Yanyun Ma

Facile synthesis of graphene/metal nanoparticle composites via self-catalysis reduction at room temperature.

Graphene/metal nanoparticle (NP) composites have attracted great interest for various applications as catalysts, electrodes, sensors, etc., due to their unique structures and extraordinary properties. A facile synthesis of graphene/metal NP composites with good control of size and morphology of metal NPs is critical to the practical applications. A simple method to synthesize graphene/metal NPs under a controllable manner via a self-catalysis reduction at room temperature has been developed in this paper. At first, metal NPs with desirable size and morphology were decorated on GO and then used as catalyst to accelerate the hydrolysis reaction of NaBH4 to reduce the graphene oxide. Compared to the existing methods, the method reported here features several advantages in which graphene/metal NPs are prepared without using toxic and explosive reductant, such as hydrazine or its derivatives, making it environmentally benign, and the reaction can be processed at room temperature with high efficiency and in a large range of pH values. The approach has been demonstrated to successfully synthesize graphene composites with various metal NPs in large quantity, which opens up a novel and simple way to prepare large-scale graphene/metal or graphene/metal oxide composites under mild conditions for practical applications. For example, graphene/AuNP composites synthesized by the method show excellent catalytic capability.

Facile fabrication of a well-ordered porous Cu-doped SnO2 thin film for H2S sensing.

Well-ordered Cu-doped and undoped SnO2 porous thin films with large specific surface areas have been fabricated on a desired substrate using a self-assembled soft template combined with simple physical cosputtering deposition. The Cu-doped SnO2 porous film gas sensor shows a significant enhancement in its sensing performance, including a high sensitivity, selectivity, and a fast response and recovery time. The sensitivity of the Cu-doped SnO2 porous sensor is 1 order of magnitude higher than that of the undoped SnO2 sensor, with average response and recovery times to 100 ppm of H2S of ∼ 10.1 and ∼ 42.4 s, respectively, at the optimal operating temperature of 180 °C. The well-defined porous sensors fabricated by the method also exhibit high reproducibility because of the accurately controlled fabrication process. The facile process can be easily extended to the fabrication of other semiconductor oxide gas sensors with easy doping and multilayer porous nanostructure for practical sensing applications.

Aqueous Solution Synthesis of Pt–M (M = Fe, Co, Ni) Bimetallic Nanoparticles and Their Catalysis for the Hydrolytic Dehydrogenation of Ammonia Borane

Platinum-based bimetallic nanocatalysts have attracted much attention due to their high-efficiency catalytic performance in energy-related applications such as fuel cell and hydrogen storage, for example, the hydrolytic dehydrogenation of ammonia borane (AB). In this work, a simple and green method has been demonstrated to successfully prepare Pt-M (M = Fe, Co, Ni) NPs with tunable composition (nominal Pt/M atomic ratios of 4:1, 1:1, and 1:4) in aqueous solution under mild conditions. All Pt-M NPs with a small size of 3-5 nm show a Pt fcc structure, suggesting the bimetallic formation (alloy and/or partial core-shell), examined by transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray absorption fine structure (XAFS) analysis. The catalytic activities of Pt-M NPs in the hydrolytic dehydrogenation of AB reveal that Pt-Ni NPs with a ratio of 4:1 show the best catalytic activity and even better than that of pure Pt NPs when normalized to Pt molar amount. The Ni oxidation state in Pt-Ni NPs has been suggested to be responsible for the corresponding catalytic activity for hydrolytic dehydrogenation of AB by XAFS study. This strategy for the synthesis of Pt-M NPs is simple and environmentally benign in aqueous solution with the potential for scale-up preparation and the in situ catalytic reaction.

Hollow NiFe2O4 nanospheres on carbon nanorods as a highly efficient anode material for lithium ion batteries

The integration of both hollow structure engineering and hybridization to design a novel composite consisting of metal oxides with carbon is highly promising for the anode of lithium ion batteries (LIBs) with high rate capability, remarkable stability, good safety and low cost. In this work, a unique hierarchical structure of NiFe2O4 nanospheres anchored on amorphous carbon nanorods (denoted as NiFe2O4 NSs@CNR) has been synthesized as an anode material for LIBs by using a metal organic framework (MOF) (Fe2Ni MIL-88) as the template and precursor without the addition of external carbon. Combining the hollow structure of NiFe2O4 nanospheres with the carbon nanorod matrix, the as-prepared NiFe2O4 NSs@CNR thus exhibits a superior electrochemical performance, which stabilized at an average capacity of 1355 mA h g−1 after 100 cycles at 0.1C and 1045.6 mA h g−1 after 400 cycles at 1C when evaluated as an anode material for LIBs. More importantly, the hollow NiFe2O4 NSs@CNR shows a long life-span capacity of 513.7 mA h g−1 even at a high rate of 2C after 1000 cycles.

