Md. Shahriar A. Hossain

Carbohydrate doping to enhance electromagnetic properties of MgB2 superconductors

The effect of carbohydrate doping on lattice parameters, microstructure, Tc, Jc, Hirr, and Hc2 of MgB2 has been studied. In this work the authors used malic acid as an example of carbohydrates as an additive to MgB2. The advantages of carbohydrate doping include homogeneous mixing of precursor powders, avoidance of expansive nanoadditives, production of highly reactive C, and significant enhancement in Jc, Hirr, and Hc2 of MgB2, compared to undoped samples. The Jc for MgB2+30wt% C4H6O5 sample was increased by a factor of 21 at 5K and 8T without degradation of self-field Jc.

The enhanced Jc and Birr of in situ MgB2 wires and tapes alloyed with C4H6O5 (malic acid) after cold high pressure densification

Cold high pressure densification, a method recently introduced at GAP in Geneva, was applied for improving the transport critical current density, Jc, and the irreversibility field, Birr, of monofilamentary in?situ?MgB2 wires and tapes alloyed with 10?wt%?C4H6O5 (malic acid). Tapes densified at 1.48?GPa exhibited after reaction an enhancement of Jc from 2 to 4 ? 104?A?cm?2 at 4.2?K/10?T and from 0.5 to 4 ? 104?A?cm?2 at 20?K/5?T, while the Birr was enhanced from 19.3 to 22?T at 4.2?K and from 7.5 to 10.0?T at 20?K. Cold densification also caused a strong enhancement of B(104), the field at which Jc takes the value 1 ? 104?A?cm?2. For tapes subjected to 1.48?GPa, and at 4.2?K were found to increase from 11.8 and 10.5?T to 13.2 and 12.2?T, respectively. Almost isotropic conditions were obtained for rectangular wires with aspect ratios a/b<2 subjected to 2.0?GPa, where and ?T were obtained. At 20?K, the wires exhibited an almost isotropic behavior, with ?T and ?T, Birr(20?K) being ~10?T. These values are equal to or higher than the highest values reported so far for isotropic in?situ wires with SiC or other carbon based additives. Further improvements are expected on optimizing the cold high pressure densification process, which has the potential for fabrication of MgB2 wires of industrial lengths.

Strong enhancement of Jc and Birr in binary in?situ?MgB2 wires after cold high pressure densification

Cold high pressure densification was found to substantially enhance the critical current density of binary in situ Fe/MgB2 wires. A wire densified at 1.85 GPa exhibited at 20 K and 5 T an increase of Jc by 300% with respect to same wire without the application of pressure. At 4.2 K and 10 T, Jc was found to be increased by 53%. The decrease of the electrical resistance for densified wires reflects an improved connectivity. The values of Birr at 4.2 and 20 K were enhanced up to 0.7 T for densified wires. After applying pressures up to 6.5 GPa at 300 K, the relative mass density dm of the unreacted (B+Mg) mixture inside the filament increased up to 96% of the theoretical density. This corresponds to a relative mass density df in the reacted MgB2 filaments of 73%. A quantitative correlation between filament mass density and critical current density was established.

Strong enhancement of Jc in binary and alloyed in-situ MgB2 wires by a new approach: Cold high pressure densification

Cold high pressure densification was found to substantially enhance the critical current density of binary in situ Fe/MgB2 wires. A wire densified at 1.85 GPa exhibited at 20 K and 5 T an increase of Jc by 300% with respect to same wire without the application of pressure. At 4.2 K and 10 T, Jc was found to be increased by 53%. The decrease of the electrical resistance for densified wires reflects an improved connectivity. The values of Birr at 4.2 and 20 K were enhanced up to 0.7 T for densified wires. After applying pressures up to 6.5 GPa at 300 K, the relative mass density dm of the unreacted (B+Mg) mixture inside the filament increased up to 96% of the theoretical density. This corresponds to a relative mass density df in the reacted MgB2 filaments of 73%. A quantitative correlation between filament mass density and critical current density was established.

Nanoarchitecture of MOF-derived nanoporous functional composites for hybrid supercapacitors

A new nanoarchitecture approach based on metal–organic frameworks (MOF) is reported that can achieve high electrochemical energy storage via utilizing both electric double-layer supercapacitive and pseudocapacitive properties within a single nanoporous composite particle. Herein, a predesigned Co2+-excess bimetallic hybrid Co/Zn zeolitic imidazole framework was used to fabricate a composite containing N-doped nanoporous carbon with a rich carbon nanotube (CNT) content on particle surfaces without H2, with the carbon coexisting with Co nanoparticles (NPs) and Co3O4, through controlled carbonization at 800 °C and subsequent oxidation at 250–300 °C. Optimized nanoporous carbon composites were obtained by tracking the formation of Co3O4 and destruction of N-doped nanoporous carbon (NPC) via detailed X-ray diffraction and X-ray photoelectron spectroscopy analysis. The resulting material showed a high surface area of ∼202 m2 g−1 and included coexisting micro- and mesoporous N-doped carbon, CNTs, Co NPs, and Co3O4 (15 nm in size) after a thermal oxidation process in air at 250 °C for 5 h. Surprisingly, the as-prepared MOF-derived nanoarchitecture exhibited superior electrochemical storage performance, with a capacitance of 545 F g−1 within a wide potential window, achieving up to 320% enhanced capacitance compared to that of pristine nanoporous carbon, which is higher than those of most MOF-derived carbons reported so far. Our strategic nanoarchitecture design for MOFs offers a new opportunity for future applications in high performance energy storage systems.

