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| 3. |
- Shokeir, Mohamed, et al.
(författare)
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Influence of Graphene, SiCnp, and G/SiCnp Hybrid Fillers on the Strengthening Mechanisms of Al-Matrix
- 2020
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Ingår i: Metallurgical and Materials Transactions. A. - : SPRINGER. - 1073-5623 .- 1543-1940. ; 51:6, s. 3280-3298
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Tidskriftsartikel (refereegranskat)abstract
- AA2124 reinforced with graphene (G), silicon carbide nanoparticles (SiCnp), and graphene-coated SiCnp (GCSiC(np)) were fabricated and characterized. GCSiC(np) reinforcement was fabricated by ball milling, followed by mixing and milling the reinforcements with AA2124 powders. Consolidation was achieved by cold compaction and hot extrusion (HE). The powders morphology and structural evolution were characterized with XRD and SEM. Microhardness and tensile properties were also characterized. Increasing the fillers content beyond 5 wt pct deteriorated the composites mechanical properties due to the agglomeration of the fillers. Adding 5 wt pct GCSiC(np) increased the hardness, specific strength, and modulus of the composite and decreased ductility. Furthermore, 5 wt pct SiCnp induced severe lattice strain by intra-granular dispersion strengthening. The GCSiC(np) filler strengthened the Al-matrix via the strong interfacial bonding of the intercalated inter-granular lamination of the hybrid particles within the Al-matrix and the intra-granular dispersion strengthening associated with the individual SiCnp. Adding 5 wt pct G lowered the HE composites density and hardness significantly, while the sliding of G-intercalated layers coating the Al-grains facilitated plastic flow along the extrusion direction and enhanced the strength and ductility of the composite compared to that containing 5 wt pct GCSiC(np).
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| 4. |
- Ahmed, Bilal, et al.
(författare)
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Electrochemical activation of commercial graphite sheets for supercapacitive applications
- 2022
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Ingår i: Electrochimica Acta. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0013-4686 .- 1873-3859. ; 431
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Tidskriftsartikel (refereegranskat)abstract
- Carbon-based substrates are widely used as current collectors for high-performance energy storage materials in supercapacitors. However, these substrates exhibit negligible charge storage due to inferior electrochemical activity and small surface area. Herein, electrochemical activation is utilized to enhance the electrochemical activity of - inherently inactive - commercial graphite sheets for supercapacitive applications. The results reveal that the electrochemically activated graphite sheets render a 30-fold increase in areal capacitance, i.e., from 22 to 447 mF cm(-2), which can be ascribed to the activation of graphite oxide functional groups on the surface. Also, the influence of electrochemical activation time on electrochemical performance is explored in detail, followed by the fabrication and characterization of symmetric supercapacitors based on the optimum process parameters in single-cell and tandem configurations, demonstrating the potential of electrochemically activated graphite sheets in practical applications.
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| 5. |
- Ahmed, Bilal, et al.
(författare)
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i-MXenes for Energy Storage and Catalysis
- 2020
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Ingår i: Advanced Functional Materials. - : WILEY-V C H VERLAG GMBH. - 1616-301X .- 1616-3028. ; 30:47
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Tidskriftsartikel (refereegranskat)abstract
- In 2017, a new family of in-plane, chemically-ordered quaternary MAX phases, coined i-MAX, has been reported since 2017. The first i-MAX phase, (Mo2/3Sc1/3)(2)AlC, garnered significant research attention due to the presence of chemically ordered Sc within the Mo-dominated M layer, and the facilitated removal of both Al and Sc upon etching, resulting in 2D i-MXene, Mo1.33C, with ordered divacancies. The i-MXene renders an exceptionally low resistivity of 33.2 mu omega m(-1) and a high volumetric capacitance of approximate to 1150 F cm(-3). This discovery has been followed by the synthesis of, to date, 32 i-MAX phases and 5 i-MXenes, where the latter have shown potential for applications including, but not limited to, energy storage and catalysis. Herein, fundamental investigations of i-MAX phases and i-MXenes, along with their applicability in supercapacitive and catalytic applications, are reviewed. Moreover, recent results on ion intercalation and post-etching treatment of Mo1.33C are presented. The charge storage performance can also be tuned by forming MXene hydrogel and through inert atmosphere annealing, where the latter renders a superior volumetric capacitance of approximate to 1635 F cm(-3). This report demonstrates the potential of the i-MXene family for catalytic and energy storage applications, and highlights novel research directions for further development and successful employment in practical applications.
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| 6. |
- Ahmed, Heba, et al.
