We report a general approach to NiAu alloy nanoparticles (NPs) by co-reduction of Ni(acac)2 (acac = acetylacetonate) and HAuCl4·3H2O at 220 °C in the presence of oleylamine and oleic acid. Subject to potential cycling between 0.6 and 1.0 V (vs reversible hydrogen electrode) in 0.5 M H2SO4, the NiAu NPs are transformed into core/shell NiAu/Au NPs that show much enhanced catalysis for hydrogen evolution reaction (HER) with Pt-like activity and much robust durability. The first-principles calculations suggest that the high activity arises from the formation of Au sites with low coordination numbers around the shell. Our synthesis is not limited to NiAu but can be extended to FeAu and CoAu as well, providing a general approach to MAu/Au NPs as a class of new catalyst superior to Pt for water splitting and hydrogen generation.

We report a simple yet general approach to monodisperse MPt (M = Fe, Co, Ni, Cu, Zn) nanoparticles (NPs) by coreduction of M(acac)2 and Pt(acac)2 (acac = acetylacetonate) with oleylamine at 300°C. In the current reaction condition, oleylamine serves as the reducing agent, surfactant, and solvent. As an example, we describe in details the synthesis of 9.5 nm CoPt NPs with their compositions controlled from Co37Pt63 to Co69Pt31. These NPs show composition-dependent structural and magnetic properties. The unique oleylamine reduction process makes it possible to prepare MPt NPs with their physical properties and surface chemistry better rationalized for magnetic or catalytic applications. Keywords: nanoparticles, oleylamine reduction, MPt alloy, alloy structure, nanomagnetism, catalysis Y U E T A L . , N A N O L E T T E R S 1 4 ( 2 0 1 4 )2 MPt nanoparticles (NPs) with M = Mn, Fe, Co, Ni, or Cu have attracted much attention in recent years due to their strong ferromagnetism (from FePt and CoPt) 1−6 and their much enhanced catalysis for electrochemical reactions. 6−15 These alloy NPs with controlled sizes and compositions are now routinely prepared either by decomposition/reduction of metal carbonyls and metal salts, or by coreduction of two metal salts. Despite the nearly precise control achieved on NP sizes and compositions, each of these previous syntheses is specific for one typical kind of MPt NPs. For example, thermal decomposition of Fe(CO)5 and reduction of Pt(acac)2 (acac = acetylacetonate) is commonly used to prepare monodisperse FePt NPs with Fe/Pt composition controls. 16−22 When this reaction is applied to prepare CoPt NPs via decomposition of Co2(CO)8 and reduction of Pt(acac)2, only Pt-rich CoPt NPs can be produced. 23,24 The same is true for the synthesis of MnPt via decomposition of Mn2(CO)10 and reduction of Pt(acac)2. 25,26 To prepare other types of MPt (M = Ni, Cu) NPs, metal salt coreduction has to be used because Ni and Cu carbonyls are not readily available. 27−29 In principle, metal salt reduction reaction should be a general approach to different MPt NPs, but the reduction potential differences between M-and Pt-salts and the need to control MPt nucleation and growth often require the use of a specific reducing agent for each synthesis. 30−32 Considering the sensitivity of MPt NP magnetism and catalysis over M/Pt compositions and surface chemistry, it is important to have a generalized synthetic process so that each kind of MPt NPs can be prepared in a very similar reaction condition and their magnetic and catalytic properties can be better controlled and compared.Here, we report a facile, yet general, synthesis of monodisperse MPt (M = Fe, Co, Ni, Cu, Zn) alloy NPs via oleylamine (OAm) reduction of M(acac)2 and Pt(acac)2. OAm is widely used in the solution phase synthesis of NPs. 33 It is a primary amine with the boiling point around 350°C. Its −NH2 group has a relatively weak binding power to transition metals, especially to later transition metals. This, plus its long hydrocarbon...

A simple process to prepare monodisperse ferrimagnetic cobalt-substituted magnetite Co(x)Fe(3-x)O4 nanoparticles is reported. These ferrimagnetic nanoparticles are readily dispersed in hexane, forming a stable ferrimagnetic nanoparticle dispersion, and allowing easy nanoparticle self-assembly. When assembled under an external magnetic field (5.5 kOe), these nanoparticles show preferred magnetic alignment with their H(c) reaching 2.49 kOe.

