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.

Bifunctional 2D superlattice electrocatalysts of alternating layered double hydroxide (LDH)−transition metal dichalcogenide (TMD) heterolayers were synthesized by interstratification of the exfoliated nanosheets. Density functional theory calculations predict an increased interfacial charge transfer between interstratified LDH and TMD nanosheets, which would lead to enhanced electrocatalytic activity. The electrostatically driven self-assembly of oppositely charged 2D building blocks, i.e., exfoliated Ni−Al-LDH/Ni−Fe-LDH and MoS 2 nanosheets, yields mesoporous heterolayered Ni−Al-LDH−MoS 2 /Ni−Fe-LDH−MoS 2 superlattices. The synthesized superlattices show improved electrocatalytic activity with enhanced durability for oxygen and hydrogen evolution reactions and water splitting. The interstratification improves the chemical stability of LDH in acidic media, thus expanding its possible applications. The high electrocatalytic activity of the superlattices may be attributed to an enhanced affinity for OH − /H + , improved electrical conduction and charge transfer, and the increase of active sites. This study indicates that the formation of superlattices via self-assembly of 2D nanosheets provides useful methodology to explore high-performance electrocatalysts with improved stability.

Orthorhombic GaFeO 3 (o-GFO) with the polar Pna2 1 space group is a prominent ferrite owing to its piezoelectricity and ferrimagnetism, coupled with magnetoelectric effects. Herein, we demonstrate large ferroelectric remanent polarization in undoped o-GFO thin films by adopting either a hexagonal strontium titanate (STO) or a cubic yttrium-stabilized zirconia (YSZ) substrate. The polarization-electric-field hysteresis curves of the polar c-axis-grown o-GFO film on a SrRuO 3 /STO substrate show the net switching polarization of~35 μC cm − 2 with an unusually high coercive field (E c ) of ± 1400 kV cm − 1 at room temperature. The positive-up and negative-down measurement also demonstrates the switching polarization of~26 μC cm − 2 . The activation energy for the polarization switching, as obtained by density-functional theory calculations, is remarkably high, 1.05 eV per formula unit. We have theoretically shown that this high value accounts for the extraordinary high E c and the stability of the polar Pna2 1 phase over a wide range of temperatures up to 1368 K.

Polymeric microlens arrays, with a diameter of 36–96 μm, a radius of curvature of 20–60 μm and a pitch of 250 μm, were fabricated using micro-compression molding with electroformed mold inserts. We used the reflow method and the electroforming process to make the mother and the metallic mold inserts, respectively. Micro-compression molding with powder polymer was developed to replicate microlenses. The surface profiles, imaging qualities, and surface roughness of the microlenses were measured and analyzed.

A facile synthesis of highly stable, water-dispersible metal-nanoparticle-decorated polymer nanocapsules (M@CB-PNs: M = Pd, Au, and Pt) was achieved by a simple two-step process employing a polymer nanocapsule (CB-PN) made of cucurbit [6]uril (CB[6]) and metal salts. The CB-PN serves as a versatile platform where various metal nanoparticles with a controlled size can be introduced on the surface and stabilized to prepare new water-dispersible nanostructures useful for many applications. The Pd nanoparticles on CB-PN exhibit high stability and dispersibility in water as well as excellent catalytic activity and recyclability in carbon-carbon and carbon-nitrogen bond-forming reactions in aqueous medium suggesting potential applications as a green catalyst.Metal nanoparticles (NPs) have attracted great attention because their unique properties such as high surface to volume ratio, quantum confinement, and surface plasmon effect can contribute to diverse applications in catalysis, nanoelectronics, molecular imaging, biosensors, and nanomedicine. [1] Many of these intriguing properties strongly depend on the size [2] and surface area [3] of the NPs. In addition, support materials (or stabilizers) [4] such as polymers, [5] dendrimers, [6] silica, [7] and metal oxides, [8] which are required for some applications (e.g. heterogeneous catalysis), also affect the properties of NPs. Although NPs on solid supports have been successfully employed in catalysis, most systems suffer from shortcomings such as passivation of the NP surface, [9] lack of long-term stability, [10] low dispersibility, [11] deactivation or constant leaching, [12] and low recyclability which limit their capacity and applications. [13] For example, NPs supported on mesoporous/modified silica are unstable, which leads to a rapid decay of the catalytic activity under the reaction conditions. [12] Furthermore, the catalytic activity and stability of NPs in environmentally benign media such as water has important environmental, economical, and safety implications, which are crucial in green chemistry. [14] However, to date, catalysis using NPs on solid supports has seldom been explored in water. [15] Cucurbit[n]uril (CB[n]: n = 5-8, 10) exhibits remarkable recognition abilities with high affinity and selectivity towards organic and inorganic species [16] and stabilizes NPs by forming a passive layer or acting as a protecting agent. [17] We recently reported hollow polymer nanocapsules (CB-PNs) with a thin shell composed of covalently linked cucurbit[6]uril (CB[6]) units, [18] which can be readily synthesized from commercially available allyloxyCB[6] and dithiol (3,6-dioxa-1,8-octanedithiol) in a one-pot reaction. Unique features of CB-PNs include facile tailoring of their surface to prepare new functional materials for various applications such as targeted drug delivery, diagnosis, and imaging. [18c,d] Moreover, CB-PNs synthesized in the presence of excess dithiol have "disulfide loops" protruding from the surface, [18a,b, 19] which can be used as an i...