electron microscopic study showed that the cones were formed on the entire surface of the Si wafer.The dimensions of the uniform cones were one micrometer in diameter and 5-6 micrometers high.They were further characterized by means of cross-sectional transmission electron microscopy,with the technique of micro-diffractions,It was found that the cone contained a pure Si regime and a Mo-rich regime.In the binary Mo-Si zone,we identified three distinct areas vertically:(1)domains of Mo-induced Si ordered structures,(2)a small volume of a new Mo3Si2 structural variant,intergrown with the Si ordered structure,and(3) a small amount of pure Mo nanoparticles covering the surface of the cones.The formation of the large and uniform cones may provide a new surface configuration for potential applications in surface science and technology.     

Performance analysis of the ordered and the conventional catalyst layers in proton exchange membrane fuel cells

Two steady-state, one-dimensional models of the cathode active layer for the proton exchange membrane fuel cell, a conventional active layer model with the agglomerate structure and an ordered active layer model, have been compared. The model equations account for the Tafel kinetics of oxygen reduction reaction, proton migration and oxygen diffusion in the polymer electrolyte and gas pores. The polarization curves simulated by the ordered active layer predict a superior performance than the conventional active layer model even with lower platinum loadings. Analysis of the overpotential contributions indicates that the better performance of the ordered catalyst layer can be attributed to the reduction of concentration polarization. Simulation results also reveal that the ordered active layer gives more uniform oxygen concentration and overpotential distributions while the conventional catalyst layer shows more evenly distributed local current source. The present results will be helpful for practical fuel cell designs.     

Highly Ordered Self‐Assembled Architectures of Modified Terpyridines on Highly Ordered Pyrolitic Graphite Imaged by Scanning Tunneling Microscopy

Scanning tunneling microscopy has been used to study the adsorbed phases of functionalized terpyridines at the solid–liquid interface of highly ordered pyrolitic graphite (HOPG). Terpyridines are well‐known for their complexing behavior to transition metal ions, making them widely used ligands in organometallic and supramolecular chemistry. We found that solutions of 2,2′:6′,2″‐terpyridine‐4′‐oxydodecane (tpy‐O‐C12) and 2,2′:6′,2″‐4′‐oxyoctadecane (tpy‐O‐C18) form highly ordered two‐ dimensional (2D) arrays on HOPG in phenyloctane. For both compounds, large, well‐defined lamellar domains have been observed with domain sizes larger than 500 nm. Sequential scans of an area with two grain boundaries indicate that desorption–resorption is taking place along the domain edges. High‐resolution images of the lamella have been obtained, and the 2D packing within the lamella was determined in detail. The terpyridines align in long uniform double rows with their alkyl chains packing in an alternating, zipper‐like fashion. The terpyridines pack with the polar head‐groups head to head, and the observed size and shape of the molecules fit exactly to their modeled geometries.