Sn nanoparticles@nitrogen-doped carbon nanofiber composites as high-performance anodes for sodium-ion batteries

Recently, sodium-ion batteries (SIBs) have attracted increasing attention as an important supplement or alternative to lithium ion batteries (LIBs) due to the abundance of sodium resources and its much lower cost. A critical issue and great challenge in current battery research for the extensive application of SIBs is the development of earth-abundant and high-performance electrode materials. In various studies of these electrode materials, Sn-based nanocomposites have been identified as promising anodes for SIBs. In this study, Sn nanoparticles on nitrogen-doped carbon nanofiber composites (Sn@NCNFs) have been synthesized by an electrostatic spinning technique and used as anodes for SIBs. Morphological and structural characterizations indicate that the Sn nanoparticles adhere uniformly on the surface of the nitrogen-doped carbon nanofibers. The corresponding specific capacity can reach over 600 mA h g−1 at 0.1C after 200 cycles. Additionally, these Sn@NCNFs also show excellent high-rate cycling performance and can maintain a capacity of up to 390 mA h g−1 even at an extremely high rate of 1C for over 1000 cycles. The results demonstrate that this Sn@NCNFs composite is a promising anode material with good reversible capacity and cycling performance for SIBs.

Carbon coated bimetallic sulfide nanodots/carbon nanorod heterostructure enabling long-life lithium-ion batteries

Exploitation of high capacity and long-life anode materials is essential for the development of lithium-ion batteries (LIBs) with high energy density. Metal sulfides have shown great potential as anode materials for LIBs due to their high theoretical specific capacity and excellent electronic properties and therefore they are considered as excellent candidates for anode materials. However, structural degradation during cycling and polysulfide dissolution has limited their practical application. In this work, we design a unique 0D/1D heterostructure of carbon coated iron–nickel sulfide nanodots/carbon nanorod through simultaneous decomposition and sulfidation of a bi-metal organic framework template. The resultant nanodots/nanorod heterostructure allows for fast ion/electron transport kinetics, suppresses polysulfide dissolution and ensures structural integrity during the lithiation/delithiation process. Consequently, this carbon coated iron–nickel sulfide nanodots/carbon nanorod structure exhibits a high specific capacity (851.3 mA h g−1 at 0.5C after 200 cycles) and an excellent cycling stability (484.7 mA h g−1 after 1000 cycles at a high rate of 4C).

PtxNi10−xO nanoparticles supported on N-doped graphene oxide with a synergetic effect for highly efficient hydrolysis of ammonia borane

Oxidized Pt–Ni nanoparticles were deposited on N-doped graphene oxide (NGO) for the hydrolysis of ammonia borane (AB). The optimized Pt3Ni7O–NGO sample shows a high total turnover frequency (TOF) value of 709.6 mol H2 per mol Cat-Pt per min in the hydrolysis of AB, which is one of the best values for Pt-based catalysts to date. Moreover, when calculating all metal contents (mainly Ni, Pt : Ni = 1 : 5) in the hybrid, the total TOF value is still as high as 120.7 mol H2 per mol Cat-metal per min, better than that of pure Pt/C or Pt on NGO. The hybrid also exhibits a good stability with more than 76% activity (TOF = 544.9) after 9 cycles. Synchrotron radiation X-ray absorption spectroscopy reveals that Pt and Ni in the catalyst exhibit a strong interaction through oxygen bonds and the bimetallic structure shows further interaction with the support material. All the components in the hybrid can thus be connected to show a synergetic effect for enhanced catalytic performance. The excellent performance can be related to the unique electronic structure of the hybrid with the synergetic effect, which may also shed light on the design of high-efficiency catalysts for other energy-related applications.