Shangfeng Du

A simple approach for PtNi–MWCNT hybrid nanostructures as high performance electrocatalysts for the oxygen reduction reaction

We report a simple one-pot synthesis of PtNi–MWCNT hybrid nanostructures as a high performance and durable electrocatalyst for the oxygen reduction reaction (ORR) in polymer electrolyte fuel cells (PEFCs). The whole approach was achieved in aqueous solution at room temperature, without using any organic solvents, templates or growth inducing catalysts. A single-crystal Pt nanoparticle was successfully grown on Ni nanoparticle surfaces using commercial Ni-coated MWCNTs as a support. PtNi–MWCNT hybrids possessed a high mass activity of 0.51 A mgPt−1, nearly double that of the state-of-the-art TKKs Pt/C catalyst. After an accelerated durability test by 2500 potential sweeping cycles, PtNi–MWCNTs still retained 89.6% of their initial mass activity, which is 0.46 A mgPt−1 and 4% higher than the DOE (Department of Energy) target of 0.44 A mgPt−1 for 2017–2020. The reported synergy between high performance and simple synthesis demonstrated that PtNi–MWCNTs could be effective cathode catalysts for high performance PEFCs.

A facile hydrothermal synthesis of MnO2 nanorod–reduced graphene oxide nanocomposites possessing excellent microwave absorption properties

Pure MnO2 nanorods and MnO2 nanorod/reduced graphene oxide (RGO) nanocomposites are prepared for microwave absorption by using a simple one-step hydrothermal method without using any toxic solvents. The results demonstrate that the MnO2 phases possess a high crystallization degree in both the pure nanorods and the nanocomposites but the nanocomposites exhibit two hybrid Mn phases, distinct from MnO2 in the pure nanorods. The electromagnetic characteristics and electromagnetic wave (EMW) absorption properties of the materials are investigated. The thickness dependent reflection loss shows that the peak frequency and effective absorption bandwidth all decrease with the increasing material thickness. Compared with the pure MnO2 nanorods, the introduction of RGO enhances the microwave absorbing intensity and effective absorption bandwidth. The maximum reflection loss value of the nanocomposites reaches −37 dB at 16.8 GHz with a thickness of 2.0 mm and the wide bandwidth corresponding to the reflection loss below −10 dB starts from 13 GHz until a value of −22 dB at 18 GHz. The enhanced microwave absorbing properties can be ascribed to the improved permittivity, dielectric loss and especially the synergistic effects between MnO2 nanorods and RGO nanosheets at their interfaces in the unique nanostructures of the MnO2/RGO nanocomposites.

Plasma nitriding induced growth of Pt-nanowire arrays as high performance electrocatalysts for fuel cells

In this work, we demonstrate an innovative approach, combing a novel active screen plasma (ASP) technique with green chemical synthesis, for a direct fabrication of uniform Pt nanowire arrays on large-area supports. The ASP treatment enables in-situ N-doping and surface modification to the support surface, significantly promoting the uniform growth of tiny Pt nuclei which directs the growth of ultrathin single-crystal Pt nanowire (2.5–3 nm in diameter) arrays, forming a three-dimensional (3D) nano-architecture. Pt nanowire arrays in-situ grown on the large-area gas diffusion layer (GDL) (5 cm2) can be directly used as the catalyst electrode in fuel cells. The unique design brings in an extremely thin electrocatalyst layer, facilitating the charge transfer and mass transfer properties, leading to over two times higher power density than the conventional Pt nanoparticle catalyst electrode in real fuel cell environment. Due to the similar challenges faced with other nanostructures and the high availability of ASP for other material surfaces, this work will provide valuable insights and guidance towards the development of other new nano-architectures for various practical applications.

Aggregation and adhesion of gold nanoparticles in phosphate buffered saline

In applications in medicine and more specifically drug delivery, the dispersion stability of nanoparticles plays a significant role on their final performances. In this study, with the use of two laser technologies, dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA), we report a simple method to estimate the stability of nanoparticles dispersed in phosphate buffered saline (PBS). Stability has two features: (1) self-aggregation as the particles tend to stick to each other; (2) disappearance of particles as they adhere to surrounding substrate surfaces such as glass, metal, or polymer. By investigating the effects of sonication treatment and surface modification by five types of surfactants, including nonylphenol ethoxylate (NP9), polyvinyl pyrrolidone (PVP), human serum albumin (HSA), sodium dodecyl sulfate (SDS) and citrate ions on the dispersion stability, the varying self-aggregation and adhesion of gold nanoparticles dispersed in PBS are demonstrated. The results showed that PVP effectively prevented aggregation, while HSA exhibited the best performance in avoiding the adhesion of gold nanoparticle in PBS onto glass and metal. The simple principle of this method makes it a high potential to be applied to other nanoparticles, including virus particles, used in dispersing and processing.

A new measure of molecular attractions between nanoparticles near kT adhesion energy.

