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The growth and breadth of nanoparticle (NP) research now encompasses many scientific and technologic fields, which has driven the want to control NP dimensions, structures and properties. Recent advances in NP synthesis, especially in solution phase synthesis, and characterization have made it possible to tune NP sizes and shapes to optimize NP properties for various applications. In this review, we summarize the general concepts of using solution phase chemistry to control NP nucleation and growth for the formation of monodisperse NPs with polyhedral, cubic, octahedral, rod, or wire shapes and complex multicomponent heterostructures. Using some representative examples, we demonstrate how to use these monodisperse NPs to tune and optimize NP catalysis of some important energy conversion reactions, such as the oxygen reduction reaction, electrochemical carbon dioxide reduction, and cascade dehydrogenation/hydrogenation for the formation of functional organic compounds under greener chemical reaction conditions. Monodisperse NPs with controlled surface chemistry, morphologies and magnetic properties also show great potential for use in biomedicine. We highlight how monodisperse iron oxide NPs are made biocompatible and target-specific for biomedical imaging, sensing and therapeutic applications. We intend to provide readers some concrete evidence that monodisperse NPs have been established to serve as successful model systems for understanding structure-property relationships at the nanoscale and further to show great potential for advanced nanotechnological applications.

Efficient electro‐oxidation of formic acid, methanol, and ethanol is challenging owing to the multiple chemical reaction steps required to accomplish full oxidation to CO2. Herein, a ternary CoPtAu nanoparticle catalyst system is reported in which Co and Pt form an intermetallic L10‐structure and Au segregates on the surface to alloy with Pt. The L10‐structure stabilizes Co and significantly enhances the catalysis of the PtAu surface towards electro‐oxidation of ethanol, methanol, and formic acid, with mass activities of 1.55 A/mgPt, 1.49 A/mgPt, and 11.97 A/mgPt, respectively in 0.1 m HClO4. The L10‐CoPtAu catalyst is also stable, with negligible degradation in mass activities and no obvious Co/Pt/Au composition changes after 10 000 potential cycles. The in situ surface‐enhanced infrared absorption spectroscopy study indicates that the ternary catalyst activates the C−C bond more efficiently for ethanol oxidation. [ABSTRACT FROM AUTHOR]

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 new chemical process is developed to prepare strongly ferromagnetic SmCo5 nanoparticles (NPs) via controlled reduction of SmCo‐O multipods. The 200 nm SmCo5 NPs embedded in polyethylene glycol are aligned magnetically and show the room temperature coercivity of 49.2 kOe. The synthetic method has also been extended to prepare ferromagnetic Sm2Co17 and Sm2Fe17N3 NPs. [ABSTRACT FROM AUTHOR]

We report in this article a detailed study on how to stabilize a first-row transition metal (M) in an intermetallic L10-MPt alloy nanoparticle (NP) structure and how to surround the L10-MPt with an atomic layer of Pt to enhance the electrocatalysis of Pt for oxygen reduction reaction (ORR) in fuel cell operation conditions. Using 8 nm FePt NPs as an example, we demonstrate that Fe can be stabilized more efficiently in a core/shell structured L10-FePt/ Pt with a 5 À Pt shell. The presence of Fe in the alloy core induces the desired compression of the thin Pt shell, especially the two atomic layers of Pt shell, further improving the ORR catalysis. This leads to much enhanced Pt catalysis for ORR in 0.1 M HClO4 solution (at both room temperature and 60 °C) and in the membrane electrode assembly (MEA) at 80 °C. The L10-FePt/Pt catalyst has a mass activity of 0.7 A/mgPt from the half-cell ORR test and shows no obvious mass activity loss after 30 000 potential cycles between 0.6 and 0.95 V at 80 °C in the MEA, meeting the DOE 2020 target (<40% loss in mass activity). We are extending the concept and preparing other L10-MPt/Pt NPs, such as L10-CoPt/Pt NPs, with reduced NP size as a highly efficient ORR catalyst for automotive fuel cell applications. [ABSTRACT FROM AUTHOR]

We report a facile method for assembly of a monolayer array of nitrogen-doped graphene (NG) and nanoparticles (NPs) and the subsequent transfer of two layers onto a solid substrate (S). Using 3 nm NiPd NPs as an example, we demonstrate that NiPd-NG-Si (Si=silicon wafer) can function as a catalyst and show maximum NiPd catalysis for the hydrolysis of ammonia borane (H3NBH3, AB) with a turnover frequency (TOF) of 4896.8 h−1 and an activation energy ( Ea) of 18.8 kJ mol−1. The NiPd-NG-S catalyst is also highly active for catalyzing the transfer hydrogenation from AB to nitro compounds, leading to the green synthesis of quinazolines in water. Our assembly method can be extended to other graphene and NP catalyst materials, providing a new 2D NP catalyst platform for catalyzing multiple reactions in one pot with maximum efficiency. [ABSTRACT FROM AUTHOR]

Selective hydrogenation of cinnamaldehyde (CAL) to cinnamyl alcohol (COL) was conducted over a series of FeO x -doped Pt catalysts supported on a 15 wt% Al 2 O 3 @SBA-15 composite (15AS). It was found that the addition of FeO x to the catalyst greatly improved its performance. With an optimal Fe/Pt molar ratio of 0.25, the PtFe 0.25 /15AS catalyst reached a maximum reaction rate (defined as moles of converted CAL per gram of Pt per hour) of 13.93 mol g Pt −1 h −1 with 76.9% selectivity to COL. Additionally, the PtFe 0.25 /15AS catalyst afforded the highest TOF value (defined as moles of converted CAL per mole of Pt active sites per second) of 1.54 s −1 . X-ray photoelectron spectroscopy analyses and H 2 temperature-programmed reduction and CO diffuse-reflectance infrared Fourier-transformation spectroscopy studies reveal that there is strong interaction between Pt nanoparticles and Al 2 O 3 @SBA-15 composites and also between Pt and FeO x , resulting in Pt species with a positive charge being dominant in PtFe 0.25 /15AS catalysts. Therefore, Pt species with positive charges, together with FeO x species, are beneficial for preferential adsorption and activation of carbonyl bonds of CAL, so that the activity and selectivity to COL were improved by PtFe x /15AS catalysts ( x represents the Fe/Pt molar ratio). [ABSTRACT FROM AUTHOR]

Abstract: Impregnating hygroscopic nanoparticles, typically silica in Nafion membrane has received intense interest in high-temperature PEMFCs application due to increased water retention ability, proton conductivity and mechanical stability. However, typical Nafion/silica membranes may suffer from potential durability degradation because of the instability of inorganic–organic electrostatic interface under humidifying conditions. Here, we investigate microstructural evolutions of this membrane and the subsequent performance. Aggregation and dissolving of silica nanoparticles and membrane fractures are observed under humidifying and RH cycling tests, thus leading to a significant decay of proton conductivities from ∼0.095 S cm−1 to ∼0.055 S cm−1 after 720 h of RH cycles. Simultaneously, H2 crossover soars to nearly 40 times larger than the initial. Inorganic–organic interfaces are recognized to be crucial in the stability and performance of this type of composite membrane. The insight into the degradation process will provide meaningful reference for optimizing composite membranes and designing competent candidates for high-temperature PEMFCs operation. [Copyright &y& Elsevier]