ABSTRACT:We have designed and synthesized a polyaniline (PANI)-decorated Pt/C@PANI core−shell catalyst that shows enhanced catalyst activity and durability compared with nondecorated Pt/C. The experimental results demonstrate that the activity for the oxygen reduction reaction strongly depends on the thickness of the PANI shell and that the greatest enhancement in catalytic properties occurs at a thickness of 5 nm, followed by 2.5, 0, and 14 nm. Pt/C@PANI also demonstrates significantly improved stability compared with that of the unmodified Pt/C catalyst. The high activity and stability of the Pt/C@PANI catalyst is ascribed to its novel PANIdecorated core−shell structure, which induces both electron delocalization between the Pt d orbitals and the PANI π-conjugated ligand and electron transfer from Pt to PANI. The stable PANI shell also protects the carbon support from direct exposure to the corrosive environment. P roton exchange membrane fuel cells (PEMFCs) are regarded as ideal candidates for stationary and mobile power generation because of their high energy conversion efficiencies and low environmental impact.1 However, the insufficient electrocatalytic activity and durability of Pt cathode catalysts still remains a major obstacle for PEMFC applications.2 At present, the most commonly used cathode catalysts are highly dispersed 2−5 nm Pt nanoparticles (NPs) supported on carbon. However, Pt NPs suffer from poor durability because of the rapid and significant loss of platinum electrochemical surface area (ECSA) over time due to corrosion of the carbon support, Pt dissolution, Ostwald ripening, and aggregation. and optimization of the catalyst structure to increase the exposure of Pt NPs to the three-phase zone. 7 Although these methods have been proposed to enhance the catalytic activity and durability, the development of a Pt-based catalyst with both good durability and high mass activity remains a challenge.Conducting polymers such as polypyrrole (PPy) and polyaniline (PANI) have received special attention in fuel cell applications because of their unique π-conjugated structures, which lead to good environmental stability, high electrical and proton conductivity in acidic environments, and unique redox properties. 8 Recently, Deki and co-workers 9 reported the preparation of a Pt/electroconductive-polymer-loaded carbon composite that improved the durability of electrodes in fuel cells. In that study, Pt(NH 3 ) 4 2+ was absorbed onto carbon and used to oxidize aniline while reducing the Pt(NH 3 ) 4 2+ itself. The Pt and PANI were thoroughly mixed together throughout the entire polymerization process. Accordingly, nearly all of the Pt NPs in the prepared Pt/PANI/C composite, except those present on the outermost catalyst layer, were embedded inside the PANI rather than exposed to the outside. Thus, some of the Pt NPs could not be utilized by the fuel cell, and the Pt/PANI/ C composites showed poor oxygen reduction reaction (ORR) activity; indeed, no Pt behavior was observed in cyclic voltammograms (CVs) of ...

In this paper, we show that the surface tension of charge-stabilized titania suspensions strongly depends on the particle concentration. The surface tension first decreases significantly with an increase in the weight percent and then increases with a further increase in the weight percent. Thermodynamic arguments are used to explain the initial decrease in the surface tension for lower particle concentrations. For higher concentrations, it is hypothesized that the capillary forces acting between the immersed particles at the interface cause the increase in the surface tension.

In this paper, the adsorption energy of an acicular (prolate and cylindrical) particle onto a liquid-fluid interface and the effect of the line tension are investigated. The results show that, without line tension, acicular particles always prefer to lie flat in the plane of the interface. However, line tension plays a significant role in determining the adsorption of an acicular particle. First, the line tension creates an energy barrier for the adsorption of particles onto an interface. The planar configuration has a larger energy barrier due to the longer contact line. Therefore, the particles prefer to enter the interface in a homeotropic configuration and then rearrange to a planar configuration or an oblique configuration with a small tilt angle. Second, for prolate particles, an energy maximum occurs at some tilt angles when the line tension is large. Therefore, once the prolate particle is adsorbed on the interface in a homeotropic configuration or with a larger tilt angle, it must conquer an energy barrier to rearrange to a planar configuration. For cylindrical particles, when the line tension is higher, the planar configuration will not be the most energy-favorable configuration. The cylindrical particles prefer to stay in the interface with a small tilt angle.

High dispersion Pt nanoparticles supported on surface thiolation functional carbon nanotubes (SH-CNTs) is presented and electrochemical measurements confirm that the Pt/SH-CNTs catalyst shows good durability and excellent ORR activity.

No abstract

The maximizing daily freshwater yield on the ocean surface necessitates allday water harvesting technologies and materials. This is realizable by taking advantage of the natural sunlight and humid air, which can drive daytime solar desalination and nighttime fog collection, respectively. To this end, two types of hierarchically porous microneedle array structures, which demonstrate superior capabilities for efficient fog capturing and photothermal evaporation, respectively, are prepared. The gel-forged microneedle arrays with Janus wettability are fabricated via a simple and controllable top-down micro-molding process on a porous platform, and porosity within microneedles is further achieved readily by additional freeze-drying treatment. The developed microneedle structure shows an ultrahigh fog harvesting rate up to 30.5 kg m −2 h −1 , enabling high flux water droplet harvesting from moisture during nighttime. In the daytime, a solar evaporation rate of 2.46 kg m −2 h −1 is realized due to the increased evaporative area of the porous microneedle arrays and enhanced photothermal conversion. By uniting these two waterharvesting routes, a daily cycle can ideally deliver an overall water yield close to 200 kg m −2 , which will offer a promising solution for sustaining future lowcost and decentralized clean water production.

No abstract

In this work, a conjugated polymer PNV is developed, linking naphthalene diimide with a vinyl linkage. Owing to the C-HO hydrogen bond between the carbonyl and the vinyl, PNV exhibits a high red emission with a quantum yield of 33.4% in the solid state while it shows n-type properties with an electron mobility up to 1.5 × 10 cm V s in organic field effect transistors, simultaneously.