Yongsheng Yu

A New Core/Shell NiAu/Au Nanoparticle Catalyst with Pt-like Activity for Hydrogen Evolution Reaction.

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.

Monodisperse MPt (M = Fe, Co, Ni, Cu, Zn) Nanoparticles Prepared from a Facile Oleylamine Reduction of Metal Salts

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.

One-Pot Synthesis of Urchin-like FePd–Fe3O4 and Their Conversion into Exchange-Coupled L10–FePd–Fe Nanocomposite Magnets

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.

Controlled Anisotropic Growth of Co‐Fe‐P from Co‐Fe‐O Nanoparticles

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.

Cobalt‐Substituted Magnetite Nanoparticles and Their Assembly into Ferrimagnetic Nanoparticle Arrays

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.

From FePt-Fe3O4 to L10-FePt-Fe nanocomposite magnets with a gradient interface

We report a novel approach for the fabrication of exchange-coupling L10-FePt–bcc-Fe nanocomposites with a gradient interface between hard and soft phases from FePt nanoparticles (NPs) and FePt–Fe3O4 dumbbell shaped NPs, which are prepared by a facile one-pot synthesis method. High temperature annealing in argon is first used to convert FePt in FePt–Fe3O4 dumbbell shaped NPs to the L10-FePt phase. Then Fe3O4 in FePt–Fe3O4 dumbbell shaped NPs is reduced to bcc-Fe by low temperature annealing in reducing gas, forming L10-FePt–Fe nanocomposites. The L10-FePt–Fe nanocomposites exhibit both large coercivity and high magnetic moment. The work demonstrates that creating a nanoscale gradient interface between magnetically hard and soft phases is a promising approach for the fabrication of high performance permanent magnets.

Interstitial-nitrogen effect on phase transition and magnetocaloric effect in Mn(As,Si) (invited)

The effect of interstitial nitrogen on the phase transition and magnetocaloric behavior of MnAs1−xSixNδ (x=0.03, 0.06, and 0.09) is investigated. The interstitial nitrogen atoms cause the step-scanned x-ray diffraction peaks to shift toward lower angles and lower the Curie temperature, whereas silicon addition increases the Curie temperature to near room temperature. The thermal hysteresis is reduced to nearly 0 in MnAs1−xSixNδ, which is beneficial to practical applications. For a field change of 5 T, the largest magnetic entropy change and refrigerant capacity are 14.6 J kg−1 K−1 at 247 K and 360 J kg−1, which is slightly higher than the entropy change in the parent alloy. Finally, we briefly discuss the occurrence and origin of the “virgin effect” in MnAs.

Effects of total thickness on (001) texture, surface morphology, and magnetic properties of [Fe/Pt]n multilayer films by monatomic layer deposition

Atomic-scale [Fe/Pt]n multilayer films with different total thickness were prepared on thermally oxidized Si (100) substrates at room temperature by monatomic layer deposition using dc-magnetron and rf-magnetron sputtering. Effects of the total thickness on (001) texture, surface morphology, and magnetic properties of the postannealed films have been investigated. It is found that the particlelike structure films with perfect (001) texture and perpendicular magnetic anisotropy are obtained with a thickness of less than or equal to 6.5 nm. After 500 °C annealing, the films with thickness of 6.5 and 11.9 nm show very smooth surface. In addition, with increasing total thickness of the films, (001) texture and perpendicular magnetic anisotropy of the annealed films deteriorate, and the films become continuous in structure. The total thickness of the films also affects the exchange-coupling interaction among FePt magnetic grains and the magnetization reversal process.

Bifunctional networked Ag/AgPd core/shell nanowires for the highly efficient dehydrogenation of formic acid and subsequent reduction of nitrate and nitrite in water

Nitrate (NO3−) and nitrite (NO2−) pollution in water has increasingly become a serious environmental concern. The catalytic reduction of NO3− and NO2− to harmless N2 by a reducing agent is considered to be one of the most promising methods to remove NO3− and NO2− from water. Herein, we report the one-pot synthesis of networked Ag/AgPd core/shell nanowires (CS-NWs) via seed-mediated growth in polyol solution. The shell thickness of the networked Ag/AgPd CS-NWs can be readily controlled by tuning the amount of precursors. The networked Ag/AgPd CS-NWs with a 0.9 nm shell thickness exhibited the highest activity towards the dehydrogenation catalysis of FA with an initial TOF of 1400 h−1 at 50 °C, and the highest selectivity for the catalysis of NO3− and NO2− to N2 in water and at room temperature. Their enhanced bifunctional catalytic performance could be attributed to more efficient electron transfer from PVPI and Ag to Pd. This work demonstrates a new way to prepare bifunctional nanocatalysts for the removal of NO3− and NO2− from water using FA as the in situ hydrogen source.

Hierarchical mesoporous Co 3 O 4 @ZnCo 2 O 4 hybrid nanowire arrays supported on Ni foam for high-performance asymmetric supercapacitors

In this paper, hierarchical mesoporous Co3O4@ZnCo2O4 hybrid nanowire arrays (NWAs) on Ni foam were prepared through a two-step hydrothermal process associated with successive annealing treatment. The Co3O4@ZnCo2O4 hybrid NWAs exhibited excellent electrochemical performances with a high specific capacity of 1240.5 C g−1 at a current density of 2 mA cm−2, with rate capability of 59.0% shifting from 2 to 30 mA cm−2, and only a 9.1% loss of its capacity even after 3,000 cycles at a consistent current density of 10 mA cm−2. An asymmetric supercapacitor (Co3O4@ZnCo2O4 NWAs||activated carbon) was fabricated and exhibited a high specific capacity of 168 C g−1 at a current density of 1 A g−1. And a preferable energy density of 37.3Wh kg−1 at a power density of 800 W kg−1 was obtained. The excellent electrochemical performances indicate the promising potential application of the hierarchical mesoporous Co3O4@ZnCo2O4 hybrid NWAs in energy storage field.摘要本文采用两步水热法和连续的退火处理过程, 制备了分层介孔Co3O4@ZnCo2O4复合纳米线阵列. 所制备的Co3O4@ZnCo2O4复合纳米线阵列具有优异的电化学性能, 在2 mA cm−2的电流密度下具有高达1240.5 C g−1的比容量. 当电流密度升高至30 mA cm−2时, 比容量保持率为59.0%, 甚至在10 mA cm−2的电流密度下循环3000圈, 比容量仅下降9.1%. 将其与活性炭组装成非对称超级电容器, 可以在1 A g−1的电流密度下表现出168 C g−1的比容量. 当功率密度为800 W kg−1时, 能量密度为37.3 W h kg−1. Co3O4@ZnCo2O4复合纳米阵列在储能领域具有广阔的应用前景.