A facile approach to bimetallic phosphides, Co-Fe-P, by a high-temperature (300 °C) reaction between Co-Fe-O nanoparticles and trioctylphosphine is presented. The growth of Co-Fe-P from the Co-Fe-O is anisotropic. As a result, Co-Fe-P nanorods (from the polyhedral Co-Fe-O nanoparticles) and sea-urchin-like Co-Fe-P (from the cubic Co-Fe-O nanoparticles) are synthesized with both the nanorod and the sea-urchin-arm dimensions controlled by Co/Fe ratios. The Co-Fe-P structure, especially the sea-urchin-like (Co(0.54)Fe(0.46))2P, shows enhanced catalysis for the oxygen evolution reaction in KOH with its catalytic efficiency surpassing the commercial Ir catalyst. Our synthesis is simple and may be readily extended to the preparation of other multimetallic phosphides for important catalysis and energy storage applications.

We report a one-pot synthesis of urchin-like FePd-Fe3O4 nanocomposites, spherical clusters of FePd nanoparticles (NPs) with spikes of Fe3O4 nanorods (NRs), via controlled thermal decomposition of Fe(CO)5 and reduction of Pd(acac)2. The FePd NPs with sizes between 6 and 9 nm self-aggregate into 60 nm superparticles (SPs), and Fe3O4 NRs grow on the surface of these SPs. Reductive annealing at 500 °C converts the FePd-Fe3O4 into exchange-coupled nanocomposites L1(0)-FePd-Fe with their Hc tunable from 0.8 to 2.6 kOe and Ms controlled from 90 to 190 emu/g. The work provides a general approach to L1(0)-FePd-Fe nanocomposite magnets for understanding exchange coupling at the nanoscale. The concept may be extended to other magnetic nanocomposite systems and may help to build superstrong magnets for magnetic applications.

We report a new strategy of controlling catalytic activity and selectivity of Cu nanoparticles (NPs) for the ammonia borane initiated hydrogenation reaction. Cu NPs are active and selective for chemoselective reduction of nitrostyrene to vinylaniline under ambient conditions. Their activity, selectivity, and more importantly, stability are greatly enhanced by their anchoring on WO 2.72 nanorods, providing a room-temperature full conversion of nitrostyrene selectively to vinylaniline (>99% yield). Compared with all other catalysts developed thus far, our new Cu/WO 2.72 catalyst shows much enhanced hydrogenation selectivity and stability without the use of pressured hydrogen. The synthetic approach demonstrated here can be extended to prepare various M/WO 2.72 catalysts (M = Fe, Co, Ni), with M being stabilized for many chemical reactions.

We report a general chemical approach to synthesize strongly ferromagnetic rare‐earth metal (REM) based SmCo and SmFeN nanoparticles (NPs) with ultra‐large coercivity. The synthesis started with the preparation of hexagonal CoO+Sm2O3 (denoted as SmCo‐O) multipods via decomposition of Sm(acac)3 and Co(acac)3 in oleylamine. These multipods were further reduced with Ca at 850 °C to form SmCo5 NPs with sizes tunable from 50 to 200 nm. The 200 nm SmCo5 NPs were dispersed in ethanol, and magnetically aligned in polyethylene glycol (PEG) matrix, yielding a PEG‐SmCo5 NP composite with the room temperature coercivity (Hc) of 49.2 kOe, the largest Hc among all ferromagnetic NPs ever reported, and saturated magnetic moment (Ms) of 88.7 emu g−1, the highest value reported for SmCo5 NPs. The method was extended to synthesize other ferromagnetic NPs of Sm2Co17, and, for the first time, of Sm2Fe17N3 NPs with Hc over 15 kOe and Ms reaching 127.9 emu g−1. These REM based NPs are important magnetic building blocks for fabrication of high‐performance permanent magnets, flexible magnets, and printable magnetic inks for energy and sensing applications.

A crucial issue restricting the application of direct alcohol fuel cells (DAFCs) is the low activity of Pt‐based electrocatalysts for alcohol oxidation reaction caused by the reaction intermediate (CO*) poisoning. Herein, a new strategy is demonstrated for making a class of sub‐monolayer YOx/MoOx‐surface co‐decorated ultrathin platinum nanowires (YOx/MoOx–Pt NWs) to effectively eliminate the CO poisoning for enhancing methanol oxidation electrocatalysis. By adjusting the amounts of YOx and MoOx decorated on the surface of ultrathin Pt NWs, the optimized 22% YOx/MoOx–Pt NWs achieve a high specific activity of 3.35 mA cm−2 and a mass activity of 2.10 A mgPt−1, as well as the enhanced stability. In situ Fourier transform infrared (FTIR) spectroscopy and CO stripping studies confirm the contribution of YOx and MoOx to anti‐CO poisoning ability of the NWs. Density functional theory (DFT) calculations further reveal that the surface Y and Mo atoms with oxidation states allow COOH* to bind the surface through both the carbon and oxygen atoms, which can lower the free energy barriers for the oxidation of CO* into COOH*. The optimal NWs also show the superior activities toward the electro‐oxidation of ethanol, ethylene glycol, and glycerol.