The weak molecular attractions of nanoparticles are important because they drive self-assembly mechanisms, allow processing in dispersions e.g. of pigments, catalysts or device structures, influence disease through the attraction of viruses to cells and also cause potential toxic effects through nanoparticle interference with biomolecules and organs. The problem is to understand these small forces which pull nanoparticles into intimate contact; forces which are comparable with 3kT/2z the thermal impact force experienced by an average Brownian particle hitting a linear repulsive potential of range z. Here we describe a new method for measuring the atomic attractions of nanoparticles based on the observation of aggregates produced by these small forces. The method is based on the tracking of individual monosize nanoparticles whose diameter can be calculated from the Stokes-Einstein analysis of the tracks in aqueous suspensions. Then the doublet aggregates are distinguished because they move slower and are also very much brighter than the dispersed nanoparticles. By finding the ratio of doublets to singlets, the adhesive energy between the particles can be calculated from known statistical thermodynamic theory using assumptions about the shape of the interaction potential. In this way, very small adhesion energies of 2kT have been measured, smaller than those seen previously by atomic force microscopy (AFM) and scanning tunneling microscopy (STM).

Large-scale preparation of porous ultrathin Ga-doped ZnO nanoneedles from 3D basic zinc carbonate superstructures

A facile procedure for large-scale preparation of porous ZnO 1D nanomaterials with good electrical conductivity has been demonstrated for the first time. Porous ultrathin Ga-doped ZnO nanoneedles can be prepared by calcining the precursor of ultrathin Ga-doped basic zinc carbonate (BZC) nanoneedles obtained from BZC 3D superstructures, which are synthesized by a simple chemical co-precipitation method at room temperature, without using any catalyst, template or surfactant. There is evidence that the growth mechanisms of the BZC 3D superstructures and nanoneedles are correlated with the concentrations of ammonium ions and ethanol in the synthesis solution. The as-prepared porous Ga-doped ZnO nanoneedles have a thickness of only a couple of nanometers, consisting of many fine nanoparticles in a few nanometers. Electrical conductivity measurements indicate that porous ultrathin ZnO nanoneedles have a volume resistivity similar to that of the spherical Ga-doped ZnO nanoparticles. The porous nanostructures and good electrical conductivity make the porous ultrathin ZnO 1D nanoneedles promising candidates for applications in electrochemical fields.

In situ grown nanoscale platinum on carbon powder as catalyst layer in proton exchange membrane fuel cells (PEMFCs)

An extensive study has been conducted on the proton exchange membrane fuel cells (PEMFCs) with reducing Pt loading. This is commonly achieved by developing methods to increase the utilization of the platinum in the catalyst layer of the electrodes. In this paper, a novel process of the catalyst layers was introduced and investigated. A mixture of carbon powder and Nafion solution was sprayed on the glassy carbon electrode (GCE) to form a thin carbon layer. Then Pt particles were deposited on the surface by reducing hexachloroplatinic (IV) acid hexahydrate with methanoic acid. SEM images showed a continuous Pt gradient profile among the thickness direction of the catalytic layer by the novel method. The Pt nanowires grown are in the size of 3 nm (diameter)×10 nm (length) by high solution TEM image. The novel catalyst layer was characterized by cyclic voltammetry (CV) and scanning electron microscope (SEM) as compared with commercial Pt/C black and Pt catalyst layer obtained from sputtering. The results showed that the platinum nanoparticles deposited on the carbon powder were highly utilized as they directly faced the gas diffusion layer and offered easy access to reactants (oxygen or hydrogen).

Virus Concentration and Adhesion Measured by Laser Tracking

At present there are few methods available for observing the adhesion of viruses. Also, it is difficult to determine virus concentrations on-line. This paper describes the “NanoSight,” a microscope instrument which counts nanoparticles directly from scattered laser light and then determines their diameter by laser tracking the Brownian movement and applying the Stokes-Einstein theory to the random walk pathways. By applying this instrument to preparations of adenovirus, the concentration of viruses has been measured and compared with polystyrene latex spheres. Then, the instrument has been used to detect aggregates of viruses in the suspension. Taking the number of aggregates as a measure of the interparticle adhesion for equal spheres, the self-adhesion of the virus particles has been estimated as a function of two parameters, the adhesion energy and the range of the interaction. The results showed that the virus adhesion was similar to the self-adhesion of polystyrene.

Materials for Polymer Electrolyte Membrane Fuel Cells (PEMFCs): Electrolyte Membrane, Gas Diffusion Layers, and Bipolar Plates

This article explores the materials used in the components in the polymer electrolyte membrane fuel cell (PEMFC), namely; the polymer electrolyte membrane, the flow field plate, and the gas diffusion layer. Each section deals with one of the listed components considering: (a) its function within a PEMFC, (b) the material properties influencing its operation and performance, (c) the main materials discussed in the literature, and (d) the state-of-art and current research activity.