Zabeada Aslam

Facile, fast, and inexpensive synthesis of monodisperse amorphous nickel-phosphide nanoparticles of predefined size.

Monodisperse, size-controlled Ni-P nanoparticles were synthesised in a single step process using triphenyl-phosphane (TPP), oleylamine (OA), and Ni(II)acetyl-acetonate. The nanoparticles were amorphous, contained ~30 at% P and their size was controlled between 7-21 nm simply by varying the amount of TPP. They are catalytically active for tailored carbon nanotube growth.

Study of FePt deposited reduced graphene oxide's utility as a catalyst towards oxygen reduction and methanol oxidation reactions

Hydrogen and methanol fuelled polymer electrolyte fuel cells (PEFC) penetration in the commercial market is slowed by the use of expensive Pt and PtRu as electrocatalysts. Transition metal based Pt alloy catalysts have historically struggled for durability in acidic environments. Reduced graphene oxide (RGO) supported Pt alloy catalysts have gained significant interest recently due to improvements in catalyst–support interaction that lead to better durability and performance. In this report we investigate the performance and durability aspects of FePt supported on RGO towards oxygen reduction and methanol oxidation reactions. PXRD and TEM results show that the FePt nanoparticle size is in the range of 4–7 nm and TGA measurements show that the metal loading of the catalyst is ∼55%. Electrochemical measurements towards ORR reveal a significant improvement in activity and durability for FePtGO over commercial PtC and FePtC. The utilization of RGO as a support certainly increases the lifetime of transition metal–Pt alloys that are generally susceptible to durability issues under acidic environments in fuel cells.

Electronic property investigations of single-walled carbon nanotube bundles in situ within a transmission electron microscope: an evaluation

We have evaluated a combined transmission electron microscopy (TEM)–scanning tunnelling microscopy (STM) (hence TEM‐STM) sample holder for the investigation of the mechanical and electrical properties of individual bundles of single‐walled carbon nanotubes (SWCNTs) together with their simultaneous observation, analysis and mechanical modification in the TEM. Current‐voltage (I–V) measurements from bundles of SWCNTs were observed to change as the bundles were deformed both reversibly and irreversibly, although the observed behaviour was somewhat complex. Electron energy loss spectroscopy (EELS) analysis revealed measurable changes in the bonding of the carbon atoms within the graphene layers upon bundle deformation, with measurable changes in the π*/(π*+σ*) peak ratios observed at the carbon K‐edge. Reversible deformation of the bundles was consistent with the sensitivity of σ bonding to deviations from nonplanarity, whereas irreversible deformation was consistent with the introduction of nonhexagonal defects into the graphene sheets.

Fe–N-Doped Mesoporous Carbon with Dual Active Sites Loaded on Reduced Graphene Oxides for Efficient Oxygen Reduction Catalysts

Transition metal/nitrogen/carbon (M-N/C) catalysts are considered as one of the most promising candidates to replace Pt/C catalysts for oxygen reduction reactions (ORRs). Here, we have designed novel reduced graphene oxide (rGO)-supported Fe-N-doped carbon (Fe-N-C/rGO) catalysts via simple pyrolysis of polypyrrole (Ppy)-FeO-GO composites. The as-prepared catalysts induced an onset potential of 0.94 V and a half-wave potential of 0.81 V in alkaline solutions, which is much better than those of the counterpart N-C and N-C/rGO catalysts and comparable to that of Pt/C catalysts. Moreover, the Fe-N-C/rGO catalysts showed improved durability and higher tolerance against methanol crossover than Pt/C in alkaline solutions. This superior ORR performance can be ascribed to the combined catalytic effect of both Fe-based nanoparticles (Fe3O4, Fe4C) and Fe-Nx sites, as well as fast mass transfer and accessible active sites benefiting from the mesoporous structure and high specific surface area. This work provides new insight for synthesis of a more promising nonplatinum electrocatalyst for metal-air batteries and fuel-cell applications.

Customised transition metal oxide nanoparticles for the controlled production of carbon nanostructures

Monodisperse magnetite (Fe3O4) and cobaltous oxide (CoO) nanoparticles were synthesised using a fast (up to 50 times quicker than previously reported) and facile one-pot, one-step reaction. The Fe3O4 nanoparticles had a constant size between 5 to 7 nm independent of the reagents used. Size controlled cube shaped CoO particles in the range of 10–20 nm were formed and it was possible to create voids in these particles in a controlled way. Carbon nanotubes were grown on these catalyst particles and their structures were compared. Structures of the nanotubes differed between straight, bamboo-like or partly coiled depending on the nanoparticle system used, suggesting the possibility of selection of these structures.

