Showing papers by "Joselito M. Razal published in 2021"

Superelastic Ti3C2Tx MXene-Based Hybrid Aerogels for Compression-Resilient Devices.

Abstract: Superelastic aerogels with excellent electrical conductivity, reversible compressibility, and high durability hold great potential for varied emerging applications, ranging from wearable electronics to multifunctional scaffolds. In the present work, superelastic MXene/reduced graphene oxide (rGO) aerogels are fabricated by mixing MXene and GO flakes, followed by a multistep reduction of GO, freeze-casting, and finally an annealing process. By optimizing both the composition and reducing conditions, the resultant aerogel shows a reversible compressive strain of 95%, surpassing all current reported values. The conducting MXene/rGO network provides fast electron transfer and stable structural integrity under compression/release cycles. When assembled into compressible supercapacitors, 97.2% of the capacitance was retained after 1000 compression/release cycles. Moreover, the high conductivity and porous structure also enabled the fabrication of a piezoresistive sensor with high sensitivity (0.28 kPa-1), wide detection range (up to 66.98 kPa), and ultralow detection limit (∼60 Pa). It is envisaged that the superelasticity of MXene/rGO aerogels offers a versatile platform for utilizing MXene-based materials in a wide array of applications including wearable electronics, electromagnetic interference shielding, and flexible energy storage devices.

Unipolar stroke, electroosmotic pump carbon nanotube yarn muscles

Abstract: Success in making artificial muscles that are faster and more powerful and that provide larger strokes would expand their applications. Electrochemical carbon nanotube yarn muscles are of special interest because of their relatively high energy conversion efficiencies. However, they are bipolar, meaning that they do not monotonically expand or contract over the available potential range. This limits muscle stroke and work capacity. Here, we describe unipolar stroke carbon nanotube yarn muscles in which muscle stroke changes between extreme potentials are additive and muscle stroke substantially increases with increasing potential scan rate. The normal decrease in stroke with increasing scan rate is overwhelmed by a notable increase in effective ion size. Enhanced muscle strokes, contractile work-per-cycle, contractile power densities, and energy conversion efficiencies are obtained for unipolar muscles.

In situ embedding of cobalt sulfide quantum dots among transition metal layered double hydroxides for high performance all-solid-state asymmetric supercapacitors

Abstract: Layered double hydroxides (LDHs) are widely used as cathode materials for supercapacitors (SCs), thanks to their many advantages. However, the single metal species with limited active sites limit the further improvement of the electrochemical performance of LDH materials. We successfully in situ embedded cobalt sulfide quantum dots (Co9S8-QDs) between the layers of ternary metal LDHs derived from metal–organic-frameworks (MOFs) by selective vulcanization of Co. The prepared Ni3Mn1Co@Co9S8-QDs/NF nanocomposites retain the advantages of LDH materials, such as lower charge transfer resistance. At the same time, the selectively generated ultra-small sized Co9S8-QDs reveal more active sites, which complies with the size minimization strategy, leading to the largely enhanced electrochemical properties. Due to the cooperative effect of LDHs and Co9S8-QDs, the prepared electrode has an excellent capacity (492.1 mA h g−1 at 1 A g−1), remarkable equivalent series resistance (0.499 Ω) and superior capacity retention (90.4% after 10 000 charge–discharge cycles). In addition, the carbon coated Fe2O3 nanoarray is prepared on carbon cloth (CC) as the cathode electrode (Fe2O3@C/CC), and the prepared Ni3Mn1Co@Co9S8-QDs/NF//Fe2O3@C/CC all solid-state asymmetric supercapacitor (ASC) shows an outstanding energy density (71.48 W h kg−1) when the power density is 750 W kg−1 and excellent capacity retention (93.7% after 10 000 charge–discharge cycles). As a result, the construction of composite electrodes with polymetallic LDHs and in situ embedded quantum dots should envision broad prospects.

Development and Applications of MXene-Based Functional Fibers.

