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Pt overlayers were deposited on carbon-supported Ir nanoparticles with various coverages. Structural and electrochemical characterizations were performed using transmission electron microscopy (TEM), X-ray diffraction, high-resolution powder diffraction (HRPD), X-ray photoelectron spectroscopy (XPS), X-ray absorption near-edge spectroscopy (XANES), cyclic voltammetry (CV), CO stripping voltammetry, and N2O reduction. The surface of Ir nanoparticles was covered with Pt overlayers with thickness varying from the submonolayer scale to more than two monolayers. Surface analyses such as CV and CO stripping voltammetry indicated that the Pt overlayers were uniformly deposited on the Ir nanoparticles, and the resultant Pt overlayers exhibited gradual changes in surface characteristics toward the Pt surface as the surface coverage increased. The distinct CO stripping characteristics and the enhanced Pt utilization affected electrocatalytic activities for methanol oxidation. The electrochemical stability of the Pt overlayer was compared with a commercial carbon-supported Pt catalyst by conducting a potential cycling experiment. [ABSTRACT FROM AUTHOR]

Pt-based multistructured nanocatalysts such as alloy, core-shell, and surface Pt-rich nanoparticles have been extensively studied for hydrogen fuel cell applications, and their catalytic performances for oxygen reduction reactions have been significantly upgraded for decades. Due to these technical enhancements, Pt-based nanoarchitectures have turned out to be compatible with commercially accessible fuel cell systems. In addition, based on physical and electrochemical backgrounds for the basic catalyst nanoarchitectures, novel catalyst designs with organic-inorganic hybrid concepts have been recently developed to more effectively improve the electrochemical reaction activities and durabilities. In this review, the typical class of Pt-based nanocatalysts are systematically explained according to their compositions and structures, and the emerging class of organic-inorganic hybrid catalyst designs are then thoroughly introduced. It is expected that the most recent improvements of Pt-based nanoarchitectures will have great effects on the future works for the commercialization of fuel cell catalysts. [ABSTRACT FROM AUTHOR]

Ru and Pt−Ru (Pt:Ru = 1:1) nanoparticles supported on carbon black were prepared by the borohydride reduction method using oleylamine as a stabilizer in an anhydrous ethanol solvent. We investigated the effect of Pt segregation to the surface of alloy nanoparticles on the methanol oxidation reaction (MOR). As-prepared Pt1Ru1/C showed a narrow size distribution and a relatively uniform particle distribution on a carbon support. However, its electrocatalytic activity toward the MOR was poor due to the high surface concentration of Ru. As duration time of heat treatment at 200 °C was increased up to 2 h, the surface composition of Pt atoms was increased without significant particle growth due to thermally induced segregation of Pt atoms, which were revealed by TEM images, X-ray photoelectron spectroscopy (XPS) analysis, changes in the potentials of zero total charge (pztc), and increase in the oxidation charge of “reduced CO2”. In particular, from the combination of CO adlayer oxidation and “reduced CO2” oxidation charges, the increased surface concentration of Pt of alloy catalysts was relatively quantified when compared to its as-prepared state. Cyclic voltammograms in 0.1 M HClO4solution with 0.5 M methanol showed that Pt1Ru1/C annealed for 2 h at 200 °C in a flow of mixture gas of Ar and H2(5 vol %) had a less positive onset potential for the MOR. These results demonstrate a definitive contribution from segregation of Pt atoms to the MOR activity. [ABSTRACT FROM AUTHOR]

Demand on the practical synthetic approach to the high performance electrocatalyst is rapidly increasing for fuel cell commercialization. Here we present a synthesis of highly durable and active intermetallic ordered face-centered tetragonal (fct)-PtFe nanoparticles (NPs) coated with a "dual purpose" N-doped carbon shell. Ordered fct-PtFe NPs with the size of only a few nanometers are obtained by thermal annealing of polydopamine-coated PtFe NPs, and the N-doped carbon shell that is in situ formed from dopamine coating could effectively prevent the coalescence of NPs. This carbon shell also protects the NPs from detachment and agglomeration as well as dissolution throughout the harsh fuel cell operating conditions. By controlling the thickness of the shell below 1 nm, we achieved excellent protection of the NPs as well as high catalytic activity, as the thin carbon shell is highly permeable for the reactant molecules. Our ordered fct-PtFe/C nanocatalyst coated with an N-doped carbon shell shows 11.4 times-higher mass activity and 10.5 times-higher specific activity than commercial Pt/C catalyst. Moreover, we accomplished the long-term stability in membrane electrode assembly (MEA) for 100 h without significant activity loss. From in situ XANES, EDS, and first-principles calculations, we confirmed that an ordered fct-PtFe structure is critical for the long-term stability of our nanocatalyst. This strategy utilizing an N-doped carbon shell for obtaining a small ordered-fct PtFe nanocatalyst as well as protecting the catalyst during fuel cell cycling is expected to open a new simple and effective route for the commercialization of fuel cells. [ABSTRACT FROM AUTHOR]

