Valeria Nicolosi - Academia.edu (original) (raw)

Papers by Valeria Nicolosi

Journal of materials chemistry. A, Materials for energy and sustainability, 2019

MXenes are emerging as a very promising electrode material of highperformance micro-supercapacito... more MXenes are emerging as a very promising electrode material of highperformance micro-supercapacitors (MSCs) for microscale electronics. However, MXene based MSCs (M-MSCs) reported so far exhibit low areal (#10 mW h cm 2) and volumetric (#20 mW h cm 3) energy densities due to their narrow working voltage in aqueous systems (0.6-1.0 V). Herein, we report for the first time the construction of high-voltage and high-energy flexible ionogel-based M-MSCs with interdigital microelectrodes of ionic liquid preintercalated MXene films. Benefitting from the pre-intercalation of ionic liquid, the as-fabricated M-MSCs, working at 3 V in 1-ethyl-3methylimidazolium tetrafluoroborate (EMIMBF4), exhibited high areal and volumetric energy densities of 13.9 mW h cm 2 and 43.7 mW h cm 3 , respectively, both of which are among the highest values for the reported M-MSCs. Moreover, all-solid-state M-MSCs using ionogel electrolytes displayed exceptional flexibility without capacitance loss under various deformation conditions and seamless integration free of metal-based interconnections for boosting voltage output. Therefore, such high-energy M-MSCs hold great potential for direct integration of flexible and miniature electronics.

Nature Communications

2D material hydrogels have recently sparked tremendous interest owing to their potential in diver... more 2D material hydrogels have recently sparked tremendous interest owing to their potential in diverse applications. However, research on the emerging 2D MXene hydrogels is still in its infancy. Herein, we show a universal 4D printing technology for manufacturing MXene hydrogels with customizable geometries, which suits a family of MXenes such as Nb2CTx, Ti3C2Tx, and Mo2Ti2C3Tx. The obtained MXene hydrogels offer 3D porous architectures, large specific surface areas, high electrical conductivities, and satisfying mechanical properties. Consequently, ultrahigh capacitance (3.32 F cm−2 (10 mV s−1) and 233 F g−1 (10 V s−1)) and mass loading/thickness-independent rate capabilities are achieved. The further 4D-printed Ti3C2Tx hydrogel micro-supercapacitors showcase great low-temperature tolerance (down to –20 °C) and deliver high energy and power densities up to 93 μWh cm−2 and 7 mW cm−2, respectively, surpassing most state-of-the-art devices. This work brings new insights into MXene hydrog...

Potassium ion hybrid capacitors (KICs) have drawn tremendous attention for large-scale energy sto... more Potassium ion hybrid capacitors (KICs) have drawn tremendous attention for large-scale energy storage applications because of their high energy and power densities and the abundance of potassium sources. However, achieving KICs with high capacity and long lifespan remains challenging because the large size of potassium ions causes sluggish kinetics and fast structural pulverization of electrodes. Here, we report a composite anode of VO 2 −V 2 O 5 nanoheterostructures captured by a 3D N-doped carbon network (VO 2 −V 2 O 5 /NC) that exhibits a reversible capacity of 252 mAh g −1 at 1 A g −1 over 1600 cycles and a rate performance with 108 mAh g −1 at 10 A g −1. Quantitative kinetics analyses demonstrate that such great rate capability and cyclability are enabled by the capacitivedominated potassium storage mechanism in the interfacial engineered VO 2 −V 2 O 5 nanoheterostructures. The further fabricated full KIC cell consisting of a VO 2 −V 2 O 5 /NC anode and an active carbon cathode delivers a high operating voltage window of 4.0 V and energy and power densities up to 154 Wh kg −1 and 10 000 W kg −1 , respectively, surpassing most state-ofthe-art KICs.