Abstract: The increasing interest toward wearable and portable electronic devices calls for multifunctional materials and fibers/yarns capable of seamless integration with everyday textiles. To date, one particular gap inhibiting the development of such devices is the production of robust functional fibers with improved electronic conductivity and electrochemical energy storage capability. Recent efforts have been made to produce functional fibers with 2D carbides known as MXenes to address these demands. Ti3C2Tx MXene, in particular, is known for its metallic conductivity and high volumetric capacitance, and has shown promise for fibers and textile-based devices when used either as an additive, coating or the main fiber component. In this spotlight article, we highlight the recent exciting developments in our diverse efforts to fabricate MXene functionalized fibers, along with a critical evaluation of the challenges in processing, which directly affect macroscale material properties and the performance of the subsequent prototype devices. We also provide our assessment of observed and foreseen challenges of the current manufacturing methods and the opportunities arising from recent advances in the development of MXene fibers and paving future avenues for textile design and practical use in advanced applications.

Interfacial piezoelectric polarization locking in printable Ti3C2Tx MXene-fluoropolymer composites

Abstract: Piezoelectric fluoropolymers convert mechanical energy to electricity and are ideal for sustainably providing power to electronic devices. To convert mechanical energy, a net polarization must be induced in the fluoropolymer, which is currently achieved via an energy-intensive electrical poling process. Eliminating this process will enable the low-energy production of efficient energy harvesters. Here, by combining molecular dynamics simulations, piezoresponse force microscopy, and electrodynamic measurements, we reveal a hitherto unseen polarization locking phenomena of poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) perpendicular to the basal plane of two-dimensional (2D) Ti3C2Tx MXene nanosheets. This polarization locking, driven by strong electrostatic interactions enabled exceptional energy harvesting performance, with a measured piezoelectric charge coefficient, d33, of -52.0 picocoulombs per newton, significantly higher than electrically poled PVDF-TrFE (approximately -38 picocoulombs per newton). This study provides a new fundamental and low-energy input mechanism of poling fluoropolymers, which enables new levels of performance in electromechanical technologies.

Synthesis of petaloid and origami-lantern shaped MnO2/Co2CH@C hierarchical core-shell nanorod arrays for portable asymmetric supercapacitor

Abstract: Freestanding electrodes fabricated with hierarchical core-shell micro-/nano-structured materials synthesized from redox-type metal oxides show enormous potential for portable electronic devices. In this, a novel and facile strategy for the preparation of petaloid and origami-lantern shaped MnO2/Co2CH@C hierarchical porous core-shell nanorod arrays is proposed. The fabricated electrode based on MnO2/Co2CH@C hybrid composite exhibits superior capability of 2022 mF cm−2 under high current density of 5 mA cm−2, which can be explained by the well-oriented petal-like and origami-lantern shaped nanosheets as well as the 3D core-shell porous hierarchical structure. Additionally, a solid-state asymmetric supercapacitor equipment is assembled on basis of the synthesized hierarchical MnO2/Co2CH@C hybrid, exhibiting an energy density of 15 Wh kg−1 at the power density of 255 W kg−1. Notably, the multifunctional instrument can be operated by the assembled device for 8 min, while monitoring time, temperature and air humidity in a portable outdoor environment. Moreover, a blue indicator can also be operated for 9 min long, evidencing their potential commercial applications. Overall, this work demonstrates the promising potential of the synthesized novel origami-lantern shaped and highly oriented hierarchical composites for electrochemical energy storage applications.

A nitrogenous pre-intercalation strategy for the synthesis of nitrogen-doped Ti3C2Tx MXene with enhanced electrochemical capacitance