Vertical and lateral heterogeneous structures of two-dimensional (2D) materials have paved the way for pioneering studies on the physics and applications of 2D materials. A hybridized hexagonal boron nitride (h-BN) and graphene lateral structure, a heterogeneous 2D structure, has been fabricated on single-crystal metals or metal foils by chemical vapor deposition (CVD). However, once fabricated on metals, the h-BN/graphene lateral structures require an additional transfer process for device applications, as reported for CVD graphene grown on metal foils. Here, we demonstrate that a single-crystal h-BN/graphene lateral structure can be epitaxially grown on a wide-gap semiconductor, SiC(0001). First, a single-crystal h-BN layer with the same orientation as bulk SiC was grown on a Si-terminated SiC substrate at 850 °C using borazine molecules. Second, when heated above 1150 °C in vacuum, the h-BN layer was partially removed and, subsequently, replaced with graphene domains. Interestingly, these graphene domains possess the same orientation as the h-BN layer, resulting in a single-crystal h-BN/graphene lateral structure on a whole sample area. For temperatures above 1600 °C, the single-crystal h- BN layer was completely replaced by the single-crystal graphene layer. The crystalline structure, electronic band structure, and atomic structure of the h-BN/graphene lateral structure were studied by using low energy electron diffraction, angle-resolved photoemission spectroscopy, and scanning tunneling microscopy, respectively. The h-BN/graphene lateral structure fabricated on a wide-gap semiconductor substrate can be directly applied to devices without a further transfer process, as reported for epitaxial graphene on a SiC substrate. [ABSTRACT FROM AUTHOR]

Described herein is the development of a novel Co-based oxygen electrode catalyst coupled with unique carbon structures. The present carbon shell coated Co nanoparticles of which the surface composites are modified by phosphorus incorporation, exhibit efficient oxygen reduction activities as well as oxygen evolving properties. [ABSTRACT FROM AUTHOR]

We propose a method to enhance the fuel cell efficiency with the simultaneous removal of toxic heavy metal ions. Carbon monoxide (CO), an intermediate of methanol oxidation that is primarily responsible for Pt catalyst deactivation, can be used as an in-situ reducing agent for hexavalent chromium (Cr (VI)) with reactivating the CO-poisoned Pt catalyst. Using electro-oxidation measurements, the oxidation of adsorbed CO molecules coupled with the concurrent conversion of Cr (VI) to Cr (III) was confirmed. This concept was also successfully applied to a methanol fuel cell to enhance its performance efficiency and to remove toxic Cr (VI) at the same time. [ABSTRACT FROM AUTHOR]

This paper describes how primary contaminants in ambient air affect the performance of the cathode in fuel cell electric vehicle applications. The effect of four atmospheric pollutants (SO2, NH3, NO2, and CO) on cathode performance was investigated by air impurity injection and recovery test under load. Electrochemical analysis via polarization and electrochemical impedance spectroscopy was performed for various concentrations of contaminants during the impurity test in order to determine the origins of performance decay. The variation in cell voltage derived empirically in this study and data reported in the literature were normalized and juxtaposed to elucidate the relationship between impurity concentration and performance. Mechanisms of cathode degradation by air impurities were discussed in light of the findings. [ABSTRACT FROM AUTHOR]

The properties of Pt-Ni nanostructures were successfully controlled by employing different Pt precursors in the preparation of Pt-Ni nanocomposites, which were synthesized by a co-reducing Pt and Ni precursors. Pt-Ni nanostructures were obtained by leaching Ni species from the Pt-Ni nanocomposite. The use of H2PtCl6 as a precursor yielded aggregated small Pt particles, while [Pt(NH3)4]Cl2 yielded large hollow Pt nanostructures. A possible mechanism leading to the morphological difference between the two structures was suggested. Owing to a higher electrochemically active surface area and a favorable surface structure, hollow Pt nanostructures from the [Pt(NH3)4]Cl2 precursor showed significantly better performance in ammonia oxidation than the aggregated Pt particles resulting from the H2PtCl6 precursor. [ABSTRACT FROM AUTHOR]

The design of electrocatalysts for polymer electrolyte membrane fuel cells must satsify two equally important fundamental principles: optimization of electrocatalytic activity and long-term stability in acid media (pH <1) at high potential (0.8 V). We report here a solution-based approach to the preparation of Pt-based alloy with early transition metals and realistic parameters for the stability and activity of Pt3M (M = Y, Zr, Ti, Ni, and Co) nanocatalysts for oxygen reduction reaction (ORR). The enhanced stability and activity of Pt-based alloy nanocatalysts in ORR and the relationship between electronic structure modification and stability were studied by experiment and DFT calculations. Stability correlates with the d-band fillings and the heat of alloy formation of Pt3M alloys, which in turn depends on the degree of the electronic perturbation due to alloying. This concept provides realistic parameters for rational catalyst design in Pt-based alloy systems. [ABSTRACT FROM AUTHOR]