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.

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 Pt(3)M (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 Pt(3)M 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.

Antireflection (AR) coatings are indispensable requirements for many optical applications such as flat-panel displays, solar cells, lasers, and other optoelectronic devices. [1±4] Two approaches are available as model methods for achieving low surface reflectivity: 1) Fabrication of nanoporous layers using a particle coating, [5] phase separation of a binary polymer blend, [6] and polyelectrolyte multilayer coating. [7] These thin dielectric films with a low refractive index can improve light transmission via the destructive interference of the reflected light at the air±film and the film±substrate interfaces; 2) Fabrication of surface relief structures using holographic lithography, reactive-ion etching, [8] and plate embossing.[9] The array of conical protuberances having sinusoidal profiles cause variations in the refractive index between the air and substrate to be gradual, dramatically reducing the reflection losses at the surface. The former has considerable advantages in cost efficiency, a factor that is basically attributable to the simpler fabrication process involved. However, a lack of controllable factors relative to surface morphology, for example, domain size and air content, is a major drawback of this approach. In designing AR surfaces, it is important to have the surface structures under control, so as to tune the desired wavelength for peak performance.The latter approach, involving surface relief gratings, has many tunable factors, such as the grating spacing, depth, and cross-sectional geometry, in contrast to the former approach. In addition, it is well-known that such relief structures having a periodic sub-wavelength protuberance can behave as an ideal antireflection coating with nearly zero reflectance over a large range of wavelengths and fields of view.[10] These structures are commonly referred to as ªmotheyeº structures, because they have the same geometry as the corneal lenses of night-flying moths. In this communication, we report on attempts to design motheye-like colloidal patterns on a surface in an unprecedented way. Our approach is based on the layer-by-layer (LbL) self-assembly method [11] and consists of alternating layers of charged polymer colloids and polyelectrolytes (PE). Numerous approaches have been reported regarding the array of colloids over charged templates by the LbL approach.[12±16] Recently, colloidal coating as an AR surface has also been demonstrated to be a convenient and economical process.[5] Herein, we demonstrate that the AR efficiency of the colloidal layer can be improved by a novel colloid-on-colloid stamping method, which changes the common colloidal layer into a motheye-like structure with a graded index. A schematic representation of the fabrication process is illustrated in Figure 1. The process starts with a glass substrate on which a PE multilayer is grown by means of the LbL technique. The construction of this multilayer only requires alternate immersion of the substrate into aqueous solutions of the polycation, poly(allylamine hydrochloride)...

Compared to nanostructured platinum (Pt) catalysts, ordered Pt-based intermetallic nanoparticles supported on a carbon substrate exhibit much enhanced catalytic performance, especially in fuel cell electrocatalysis. However, direct synthesis of homogeneous intermetallic alloy nanocatalysts on carbonaceous supports with high loading is still challenging. Herein, we report a novel synthetic strategy to directly produce highly dispersed MPt alloy nanoparticles (M = Fe, Co, or Ni) on various carbon supports with high catalyst loading. Importantly, a unique bimetallic compound, composed of [M­(bpy)3]2+ cation (bpy = 2,2′-bipyridine) and [PtCl6]2– anion, evenly decomposes on carbon surface and forms uniformly sized intermetallic nanoparticles with a nitrogen-doped carbon protection layer. The excellent oxygen reduction reaction (ORR) activity and stability of the representative reduced graphene oxide (rGO)-supported L10-FePt catalyst (37 wt %-FePt/rGO), exhibiting 18.8 times higher specific activity than commercial Pt/C catalyst without degradation over 20 000 cycles, well demonstrate the effectiveness of our synthetic approach toward uniformly alloyed nanoparticles with high homogeneity.