Strategies for Improving the Functionality of Zeolitic Imidazolate Frameworks: Tailoring Nanoarchitectures for Functional Applications

Zeolitic imidazolate frameworks (ZIFs), a subclass of metal-organic frameworks (MOFs) built with tetrahedral metal ions and imidazolates, offer permanent porosity and high thermal and chemical stabilities. While ZIFs possess some attractive physical and chemical properties, it remains important to enhance their functionality for practical application. Here, an overview of the extensive strategies which have been developed to improve the functionality of ZIFs is provided, including linker modifications, functional hybridization of ZIFs via the encapsulation of guest species (such as metal and metal oxide nanoparticles and biomolecules) into ZIFs, and hybridization with polymeric matrices to form mixed matrix membranes for industrial gas and liquid separations. Furthermore, the developed strategies for achieving size and shape control of ZIF nanocrystals are considered, which are important for optimizing the textural characteristics as well as the functional performance of ZIFs and their derived materials/hybrids. Moreover, the recent trends of using ZIFs as templates for the derivation of nanoporous hybrid materials, including carbon/metal, carbon/oxide, carbon/sulfide, and carbon/phosphide hybrids, are discussed. Finally, some perspectives on the potential future research directions and applications for ZIFs and ZIF-derived materials are offered.

3D network of cellulose-based energy storage devices and related emerging applications

There has recently been a major thrust toward advanced research in the area of hierarchical carbon nanostructured electrodes derived from cellulosic resources, such as cellulose nanofibers (CNFs), which are accessible from natural cellulose and bacterial cellulose (BC). This research is providing a firm scientific basis for recognizing the inherent mechanical and electrochemical properties of those composite carbon materials that are suitable for carbon-electrode applications, where they represent obvious alternatives to replace the current monopoly of carbon materials (carbon nanotubes, reduced graphene oxide, and their derivatives). Significant promising developments in this area are strengthened by the one dimensional (1D) nanostructures and excellent hydrophobicity of the CNFs, the interconnected pore networks of carbon aerogels, and the biodegradable and flexible nature of cellulose paper and graphenic fibers. Outstanding electrode materials with different dimensions (1D, 3D) are derivable by the strategic choice of cellulose sources. This development requires special attention in terms of understanding the significant impact of the cellulose morphology on the final electrochemical performance. This review article attempts to emphasize the role of the different structural forms and corresponding composites derived from different forms of cellulose, including bacterial cellulose and its varied 3D nanostructures. This article strongly highlights that cellulose deserves special attention as an extremely abundant and extensively recyclable material that can serve as a source of components for electronic and energy devices. Along with emphasizing current trends in electrochemical device components from cellulose, we address a few emerging areas that may lead in future such as enzyme immobilization, flexible electronics, modelling of cellulosic microfibrils. Finally, we have discussed some of the important future prospects for cellulose as source of materials for future.

Enhancement of the in-field Jc of MgB2 via SiCl4 doping

In this work, we present the following important results: 1) We introduce a new Si source, liquid SiCl4, which is free of C, to significantly enhance the irreversibility field (Hirr), the upper critical field (Hc2), and the critical current density (Jc), with little reduction in the critical temperature (Tc). 2) Although Si can not incorporate into the crystal lattice, we found a reduction in the a-axis lattice parameter, to the same extent as for carbon doping. 3) The SiCl4 treated MgB2 shows much higher Jc with superior field dependence above 20 K than undoepd MgB2 and MgB2 doped with various carbon sources. 3) We provide an alternative interpretation for the reduction of the a lattice parameter in C- and non-C doped MgB2. 4). We introduce a new parameter, RHH (Hc2/Hirr), which can clearly reflect the degree of flux pinning enhancement, providing us with guidance for further enhancing Jc. 5) We have found that spatial variation in the charge carrier mean free path is responsible for the flux pinning mechanism in the SiCl4 treated MgB2 with large in-field Jc.

Mesoporous metallic rhodium nanoparticles

Mesoporous noble metals are an emerging class of cutting-edge nanostructured catalysts due to their abundant exposed active sites and highly accessible surfaces. Although various noble metal (e.g. Pt, Pd and Au) structures have been synthesized by hard- and soft-templating methods, mesoporous rhodium (Rh) nanoparticles have never been generated via chemical reduction, in part due to the relatively high surface energy of rhodium (Rh) metal. Here we describe a simple, scalable route to generate mesoporous Rh by chemical reduction on polymeric micelle templates [poly(ethylene oxide)-b-poly(methyl methacrylate) (PEO-b-PMMA)]. The mesoporous Rh nanoparticles exhibited a ∼2.6 times enhancement for the electrocatalytic oxidation of methanol compared to commercially available Rh catalyst. Surprisingly, the high surface area mesoporous structure of the Rh catalyst was thermally stable up to 400 °C. The combination of high surface area and thermal stability also enables superior catalytic activity for the remediation of nitric oxide (NO) in lean-burn exhaust containing high concentrations of O2.

First Synthesis of Continuous Mesoporous Copper Films with Uniformly Sized Pores by Electrochemical Soft Templating

Although mesoporous metals have been synthesized by electrochemical methods, the possible compositions have been limited to noble metals (e.g., palladium, platinum, gold) and their alloys. Herein we describe the first fabrication of continuously mesoporous Cu films using polymeric micelles as soft templates to control the growth of Cu under sophisticated electrochemical conditions. Uniformly sized mesopores are evenly distributed over the entire film, and the pore walls are composed of highly crystalized Cu.