PtRu bimetallic particles are well-known commercial catalysts with promising performance for methanol oxidation. However, shape-controlled synthesis of PtRu bimetallic nanocrystals, especially for the platonic structures with {100} (e.g., cubes) or {111} facets (e.g., icosahedra) exposed towards catalysis, has met only limited success due to the different crystal structures of Pt and Ru. Here we report a facile approach to the synthesis of Ru decorated Pt bimetallic cubes and icosahedra in a mixed solvent. We found that the cubes were formed in the solvent containing N,N-dimethylmethanamide (DMF) and oleylamine (OAm) possibly due to the selective adsorption of CO on Pt{100} arising from the decomposition of DMF catalyzed by a Ru salt precursor. When hexadecane was added into the aforementioned solvent, the synthesis became a two-phase interfacial reaction due to the large difference in solvent polarity, thereby retarding the reaction kinetics and promoting the formation of the icosahedra with the composition similar to the cubes. When evaluated as catalysts towards methanol oxidation, the Ru decorated Pt icosahedra showed much better performance in terms of specific and mass activity relative to the corresponding cubes. Specifically, the Ru decorated Pt bimetallic icosahedra achieved a specific activity of 0.76 mA cm(-2) and mass activity of 74.43 mA mgPt(-1), which is ∼6.7 and 2.2 times as high as those of the carbon supported Pt7Ru nanoparticles, respectively. This enhancement can be attributed to a combination of twin-induced strain and facet effects.

PtCu alloy nanocrystals, especially for the PtCu 3 component, hold great potential as catalysts in methanol oxidation reaction (MOR) owing to their promising catalytic properties arising from the bifunctional mechanism associated with Pt and Cu sites. However, Pt and Cu salt precursors are difficult to be co-reduced in a synthesis due to the large difference in their redox potential, because of which Pt or Cu nanocrystals are initially generated and then evolve into a PtCu alloy with remarkable variation of the PtCu component by underpotential deposition (UPD) and galvanic replacement, respectively. Here we report a facile method for the shape-controlled synthesis of PtCu 3 alloy nanocrystals by co-reduction of Pt and Cu salt precursors using oleylamine (OAm) and N,N-dimethylformamide (DMF) as co-reducing agents at different temperatures. PtCu 3 alloy hexapods with preferential overgrowth along the <100> direction are obtained at 220 °C through co-reduction reaction accompanied by Cl − ion induced underpotential deposition (UPD).Meanwhile, galvanic replacement between PtCu 3 alloy nanocrystals and the Pt precursor co-exists with overgrowth induced by co-reduction reaction at 190 °C, eventually resulting in PtCu 3 hollow nanoframes.Both the PtCu 3 alloy hexapods and hollow nanoframes exhibit remarkably enhanced catalytic properties in terms of activity and stability towards MOR relative to the commercial Pt/C. Specifically, the PtCu 3 alloy hexapods and hollow nanoframes show the highest specific (2.96 mA cm −2 ) activity and mass activity (1.861 mA μg Pt −1) for MOR, respectively, which are 13.5 and 24.2 times higher than those of the commercial Pt/C. This enhancement can be attributed to their unique structures and the possible bifunctional mechanism between Pt and Cu.

Anisotropic Au nanoparticles show unique localized surface plasmon resonance (LSPR) properties, which make it attractive in optical, sensing, and biomedical applications. In this contribut ion, we report a general and facile strategy towards aqueous synthesis of Au and M@Au (M = Pd, CuPt) hybrid nanostars by reducing HAuCl4 with ethanolamine in the presence of cetyltrimethylammonium bromide (CTAB). According to electron microscopic observati on and spectral monitoring, we found that the layered epitaxial growth mode (i.e., Frank-van der Merwe mechanism) contributes to the enlargement of the core, while, the random attachment of Au nanoclusters onto the cores accounts for the formation of the branches. Both of them are indispensable for the formation of the nanostars. The LSPR properties of the Au nanoparticles have been well investigated with morphology control via precursor amount and growth temperature. The Au nanostars showed improved surfac e-enhanced Raman spectroscopy (SERS) performance for rhodamine 6G due to their sharp edges and tips, which were therefore confirmed as good SERS substrate to detect trace amount of molecules.

A posteriori error estimates of semidiscrete mixed finite element methods for quadratic optimal control problems involving linear parabolic equations are developed. The state and co-state are discretised by Raviart-Thomas mixed finite element spaces of order k, and the control is approximated by piecewise polynomials of order k (k ≥ 0). We derive our a posteriori error estimates for the state and the control approximations via a mixed elliptic reconstruction method. These estimates seem to be unavailable elsewhere in the literature, although they represent an important step towards developing reliable adaptive mixed finite element approximation schemes for the control problem.