At present, the world is at the peak of production of traditional fossil fuels. Much of the resou... more At present, the world is at the peak of production of traditional fossil fuels. Much of the resources that humanity has been consuming (oil, coal and natural gas) are coming to an end. The human being faces a future that must necessarily go through a paradigm shift, which includes a progressive movement towards increasingly less polluting and energetically viable resources. In this sense, nanotechnology has a transcendental role in this change. For decades, new materials capable of being used in energy processes have been synthesized that undoubtedly will be the cornerstone of the future development of the planet. In this review, we report on the current progress in the synthesis and use of one-dimensional (1D) nanostructured materials (specifically nanowires, nanofibers, nanotubes and nanorods), with compositions based on oxides, nitrides, or metals, for applications related to energy. Due to its extraordinary surface-volume relationship, tunable thermal and transport properties, a...

npj 2D Materials and Applications, 2021

Batteries are the most abundant form of electrochemical energy storage. Lithium and sodium ion ba... more Batteries are the most abundant form of electrochemical energy storage. Lithium and sodium ion batteries account for a significant portion of the battery market, but high-performance electrochemically active materials still need to be discovered and optimized for these technologies. Recently, tin(II) oxide (SnO) has emerged as a highly promising battery electrode. In this work, we present a facile synthesis method to produce SnO microparticles whose size and shape can be tailored by changing the solvent nature. We study the complex relationship between wet-chemistry synthesis conditions and resulting layered nanoparticle morphology. Furthermore, high-level electronic structure theory, including dispersion corrections to account for van der Waals forces, is employed to enhance our understanding of the underlying chemical mechanisms. The electronic vacuum alignment and surface energies are determined, allowing the prediction of the thermodynamically favoured crystal shape (Wulff const...

ACS Nano, 2021

The fast development of terahertz technologies demands high-performance electromagnetic interfere... more The fast development of terahertz technologies demands high-performance electromagnetic interference (EMI) shielding materials to create safe electromagnetic environments. Despite tremendous breakthroughs in achieving superb shielding efficiency (SE), conventional shielding materials have high reflectivity and cannot be re-edited or recycled once formed, resulting in detrimental secondary electromagnetic pollution and poor adaptability. Herein, a hydrogel-type shielding material incorporating MXene and poly(acrylic acid) is fabricated through a biomineralization-inspired assembly route. The composite hydrogel exhibits excellent stretchability and recyclability, favorable shape adaptability and adhesiveness, and fast self-healing capability, demonstrating great application flexibility and reliability. More interestingly, the shielding performance of the hydrogel shows absorption-dominated feature due to the combination of the porous structure, moderate conductivity, and internal water-rich environment. High EMI SE of 45.3 dB and broad effective absorption bandwidth (0.2−2.0 THz) with excellent refection loss of 23.2 dB can be simultaneously achieved in an extremely thin hydrogel (0.13 mm). Furthermore, such hydrogel demonstrates sensitive deformation responses and can be used as an on-skin sensor. This work provides not only an alternative strategy for designing next-generation EMI shielding material but also a highly efficient and convenient method for fabricating MXene composite on macroscopic scales.

Advanced Energy Materials, 2020

Increasing the energy density of lithium‐ion batteries requires the discovery of new electrode ma... more Increasing the energy density of lithium‐ion batteries requires the discovery of new electrode materials capable of achieving very high areal capacity. Here, liquid phase exfoliation is used to produce nanosheets of SnP3, a 2D material with extremely high theoretical capacity of 1670 mAh g−1. These nanosheets can be fabricated into solution‐processed thin films for use as lithium storing anodes. To maximize their performance, carbon nanotubes are incorporated into the electrodes to simultaneously enhance conductivity and toughness. As a result, electrodes of thickness >300 µm can be produced, which display active‐mass‐normalized capacities (≈1657 mAh g−1Active) very close to the theoretical value. These materials show maximum specific (≈1250 mAh g−1Electrode) and areal (>20 mAh cm−2) capacities, which are at the state‐of‐the‐art for 2D‐based electrodes, coupled with good rate performance and stability. In combination with commercial cathode materials, full‐cells are fabricated...

Advanced Optical Materials, 2020

Two‐photon absorption (2PA) is a nonlinear optical (NLO) effect that typically occurs in a conven... more Two‐photon absorption (2PA) is a nonlinear optical (NLO) effect that typically occurs in a conventional semiconductor whose bandgap is larger than the energy of one excited photon but smaller than the energy of two photons. In this work, the experimental observation of strong 2PA in gapless MXene monolayers is reported. This phenomenon is verified by a nonlinear transmission method and ultrafast dynamic studies based on a wavelength‐degenerate, non‐collinear pump‐probe technique. The unconventional 2PA is attributed to the structures of the MXene energy bands near the Fermi level, which favors two‐photon transitions and suppresses one‐photon transitions due to parallel band absorption effects. These results, as well as the measured NLO parameters including the 2PA coefficient, absorption cross‐section, excited carrier lifetimes, and third‐order NLO susceptibility, provide a systematic understanding of the unusual NLO effect in MXenes and may be applied in advanced photonic and optoe...