Abstract: Tremendous efforts have been dedicated towards high-performance energy storage devices though material innovation, nanoscale structural design and hybrid fabrication approaches A crucial technique to tune the properties of nanomaterials, such as MXene, is through introducing defects or heteroatom dopants To improve the level of nitrogen dopant, a two-step pre-intercalation–annealing strategy is developed herein, using ammonium citrate (AC) as an all-in-one intercalant, antioxidant and nitrogen source, followed by annealing in an ammonia atmosphere It is shown that the doping efficiency of nitrogen-doped Ti3C2Tx MXene (N-MXene) increased from 35% to 63%, compared with MXene annealed in ammonia without pre-intercalation This high doping level induces significantly enhanced electrochemical capacitance (475 F g−1 at 5 mV s−1) compared with pristine MXene (321 F g−1), and greatly improved performance at high current density (248 F g−1 at 1 V s−1) Modelling was performed to elucidate the N-doping process of MXene and to understand the mechanism enhancing the electrochemical capacitance, which indicates that the pre-intercalation strategy promotes N-doping as surface functionalization, as well as in the MXene lattice The pre-intercalation strategy demonstrates a new and facile pathway for functionalizing Ti3C2Tx MXene which will facilitate use in applications such as in high performance supercapacitors

Strategies for Integrated Capture and Conversion of CO 2 from Dilute Flue Gases and the Atmosphere

Abstract: Dr. James W. Maina would like to acknowledge Deakin University for his Alfred Deakin Postdoctoral Research Fellowship. Dr. Ludovic F. Dumee acknowledges the Australian Research Council for his Discovery Early Career Research Award (DECRA). Partial financial support from Khalifa University through project RC2-2019-007 is gratefully acknowledged.

Ti3C2Tx MXene: from dispersions to multifunctional architectures for diverse applications

Abstract: The exciting combination of high electrical conductivity, high specific capacitance and colloidal stability of two-dimensional Ti3C2Tx MXene (referred to as MXene) has shown great potential in a wide range of applications including wearable electronics, energy storage, sensors, and electromagnetic interference shielding. To realize its full potential, recent literature has reported a variety of solution-based processing methodologies to develop MXenes into multifunctional architectures, such as fibres, films and aerogels. In response to these recent critical advances, this review provides a comprehensive analysis of the diverse solution-based processing methodologies currently being used for MXene-architecture fabrication. A critical evaluation of the processing challenges directly affecting macroscale material properties and ultimately, the performance of the resulting prototype devices is also provided. Opportunities arising from the observed and foreseen challenges regarding their use are discussed to provide avenues for new designs and realise practical use in high performance applications.

Interfacial Engineering of 3D Hollow Mo-Based Carbide/Nitride Nanostructures.

Abstract: Molybdenum carbide and nitride nanocrystals have been widely recognized as ideal electrocatalyst materials for water splitting. Furthermore, the interfacial engineering strategy can effectively tune their physical and chemical properties to improve performance. Herein, we produced N-doped molybdenum carbide nanosheets on carbonized melamine (N-doped Mo2C@CN) and 3D hollow Mo2C-Mo2N nanostructures (3D H-Mo2C-Mo2N) with tuneable interfacial properties via high-temperature treatment. X-ray photoelectron spectroscopy reveals that Mo2C and Mo2N nanocrystals in 3D hollow nanostructures are chemically bonded with each other and produce stable heterostructures. The 3D H-Mo2C-Mo2N nanostructures demonstrate lower onset potential and overpotential at a current density of 10 mV cm-2 than the N-doped Mo2C@CN nanostructure due to its higher active sites and improved interfacial charge transfer. The current work presents a strategy to tune metal carbide/nitride nanostructures and interfacial properties for the production of high-performance energy materials.

Scalable Fabrication of Ti3C2Tx MXene/RGO/Carbon Hybrid Aerogel for Organics Absorption and Energy Conversion.

Abstract: High aspect ratio two-dimensional Ti3C2Tx MXene flakes with extraordinary mechanical, electrical, and thermal properties are ideal candidates for assembling elastic and conductive aerogels. However, the scalable fabrication of large MXene-based aerogels remains a challenge because the traditional preparation method relies on supercritical drying techniques such as freeze drying, resulting in poor scalability and high cost. Herein, the use of porous melamine foam as a robust template for MXene/reduced graphene oxide aerogel circumvents the volume shrinkage during its natural drying process. Through this approach, we were able to produce large size (up to 600 cm3) MXene-based aerogel with controllable shape. In addition, the aerogels possess an interconnected cellular structure and display resilience up to 70% of compressive strain. Some key features also include high solvent absorption capacity (∼50-90 g g-1), good photothermal conversion ability (an average evaporation rate of 1.48 kg m-2 h-1 for steam generation), and an excellent electrothermal conversion rate (1.8 kg m-2 h-1 at 1 V). More importantly, this passive drying process provides a scalable, convenient, and cost-effective approach to produce high-performance MXene-based aerogels, demonstrating the feasibility of commercial production of MXene-based aerogels toward practical applications.