(författare)
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Recovery of oxidized two-dimensional MXenes through high frequency nanoscale electromechanical vibration
- 2023
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Ingår i: Nature Communications. - : NATURE PORTFOLIO. - 2041-1723. ; 14:1
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Tidskriftsartikel (refereegranskat)abstract
- MXenes hold immense potential given their superior electrical properties. The practical adoption of these promising materials is, however, severely constrained by their oxidative susceptibility, leading to significant performance deterioration and lifespan limitations. Attempts to preserve MXenes have been limited, and it has not been possible thus far to reverse the materials performance. In this work, we show that subjecting oxidized micron or nanometer thickness dry MXene films-even those constructed from nanometer-order solution-dispersed oxidized flakes-to just one minute of 10 MHz nanoscale electromechanical vibration leads to considerable removal of its surface oxide layer, whilst preserving its structure and characteristics. Importantly, electrochemical performance is recovered close to that of their original state: the pseudocapacitance, which decreased by almost 50% due to its oxidation, reverses to approximately 98% of its original value, with good capacitance retention ( approximate to 93%) following 10,000 charge-discharge cycles at 10 A g(-1). These promising results allude to the exciting possibility for rejuvenating the material for reuse, therefore offering a more economical and sustainable route that improves its potential for practical translation. Despite their vast potential, the practical deployment of MXenes has been hampered by their tendency to be oxidized. Here, the authors show that simply vibrating MXene films in just a minute can remove the oxide layer formed and restore their electrochemical performance close to its original state.
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| 7. |
- Ahmed, Heba, et al.
(författare)
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Ultrafast assembly of swordlike Cu-3(1,3,5-benzenetricarboxylate)(n) metal-organic framework crystals with exposed active metal sites
- 2020
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Ingår i: Nanoscale Horizons. - : ROYAL SOC CHEMISTRY. - 2055-6764 .- 2055-6756. ; 5:7, s. 1050-1057
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Tidskriftsartikel (refereegranskat)abstract
- Owing to their large surface area and high uptake capacity, metal-organic frameworks (MOFs) have attracted considerable attention as potential materials for gas storage, energy conversion, and electrocatalysis. Various strategies have recently been proposed to manipulate the MOF surface chemistry to facilitate exposure of the embedded metal centers at the crystal surface to allow more effective binding of target molecules to these active sites. Nevertheless, such strategies remain complex, often requiring strict control over the synthesis conditions to avoid blocking pore access, reduction in crystal quality, or even collapse of the entire crystal structure. In this work, we exploit the hydrodynamics and capillary resonance associated with acoustically-driven dynamically spreading and nebulizing thin films as a new method for ultrafast synthesis of swordlike Cu-3(1,3,5-benzenetricarboxylate)(n) (Cu-BTC) MOFs with unique monoclinic crystal structures (P2(1)/n) distinct to that obtained via conventional bulk solvothermal synthesis, with swordlike morphologies whose lengths far exceed their thicknesses. Through pulse modulation and taking advantage of the rapid solvent evaporation associated with the high nebulisation rates, we are also able to control the thicknesses of these large aspect ratio (width and length with respect to the thickness) crystals by arresting their vertical growth, which, in turn, allows exposure of the metal active sites at the crystal surface. An upshot of such active site exposure on the crystal surface is the concomitant enhancement in the conductivity of the MOF, evident from the improvement in its current density by two orders of magnitude.
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| 8. |
- Alijani, Hossein, et al.
(författare)
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Acoustomicrofluidic Synthesis of Pristine Ultrathin Ti3C2Tz MXene Nanosheets and Quantum Dots
- 2021
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Ingår i: ACS Nano. - : AMER CHEMICAL SOC. - 1936-0851 .- 1936-086X. ; 15:7, s. 12099-12108
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Tidskriftsartikel (refereegranskat)abstract
- The conversion of layered transition metal carbides and/or nitrides (MXenes) into zero-dimensional structures with thicknesses and lateral dimensions of a few nanometers allows these recently discovered materials with exceptional electronic properties to exploit the additional benefits of quantum confinement, edge effects, and large surface area. Conventional methods for the conversion of MXene nanosheets and quantum dots, however, involve extreme conditions such as high temperatures and/or harsh chemicals that, among other disadvantages, lead to significant degradation of the material as a consequence of their oxidation. Herein, we show that the large surface acceleration.on the order of 10 million gs.produced by high-frequency (10 MHz) nanometer-order electromechanical vibrations on a chipscale piezoelectric substrate is capable of efficiently nebulizing, and consequently dimensionally reducing, a suspension of multilayer Ti3C2Tz (MXene) into predominantly monolayer nanosheets and quantum dots while, importantly, preserving the material from any appreciable oxidation. As an example application, we show that the high-purity MXene quantum dots produced using this room-temperature chemical-free synthesis method exhibit superior performance as electrode materials for electrochemical sensing of hydrogen peroxide compared to the highly oxidized samples obtained through conventional hydrothermal synthesis. The ability to detect concentrations as low as 5 nM is a 10-fold improvement to the best reported performance of Ti3C2Tz MXene electrochemical sensors to date.