Materials Today, 2019

The consumer demand for flexible wearables has increased rapidly with the advent of recent commer... more The consumer demand for flexible wearables has increased rapidly with the advent of recent commercial health monitoring systems. The progress in wearable electronics for monitoring physiological parameters in the healthcare industry is rapid and its adaptation is having a positive impact on society. Physiological parameters are important health indicators and their monitoring could effectively enable early detection of disease. This would also help reduce the number of more severe health problems, in disease prevention and lower the overall public sector health cost. Clinical devices for measurement of these parameters are also traditionally non-wearable. Therefore, companies and researchers are focused on the development of new materials and related manufacturing methods which will enable specific wearable health sensors with a high degree of robustness, repeatability and accuracy. On the development of printed physiological signal monitoring devices, much progress has been achieved in recent years. Eventhough several reviews have been presented on flexible and wearable electronics, a detailed summary of the recent progresses on the specific class of printed physiological signal monitoring sensing devices has not been reported. In this review, recent progress and challenges on the functional inks and substrate materials for mass scale production and customization of printed flexible and wearable physiological signal monitoring sensor devices are summarized.

Scientific Reports, 2019

Considerable attention has been drawn to the lead halide perovskites (LHPs) because of their outs... more Considerable attention has been drawn to the lead halide perovskites (LHPs) because of their outstanding optoelectronic characteristics. LHP nanosheets (NSs) grown from single crystalline lead halide possess advantages in device applications as they provide the possibility for control over morphology, composition, and crystallinity. Here, free-standing lead bromide (PbBr2) single-crystalline NSs with sizes up to one centimeter are synthesized from solution. These NSs can be converted to LHP while maintaining the NS morphology. We demonstrate that these perovskite NSs can be processed directly for fabrication of photodetector and laser arrays on a large scale. This strategy will allow high-yield synthesis of large-size perovskite NSs for functional devices in an integrated photonics platform.

Applied Physics Letters, 2017

Tailoring the electrical properties of transition metal dichalcogenides by doping is one of the b... more Tailoring the electrical properties of transition metal dichalcogenides by doping is one of the biggest challenges for the application of 2D materials in future electronic devices. Here, we report on a straightforward approach to the n-type doping of molybdenum disulfide (MoS2) films with rhenium (Re). High-Resolution Scanning Transmission Electron Microscopy and Energy-Dispersive X-ray spectroscopy are used to identify Re in interstitial and lattice sites of the MoS2 structure. Hall-effect measurements confirm the electron donating influence of Re in MoS2, while the nominally undoped films exhibit a net p-type doping. Density functional theory (DFT) modelling indicates that Re on Mo sites is the origin of the n-type doping, whereas S-vacancies have a p-type nature, providing an explanation for the p-type behaviour of nominally undoped MoS2 films.

Nature Communications, 2019

One weakness of batteries is the rapid falloff in charge-storage capacity with increasing charge/... more One weakness of batteries is the rapid falloff in charge-storage capacity with increasing charge/discharge rate. Rate performance is related to the timescales associated with charge/ionic motion in both electrode and electrolyte. However, no general fittable model exists to link capacity-rate data to electrode/electrolyte properties. Here we demonstrate an equation which can fit capacity versus rate data, outputting three parameters which fully describe rate performance. Most important is the characteristic time associated with charge/discharge which can be linked by a second equation to physical electrode/electrolyte parameters via various rate-limiting processes. We fit these equations to ~200 data sets, deriving parameters such as diffusion coefficients or electrolyte conductivities. It is possible to show which rate-limiting processes are dominant in a given situation, facilitating rational design and cell optimisation. In addition, this model predicts the upper speed limit for ...