Light-Controlled Ionic Transport through Molybdenum Disulfide Membranes.

Abstract: In recent years, two-dimensional (2D) nanomaterials have been extensively explored in the field of nanofluidics due to their interconnected and well-controlled nanochannels. In particular, the investigation of 2D nanomaterials using their intrinsic properties for smart nanofluidics is receiving increased interest. Here, we report that MoS2 membranes can be used for light-controlled nanofluidic applications based on their photoelectrical properties. We show that the MoS2 membranes exhibit surface charge-governed ionic transport in NaCl and KCl solution without light illumination, while the ionic conductivity of the MoS2 membranes is up to 2 orders of magnitude higher at low concentration solution than that in bulk solution. We also show that the ionic conductivity of the membranes is enhanced under light illumination at 405 and 635 nm and reversible and stable switching of ionic current upon light illumination is observed. In addition, ionic current through membranes is enhanced by increasing light intensity. Therefore, our findings demonstrate that MoS2 membranes can be a potential platform for light-controlled nanofluidic applications.

Interfacial Piezoelectric Polarization Locking in Printable Ti$_{3}$C$_{2}$T$_{\mathit{x}}$ MXene-Fluoropolymer Composites

Abstract: Piezoelectric fluoropolymers convert mechanical energy to electricity and are ideal for sustainably providing power to electronic devices To convert mechanical energy, a net polarization must be induced in the fluoropolymer, which is currently achieved via an energy intensive electrical poling process Eliminating this process will enable the low-energy production of efficient energy harvesters Here, by combining molecular dynamics simulations, piezoresponse force microscopy, and electrodynamic measurements, we reveal a hitherto unseen polarization locking phenomena of poly(vinylidene fluoride-$\mathit{co}$-trifluoroethylene) (PVDF-TrFE) perpendicular to the basal plane of two-dimensional (2D) Ti$_{3}$C$_{2}$T$_{\mathit{x}}$ MXene nanosheets This polarization locking, driven by strong electrostatic interactions enabled exceptional energy harvesting performance, with a measured piezoelectric charge coefficient, $\mathit{d_{33}}$, of -520 picocoulombs per newton, significantly higher than electrically poled PVDF-TrFE (approximately -38 picocoulombs per newton) This study provides a new fundamental and low energy input mechanism of poling fluoropolymers, which enables new levels of performance in electromechanical technologies

Comparison of silver-plated nylon (Ag/PA66) e-textile and Ag/AgCl electrodes for bioelectrical impedance analysis (BIA).

Abstract: Recently, researchers have adapted Bioelectrical Impedance Analysis (BIA) as a new approach to objectively monitor wounds. They have indicated various BIA parameters associated to specific wound types can be linked to wound healing through trend analysis relative to time. However, these studies are conducted using wet electrodes which have been identified as possessing several shortcomings, such as unstable measurements. Thus, the adaption of e-textile electrodes has become an area of interest in measuring biosignals. E-textile electrodes are known to possess a significantly large polarization impedance (Zp) that potentially influences these biosignal measurements. In this study we aim to identify the suitability of e-textile electrodes to monitor wounds using BIA methodologies. By adapting suggested methodologies conducted in-vivo from previous studies, we used an ex-vivo model to observe the behaviour of e-textile electrodes relative to time. This was compared to common clinical wet electrodes, specifically Ag/AgCl. The objective of this study was to identify the BIA parameters that can be used to monitor wounds with e-textile electrodes. By analysing the BIA parameters relative to time, we observed the influence ofZpon these parameters.