Supported Catalytic Growth of SWCNTs using the CVD Method

The growth of carbon nanotubes (CNTs) from supported metal catalysts using the CVD method with CH4 as the carbon feedstock was investigated using SEM and TEM. Studies include the influence of the substrate structure, the metal catalyst content and other experimental parameters on the nature of the CNTs produced using calcined aluminium nitrate and delta-alumina nanoparticles (~13nm). The iron catalyst precursors are ferric sulphate and also iron oxide nanoparticles. Using an aberration corrected STEM and a FEGTEM BF imaging has been used to identify symmetries of tubes produced, as well as a TEM-STM tip to measure I-V curves of SWCNTs. It appears the optimum iron precursor and catalyst support for production of SWCNTs is either ferric sulphate or iron oxide nanoparticles supported on deltaalumina nanoparticles.

Initial Studies Using a Combined TEM - Scanning Tunnelling Microscopy (STM) Side Entry Sample Holder

A combined TEM-STM holder has been evaluated and the STM tip has been used to investigate the mechanical and electrical properties of individual carbon nanotubes with simultaneous observation and analysis in the TEM.

A facile route to self-assembled Hg//MoSI nanowire networks

Nanotechnology crucially depends on new molecular-scale materials with tunable properties. In molecular electronics, building blocks have been reduced to single molecules, while connectors have largely remained at the mesoscopic scale. As a result, the behaviour of such devices is largely governed by interface effects and hence, currently, attention is focused on finding suitable molecular-scale alternatives. In this paper we discuss a new generation of one-dimensional inorganic nanostructures aimed at to replacing the mesoscopic connectors currently used in the electronics industry. We demonstrate how chemical functionalisation of nanowires consisting of molybdenum, sulphur and iodine in conjunction with very low concentrations of molecular mercury leads to one-dimensional systems which can be easily connected opening up new pathways to controlled deposition and interface formation.

Processing and Aberration-Corrected Imaging of Novel Low-Dimensional Nanostructures

Low-dimensional nanostructured materials such as organic and inorganic nanotubes [1], nanowires [2] and platelets [3] are potentially useful in a number of areas of nanoscience and nanotechnology due to their remarkable mechanical, electrical and thermal properties [4]. However difficulties associated with their lack of processability have seriously hampered both. In the last few years dispersion and exfoliation methods have been developed and demonstrated to apply universally to 1D and 2D nanostructures of very diverse nature [3,5], offering a practical means of processing the nanostructures for a wide range of innovative technologies. To make real applications truly feasible, however, it is crucial to fully characterize the nanostructures on the atomic scale and correlate this information with their physical and chemical properties. Advances in aberration-corrected optics in electron microscopy have revolutionised the way to characterise nano-materials, opening new frontiers for materials science. With the recent advances in nanostructure processability, electron microscopes are now revealing the structure of the individual components of nanomaterials, atom by atom. Here we will present an overview of very different low-dimensional materials issues, showing what aberration-corrected electron microscopy can do for materials scientists. Among the first materials to have benefitted most from these advances are the inorganic nanowires made up from molybdenum, sulfur and iodine (MoSI nanowires). Purification and dispersion in liquid phase media and exfoliation of the as-synthesized ropes down to single, sub-nanometer wide wires or very thin nano-sized bundles has allowed us to study their previously unknown atomic structure [6-7]. Innovative nanowire functionalisation routes are also studied. Leading edge subangstrom resolution electron microscopy techniques, combining aberration corrected High Resolution Transmission Electron Microscopy (HRTEM) and Scanning Transmission Electron Microscopy (STEM) are here applied to obtain crucial structure-properties correlations.

Growth of Carbon Nanotubes from Supported Metal Catalysts

The growth of carbon nanotubes (CNTs) from supported metal catalysts is under investigation using the chemical vapour deposition (CVD) method with CH4 as the carbon feedstock. Studies include the effects of the structure of the support media, metal catalyst content and other experimental parameters on the CNTs produced. The effects of the surface structure on the catalyst particles and the CNTs produced are being investigated using various alumina-based supported iron catalysts. Supported catalysts have been prepared from ferric sulphate and either aluminium nitrate or deltaalumina nanoparticles in order to produce different substrate morphologies. Preliminary TEM studies indicate that under the same experimental conditions Fe supported on alumina nanoparticles produces mostly bundles of DWCNTs, whereas Fe supported on alumina derived from aluminium nitrate produces predominantly SWNCT bundles with some MWCNTs. The effects of catalyst content on the CNT production is also being investigated with Fe content varying between 5% and 30%. Preliminary TEM results show the presence of bundles of SWCNTs for all the Fe contents except 5% Fe; no CNTs have been observed in this sample.