Nature Communications, 2019

Direct printing of functional inks is critical for applications in diverse areas including electr... more Direct printing of functional inks is critical for applications in diverse areas including electrochemical energy storage, smart electronics and healthcare. However, the available printable ink formulations are far from ideal. Either surfactants/additives are typically involved or the ink concentration is low, which add complexity to the manufacturing and compromises the printing resolution. Here, we demonstrate two types of two-dimensional titanium carbide (Ti3C2Tx) MXene inks, aqueous and organic in the absence of any additive or binary-solvent systems, for extrusion printing and inkjet printing, respectively. We show examples of all-MXene-printed structures, such as micro-supercapacitors, conductive tracks and ohmic resistors on untreated plastic and paper substrates, with high printing resolution and spatial uniformity. The volumetric capacitance and energy density of the all-MXene-printed micro-supercapacitors are orders of magnitude greater than existing inkjet/extrusion-print...

Journal of Materials Chemistry A, 2019

Ionogel-based flexible micro-supercapacitors are constructed based on interdigital microelectrode... more Ionogel-based flexible micro-supercapacitors are constructed based on interdigital microelectrodes of ionic liquid pre-intercalated MXene compact films.

ACS Applied Nano Materials, 2018

Carbon nanofoam (CNF) is a low-density, high-surface-area material formed by aggregation of amorp... more Carbon nanofoam (CNF) is a low-density, high-surface-area material formed by aggregation of amorphous carbon nanoparticles into porous nanostructures. We report the use of a pulsed infrared laser to prepare CNF from a graphene oxide (GO) target material. Electron microscopy shows that the films consist of dendritic strings which form web-like three-dimensional structures. The conductivity of these structures can be modified by using the CNF as a nanostructured scaffold for gold nanoparticles deposited by sputter coating, controllably increasing the conductivity by up to four orders of magnitude. The ability to measure the conductivity of the porous structures allows electrochemical measurements in the environment. Upon decreasing humidity, the pristine CNF exhibits an increase in resistance with a quick response and recovery time. By contrast, the goldsputtered CNF showed a decrease in resistance, indicating modification of the doping mechanism due to water adsorption. The sensitivity to humidity is eliminated at the percolation threshold of the metal on the CNF.

Advanced science (Weinheim, Baden-Wurttemberg, Germany), 2018

Sulfur (S) is an attractive cathode material with advantages including high theoretical capacity ... more Sulfur (S) is an attractive cathode material with advantages including high theoretical capacity and low cost. However, issues such as the lithium polysulfide shuttle effect and its insulating properties greatly limit the future applications of lithium-sulfur (Li-S) batteries. Here, a viscous aqueous ink with nanoscale S uniformly decorated on the polar, metallically conductive titanium carbide MXene nanosheets (S@TiCT ) is reported to address these issues. Importantly, it is observed that the conductive TiCT mediator efficiently chemisorbs the soluble polysulfides and converts them into thiosulfate/sulfate. The in situ formed sulfate complex layer acts as a thick protective barrier, which significantly retards the shuttling of polysulfides upon cycling and improves the sulfur utilization. Consequently, the binder-free, robust, highly electrically conductive composite film exhibits outstanding electrochemical performance, including high capacities (1244-1350 mAh g), excellent rate h...

Scientific reports, Jan 8, 2018

This paper describes the wet-chemistry synthesis of highly crystalline hexagonal flakes of Ni-Fe ... more This paper describes the wet-chemistry synthesis of highly crystalline hexagonal flakes of Ni-Fe layered double hydroxide (LDH) produced at temperature as low as 100 °C. The flakes with diameter in the range of 0.5-1.5 μm and the thickness between 15 and 20 nm were obtained by homogeneous precipitation method with the use of triethanolamine (TEA) and urea. By analyzing the intermediate products, it is suggested that, differently from previous reports, a thermodynamically metastable iron oxyhydroxide and Ni-TEA complex are firstly formed at room temperature. Subsequently, when the mixture is heated to 100 °C and the pH increases due to the thermal decomposition of urea, Ni and Fe are slowly released and then recombine, thus leading to formation of pure, highly-crystalline Ni-Fe LDH flakes. This material showed promising results as an electrocatalyst in oxygen evolution reaction (OER) providing an overpotential value of 0.36 V.

