Ultra-stable Pt cathode catalysts in ultra-low Pt loading proton exchange membrane fuel cells were synthesized by facile carbon encapsulation.

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Three-dimensional, ordered macroporous materials such as inverse opal structures are attractive materials for various applications in electrochemical devices because of the benefits derived from their periodic structures: relatively large surface areas, large voidage, low tortuosity and interconnected macropores. However, a direct application of an inverse opal structure in membrane electrode assemblies has been considered impractical because of the limitations in fabrication routes including an unsuitable substrate. Here we report the demonstration of a single cell that maintains an inverse opal structure entirely within a membrane electrode assembly. Compared with the conventional catalyst slurry, an ink-based assembly, this modified assembly has a robust and integrated configuration of catalyst layers; therefore, the loss of catalyst particles can be minimized. Furthermore, the inverse-opalstructure electrode maintains an effective porosity, an enhanced performance, as well as an improved mass transfer and more effective water management, owing to its morphological advantages.

Tin oxide-based materials, operating via irreversible conversion and reversible alloying reaction, are promising lithium storage materials due to their higher capacity. Recent studies reported that nanostructured SnO 2 anode provides higher capacity beyond theoretical capacity based on the alloying reaction mechanism; however, their exact mechanism remains still unclear. Here, we report the detailed lithium storage mechanism of an ordered mesoporous SnO 2 electrode material. Synchrotron X-ray diffraction and absorption spectroscopy reveal that some portion of Li 2 O decomposes upon delithiation and the resulting oxygen reacts with Sn to form the SnO x phase along with dealloying of Li x Sn, which are the main reasons for unexpected high capacity of an ordered mesoporous SnO 2 material. This finding will not only be helpful in a more complete understanding of the reaction mechanism of Sn-based oxide anode materials but also will offer valuable guidance for developing new anode materials with abnormal high capacity for next generation rechargeable batteries. ■ INTRODUCTIONLithium-ion batteries have been recognized as one of the most promising power source for various applications including portable electronics, electric vehicles, and power storage systems of renewable energy. 1 Major challenges of lithium ion batteries for these applications include high energy density, excellent capacity retention, safety, and low cost. 1−3 In order to achieve higher energy density of lithium ion battery than that of currently commercialized lithium ion battery, 4−7 metal oxides are being investigated as alternative anode materials due to their high energy density achieved by conversion and alloying reactions. 8,9 Especially, tin oxide-based materials, including SnO and SnO 2 , are being considered as one of the best anode materials due to their higher specific lithium storage capacities. 10 Previous studies show that SnO 2 goes through an irreversible conversion reaction during the initial cycle, which leads to formation of Sn metal and Li 2 O matrix, followed by a reversible alloying/dealloying reaction of Sn with lithium. 11−17

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A substantial amount of research effort has been directed toward the development of Pt-based catalysts with higher performance and durability than conventional polycrystalline Pt nanoparticles to achieve high-power and innovative energy conversion systems. Currently, attention has been paid toward expanding the electrochemically active surface area (ECSA) of catalysts and increase their intrinsic activity in the oxygen reduction reaction (ORR). However, despite innumerable efforts having been carried out to explore this possibility, most of these achievements have focused on the rotating disk electrode (RDE) in half-cells, and relatively few results have been adaptable to membrane electrode assemblies (MEAs) in full-cells, which is the actual operating condition of fuel cells. Thus, it is uncertain whether these advanced catalysts can be used as a substitute in practical fuel cell applications, and an improvement in the catalytic performance in real-life fuel cells is still necessary. Therefore, from a more practical and industrial point of view, the goal of this review is to compare the ORR catalyst performance and durability in half- and full-cells, providing a differentiated approach to the durability concerns in half- and full-cells, and share new perspectives for strategic designs used to induce additional performance in full-cell devices.

Pt-based bimetallic nanoparticles have attracted significant attention as a promising replacement for expensive Pt nanoparticles. In the systematic design of bimetallic nanoparticles, it is important to understand their preferred atomic structures. However, compared with unary systems, alloy nanoparticles present more structural complexity with various compositional configurations, such as mixed-alloy, core-shell, and multishell structures. In this paper, we developed a unified empirical potential model for various Pt-based binary alloys, such as Pd-Pt, Cu-Pt, Au-Pt, and Ag-Pt. Within this framework, we performed a series of Monte Carlo (MC) simulations that quantify the energetically favorable atomic arrangements of Pt-based alloy nanoparticles: an intermetallic compound structure for the Pd-Pt alloy, an onion-like multi-shell structure for the Cu-Pt alloy, and core-shell structures (Au@Pt and Ag@Pt) for the Au-Pt and Ag-Pt alloys. The equilibrium nanoparticle structures for the four alloy types were compared with each other, and the structural features can be interpreted by the interplay of their material properties, such as the surface energy and heat of formation. PACS numbers: 61.46.+w, 36.40.Ei, 64.70.Nd I. II. INTERATOMIC POTENTIAL MODEL A. Embedded atom method potentials for Pt, Pd, and novel metals (Ag, Au, Cu)

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