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| 9. |
- El Ghazaly, Ahmed
(författare)
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Acoustic Platform for MXene Synthesis and Electrochemical Behaviour of i-MXenes in Aqueous Electrolytes
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Climate Change is believed to be the greatest global challenge and on its forefront is the topic of energy. While being of extreme importance, debates over energy have become a normality. The related field of material synthesis for energy storage applications has also been growing, as well as the demand for industrial electrification from renewable sources of energy. Water-based supercapacitors are a type of energy storage devices that can deliver high power densities while maintaining long term cyclability in an environmen-tally friendly media. However, their challenges include maintaining high per-formance in term of energy density, safety, and low cost of electrode manu-facturing. MXene is family of two-dimensional transition metal carbides/nitrides that are terminated with H, OH and F groups. The material demonstrates superior physical and chemical properties related to energy applications in compari-son to its 3D parent material, the MAX phase. Since its discovery in 2011, MXene, such as Ti3C2Tz, has been widely investigated in the field of energy storage due to its high conductivity (20,000 S.cm-1) and a volumetric capac-itance that can reach 900 Fcm-3. However, reported synthesis processes for MXene are fraught with hazardous procedures that are time consuming. The first section of this thesis presents a new innovative method for Ti3C2Tz MXene synthesis, in which MXene was synthesized in a few milliseconds with the assistance of 30 MHz frequency surface acoustic waves (SAW) and 0.05M of LiF. The aluminium element in the Ti3AlC2 MAX phase was etched by so called “localized HF”, and the powder was converted to 2D Ti3C2Tz. This method showed resulting MXene comparable to that of previ-ously reported synthesis techniques, as demonstrated by the material’s elec-trochemical performance. The second section of the thesis focuses on investigating the electrochemical performance of a comparatively new family of MXene, coined i-MXene, in aqueous electrolyte. i-MXene, reported in 2017, has the chemical formula Mo1.33CTz and is a product of chemical etching of the in-plane chemically ordered (Mo2/3Sc1/3)2AlC i-MAX phase. The Mo1.33CTz was studied in a sul-phuric acid electrolyte. This electrolyte sets a limit for the electrode potential window and capacitance, and therefore, post-synthesis treatment protocols was used to enhance the electrochemical performance. The Mo1.33CTz recorded a volumetric capacitance of 1050 Fcm-3 and1600 Fcm-3 for hydrogel treatment and heat-treated electrodes, respectively. Moreover, mixing Mo1.33CTz with MoS2 and graphene improved both the specific capacitance and the electrode stability even further. The electrochemical properties of Mo1.33CTz were thereafter explored in dif-ferent sulfate-based aqueous electrolytes with univalent (Li+, Na+, and K+) and divalent (Mg2+ Mn2+ or Zn2+) cations. Mo1.33CTz exhibited a wider po-tential window without degradation, expanding the previously reported limit in sulphuric acid for both symmetric and asymmetric devices. Lithium chlo-ride gave the best results, being an electrolyte based on a natural salt that has high solubility at room temperature. It presented a large potential window, -1.2 to +0.3V (vs. Ag/AgCl), and a volumetric capacitance of ~800 Fcm−3 at a scan rate of 2 mVs−1. In addition, the performance of a Mo1.33CTz //MnxOn asymmetric device was tested in 5M LiCl electrolyte. The results showed a potential window of 2 V, a volumetric energy density of 58 mWhcm-3, and a 100% columbic efficiency after 10,000 charge/discharge cycles. A cyclic sta-bility is crucial for practical applications, and altogether, the promising re-sults motivate further exploration of i-MXenes for energy storage and be-yond.
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| 10. |
- El Ghazaly, Ahmed, et al.
(författare)
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Enhanced supercapacitive performance of Mo1.33C MXene based asymmetric supercapacitors in lithium chloride electrolyte
- 2021
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Ingår i: Energy Storage Materials. - : Elsevier. - 2405-8289 .- 2405-8297. ; 41, s. 203-208
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Tidskriftsartikel (refereegranskat)abstract
- Two-dimensional (2D) Mo1.33C MXene renders great potential for energy storage applications and is mainly studied in the sulfuric acid (H2SO4) electrolyte. However, H2SO4 limits the electrode potential to 0.9 V for symmetric devices and 1.3 V for asymmetric devices. Herein, we explore the electrochemical behavior of Mo1.33C MXene in LiCl electrolyte. In comparison to H2SO4, LiCl electrolyte is a neutral salt with high solubility at room temperature and low hazardousness. The analysis shows a volumetric capacitance of 815 Fcm(-3) at a scan rate of 2 mVs(-1) with a large operating potential window of -1.2 to +0.3V (vs. Ag/AgCl). This is further exploited to construct MXene-based asymmetric supercapacitors Mo1.33C//MnxOn, and the electrochemical performance is evaluated in 5M LiCl electrolyte. Owing to the wide voltage widow of the Mo1.33C//MnxOn devices (2V) and high packing density of the electrodes, we have achieved a volumetric energy density of 58 mWh/cm(3), a maximum power density of 31 Wcm(-3) and retained 92% of the initial capacitance after 10,000 charge/discharge cycles at 10 A g(-1). One of the main value propositions of this work, aside from the high energy density, is the outstanding columbic efficiency (100%), which ensures excellent cyclic stability and is highly desirable for practical applications.
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