npj 2D Materials and Applications, 2017

Titanium (IV) sulphide (TiS2) is a layered transition metal dichalcogenide, which we exfoliate us... more Titanium (IV) sulphide (TiS2) is a layered transition metal dichalcogenide, which we exfoliate using liquid phase exfoliation. TiS2 is a candidate for being part of a range of future technologies. These applications are varied, and include supercapacitor and battery energy storage devices, catalytic substrates and the splitting of water. The driving force behind our interest was as a material for energy storage devices. Here we investigate a potential failure mechanism for such devices, namely oxidation and subsequent loss of sulphur. This degradation is important to understand, since these applications are highly property-dependent, and changes to the chemistry will result in changes in desired properties. Two approaches to study oxidisation were taken: ex situ oxidation by water and oxygen at room temperature and in situ oxidation by a 5% O2/Ar gas at elevated temperatures. Both sources of oxygen resulted in oxidation of the starting TiS2 flakes, with differing morphologies. Water...

Microscopy and Microanalysis, 2015

Journal of materials chemistry. A, Materials for energy and sustainability, 2019

MXenes are emerging as a very promising electrode material of highperformance micro-supercapacito... more MXenes are emerging as a very promising electrode material of highperformance micro-supercapacitors (MSCs) for microscale electronics. However, MXene based MSCs (M-MSCs) reported so far exhibit low areal (#10 mW h cm 2) and volumetric (#20 mW h cm 3) energy densities due to their narrow working voltage in aqueous systems (0.6-1.0 V). Herein, we report for the first time the construction of high-voltage and high-energy flexible ionogel-based M-MSCs with interdigital microelectrodes of ionic liquid preintercalated MXene films. Benefitting from the pre-intercalation of ionic liquid, the as-fabricated M-MSCs, working at 3 V in 1-ethyl-3methylimidazolium tetrafluoroborate (EMIMBF4), exhibited high areal and volumetric energy densities of 13.9 mW h cm 2 and 43.7 mW h cm 3 , respectively, both of which are among the highest values for the reported M-MSCs. Moreover, all-solid-state M-MSCs using ionogel electrolytes displayed exceptional flexibility without capacitance loss under various deformation conditions and seamless integration free of metal-based interconnections for boosting voltage output. Therefore, such high-energy M-MSCs hold great potential for direct integration of flexible and miniature electronics.

Nature Communications

2D material hydrogels have recently sparked tremendous interest owing to their potential in diver... more 2D material hydrogels have recently sparked tremendous interest owing to their potential in diverse applications. However, research on the emerging 2D MXene hydrogels is still in its infancy. Herein, we show a universal 4D printing technology for manufacturing MXene hydrogels with customizable geometries, which suits a family of MXenes such as Nb2CTx, Ti3C2Tx, and Mo2Ti2C3Tx. The obtained MXene hydrogels offer 3D porous architectures, large specific surface areas, high electrical conductivities, and satisfying mechanical properties. Consequently, ultrahigh capacitance (3.32 F cm−2 (10 mV s−1) and 233 F g−1 (10 V s−1)) and mass loading/thickness-independent rate capabilities are achieved. The further 4D-printed Ti3C2Tx hydrogel micro-supercapacitors showcase great low-temperature tolerance (down to –20 °C) and deliver high energy and power densities up to 93 μWh cm−2 and 7 mW cm−2, respectively, surpassing most state-of-the-art devices. This work brings new insights into MXene hydrog...

Potassium ion hybrid capacitors (KICs) have drawn tremendous attention for large-scale energy sto... more Potassium ion hybrid capacitors (KICs) have drawn tremendous attention for large-scale energy storage applications because of their high energy and power densities and the abundance of potassium sources. However, achieving KICs with high capacity and long lifespan remains challenging because the large size of potassium ions causes sluggish kinetics and fast structural pulverization of electrodes. Here, we report a composite anode of VO 2 −V 2 O 5 nanoheterostructures captured by a 3D N-doped carbon network (VO 2 −V 2 O 5 /NC) that exhibits a reversible capacity of 252 mAh g −1 at 1 A g −1 over 1600 cycles and a rate performance with 108 mAh g −1 at 10 A g −1. Quantitative kinetics analyses demonstrate that such great rate capability and cyclability are enabled by the capacitivedominated potassium storage mechanism in the interfacial engineered VO 2 −V 2 O 5 nanoheterostructures. The further fabricated full KIC cell consisting of a VO 2 −V 2 O 5 /NC anode and an active carbon cathode delivers a high operating voltage window of 4.0 V and energy and power densities up to 154 Wh kg −1 and 10 000 W kg −1 , respectively, surpassing most state-ofthe-art KICs.

At present, the world is at the peak of production of traditional fossil fuels. Much of the resou... more At present, the world is at the peak of production of traditional fossil fuels. Much of the resources that humanity has been consuming (oil, coal and natural gas) are coming to an end. The human being faces a future that must necessarily go through a paradigm shift, which includes a progressive movement towards increasingly less polluting and energetically viable resources. In this sense, nanotechnology has a transcendental role in this change. For decades, new materials capable of being used in energy processes have been synthesized that undoubtedly will be the cornerstone of the future development of the planet. In this review, we report on the current progress in the synthesis and use of one-dimensional (1D) nanostructured materials (specifically nanowires, nanofibers, nanotubes and nanorods), with compositions based on oxides, nitrides, or metals, for applications related to energy. Due to its extraordinary surface-volume relationship, tunable thermal and transport properties, a...

npj 2D Materials and Applications, 2021

Batteries are the most abundant form of electrochemical energy storage. Lithium and sodium ion ba... more Batteries are the most abundant form of electrochemical energy storage. Lithium and sodium ion batteries account for a significant portion of the battery market, but high-performance electrochemically active materials still need to be discovered and optimized for these technologies. Recently, tin(II) oxide (SnO) has emerged as a highly promising battery electrode. In this work, we present a facile synthesis method to produce SnO microparticles whose size and shape can be tailored by changing the solvent nature. We study the complex relationship between wet-chemistry synthesis conditions and resulting layered nanoparticle morphology. Furthermore, high-level electronic structure theory, including dispersion corrections to account for van der Waals forces, is employed to enhance our understanding of the underlying chemical mechanisms. The electronic vacuum alignment and surface energies are determined, allowing the prediction of the thermodynamically favoured crystal shape (Wulff const...

ACS Nano, 2021

The fast development of terahertz technologies demands high-performance electromagnetic interfere... more The fast development of terahertz technologies demands high-performance electromagnetic interference (EMI) shielding materials to create safe electromagnetic environments. Despite tremendous breakthroughs in achieving superb shielding efficiency (SE), conventional shielding materials have high reflectivity and cannot be re-edited or recycled once formed, resulting in detrimental secondary electromagnetic pollution and poor adaptability. Herein, a hydrogel-type shielding material incorporating MXene and poly(acrylic acid) is fabricated through a biomineralization-inspired assembly route. The composite hydrogel exhibits excellent stretchability and recyclability, favorable shape adaptability and adhesiveness, and fast self-healing capability, demonstrating great application flexibility and reliability. More interestingly, the shielding performance of the hydrogel shows absorption-dominated feature due to the combination of the porous structure, moderate conductivity, and internal water-rich environment. High EMI SE of 45.3 dB and broad effective absorption bandwidth (0.2−2.0 THz) with excellent refection loss of 23.2 dB can be simultaneously achieved in an extremely thin hydrogel (0.13 mm). Furthermore, such hydrogel demonstrates sensitive deformation responses and can be used as an on-skin sensor. This work provides not only an alternative strategy for designing next-generation EMI shielding material but also a highly efficient and convenient method for fabricating MXene composite on macroscopic scales.

Advanced Energy Materials, 2020

Increasing the energy density of lithium‐ion batteries requires the discovery of new electrode ma... more Increasing the energy density of lithium‐ion batteries requires the discovery of new electrode materials capable of achieving very high areal capacity. Here, liquid phase exfoliation is used to produce nanosheets of SnP3, a 2D material with extremely high theoretical capacity of 1670 mAh g−1. These nanosheets can be fabricated into solution‐processed thin films for use as lithium storing anodes. To maximize their performance, carbon nanotubes are incorporated into the electrodes to simultaneously enhance conductivity and toughness. As a result, electrodes of thickness >300 µm can be produced, which display active‐mass‐normalized capacities (≈1657 mAh g−1Active) very close to the theoretical value. These materials show maximum specific (≈1250 mAh g−1Electrode) and areal (>20 mAh cm−2) capacities, which are at the state‐of‐the‐art for 2D‐based electrodes, coupled with good rate performance and stability. In combination with commercial cathode materials, full‐cells are fabricated...

Advanced Optical Materials, 2020

Two‐photon absorption (2PA) is a nonlinear optical (NLO) effect that typically occurs in a conven... more Two‐photon absorption (2PA) is a nonlinear optical (NLO) effect that typically occurs in a conventional semiconductor whose bandgap is larger than the energy of one excited photon but smaller than the energy of two photons. In this work, the experimental observation of strong 2PA in gapless MXene monolayers is reported. This phenomenon is verified by a nonlinear transmission method and ultrafast dynamic studies based on a wavelength‐degenerate, non‐collinear pump‐probe technique. The unconventional 2PA is attributed to the structures of the MXene energy bands near the Fermi level, which favors two‐photon transitions and suppresses one‐photon transitions due to parallel band absorption effects. These results, as well as the measured NLO parameters including the 2PA coefficient, absorption cross‐section, excited carrier lifetimes, and third‐order NLO susceptibility, provide a systematic understanding of the unusual NLO effect in MXenes and may be applied in advanced photonic and optoe...

Materials Today, 2019

The consumer demand for flexible wearables has increased rapidly with the advent of recent commer... more The consumer demand for flexible wearables has increased rapidly with the advent of recent commercial health monitoring systems. The progress in wearable electronics for monitoring physiological parameters in the healthcare industry is rapid and its adaptation is having a positive impact on society. Physiological parameters are important health indicators and their monitoring could effectively enable early detection of disease. This would also help reduce the number of more severe health problems, in disease prevention and lower the overall public sector health cost. Clinical devices for measurement of these parameters are also traditionally non-wearable. Therefore, companies and researchers are focused on the development of new materials and related manufacturing methods which will enable specific wearable health sensors with a high degree of robustness, repeatability and accuracy. On the development of printed physiological signal monitoring devices, much progress has been achieved in recent years. Eventhough several reviews have been presented on flexible and wearable electronics, a detailed summary of the recent progresses on the specific class of printed physiological signal monitoring sensing devices has not been reported. In this review, recent progress and challenges on the functional inks and substrate materials for mass scale production and customization of printed flexible and wearable physiological signal monitoring sensor devices are summarized.

Scientific Reports, 2019

Considerable attention has been drawn to the lead halide perovskites (LHPs) because of their outs... more Considerable attention has been drawn to the lead halide perovskites (LHPs) because of their outstanding optoelectronic characteristics. LHP nanosheets (NSs) grown from single crystalline lead halide possess advantages in device applications as they provide the possibility for control over morphology, composition, and crystallinity. Here, free-standing lead bromide (PbBr2) single-crystalline NSs with sizes up to one centimeter are synthesized from solution. These NSs can be converted to LHP while maintaining the NS morphology. We demonstrate that these perovskite NSs can be processed directly for fabrication of photodetector and laser arrays on a large scale. This strategy will allow high-yield synthesis of large-size perovskite NSs for functional devices in an integrated photonics platform.

Applied Physics Letters, 2017

Tailoring the electrical properties of transition metal dichalcogenides by doping is one of the b... more Tailoring the electrical properties of transition metal dichalcogenides by doping is one of the biggest challenges for the application of 2D materials in future electronic devices. Here, we report on a straightforward approach to the n-type doping of molybdenum disulfide (MoS2) films with rhenium (Re). High-Resolution Scanning Transmission Electron Microscopy and Energy-Dispersive X-ray spectroscopy are used to identify Re in interstitial and lattice sites of the MoS2 structure. Hall-effect measurements confirm the electron donating influence of Re in MoS2, while the nominally undoped films exhibit a net p-type doping. Density functional theory (DFT) modelling indicates that Re on Mo sites is the origin of the n-type doping, whereas S-vacancies have a p-type nature, providing an explanation for the p-type behaviour of nominally undoped MoS2 films.

Nature Communications, 2019

One weakness of batteries is the rapid falloff in charge-storage capacity with increasing charge/... more One weakness of batteries is the rapid falloff in charge-storage capacity with increasing charge/discharge rate. Rate performance is related to the timescales associated with charge/ionic motion in both electrode and electrolyte. However, no general fittable model exists to link capacity-rate data to electrode/electrolyte properties. Here we demonstrate an equation which can fit capacity versus rate data, outputting three parameters which fully describe rate performance. Most important is the characteristic time associated with charge/discharge which can be linked by a second equation to physical electrode/electrolyte parameters via various rate-limiting processes. We fit these equations to ~200 data sets, deriving parameters such as diffusion coefficients or electrolyte conductivities. It is possible to show which rate-limiting processes are dominant in a given situation, facilitating rational design and cell optimisation. In addition, this model predicts the upper speed limit for ...

Nature Communications, 2019

Direct printing of functional inks is critical for applications in diverse areas including electr... more Direct printing of functional inks is critical for applications in diverse areas including electrochemical energy storage, smart electronics and healthcare. However, the available printable ink formulations are far from ideal. Either surfactants/additives are typically involved or the ink concentration is low, which add complexity to the manufacturing and compromises the printing resolution. Here, we demonstrate two types of two-dimensional titanium carbide (Ti3C2Tx) MXene inks, aqueous and organic in the absence of any additive or binary-solvent systems, for extrusion printing and inkjet printing, respectively. We show examples of all-MXene-printed structures, such as micro-supercapacitors, conductive tracks and ohmic resistors on untreated plastic and paper substrates, with high printing resolution and spatial uniformity. The volumetric capacitance and energy density of the all-MXene-printed micro-supercapacitors are orders of magnitude greater than existing inkjet/extrusion-print...

Journal of Materials Chemistry A, 2019

Ionogel-based flexible micro-supercapacitors are constructed based on interdigital microelectrode... more Ionogel-based flexible micro-supercapacitors are constructed based on interdigital microelectrodes of ionic liquid pre-intercalated MXene compact films.

ACS Applied Nano Materials, 2018

Carbon nanofoam (CNF) is a low-density, high-surface-area material formed by aggregation of amorp... more Carbon nanofoam (CNF) is a low-density, high-surface-area material formed by aggregation of amorphous carbon nanoparticles into porous nanostructures. We report the use of a pulsed infrared laser to prepare CNF from a graphene oxide (GO) target material. Electron microscopy shows that the films consist of dendritic strings which form web-like three-dimensional structures. The conductivity of these structures can be modified by using the CNF as a nanostructured scaffold for gold nanoparticles deposited by sputter coating, controllably increasing the conductivity by up to four orders of magnitude. The ability to measure the conductivity of the porous structures allows electrochemical measurements in the environment. Upon decreasing humidity, the pristine CNF exhibits an increase in resistance with a quick response and recovery time. By contrast, the goldsputtered CNF showed a decrease in resistance, indicating modification of the doping mechanism due to water adsorption. The sensitivity to humidity is eliminated at the percolation threshold of the metal on the CNF.

Advanced science (Weinheim, Baden-Wurttemberg, Germany), 2018

Sulfur (S) is an attractive cathode material with advantages including high theoretical capacity ... more Sulfur (S) is an attractive cathode material with advantages including high theoretical capacity and low cost. However, issues such as the lithium polysulfide shuttle effect and its insulating properties greatly limit the future applications of lithium-sulfur (Li-S) batteries. Here, a viscous aqueous ink with nanoscale S uniformly decorated on the polar, metallically conductive titanium carbide MXene nanosheets (S@TiCT ) is reported to address these issues. Importantly, it is observed that the conductive TiCT mediator efficiently chemisorbs the soluble polysulfides and converts them into thiosulfate/sulfate. The in situ formed sulfate complex layer acts as a thick protective barrier, which significantly retards the shuttling of polysulfides upon cycling and improves the sulfur utilization. Consequently, the binder-free, robust, highly electrically conductive composite film exhibits outstanding electrochemical performance, including high capacities (1244-1350 mAh g), excellent rate h...

Scientific reports, Jan 8, 2018

This paper describes the wet-chemistry synthesis of highly crystalline hexagonal flakes of Ni-Fe ... more This paper describes the wet-chemistry synthesis of highly crystalline hexagonal flakes of Ni-Fe layered double hydroxide (LDH) produced at temperature as low as 100 °C. The flakes with diameter in the range of 0.5-1.5 μm and the thickness between 15 and 20 nm were obtained by homogeneous precipitation method with the use of triethanolamine (TEA) and urea. By analyzing the intermediate products, it is suggested that, differently from previous reports, a thermodynamically metastable iron oxyhydroxide and Ni-TEA complex are firstly formed at room temperature. Subsequently, when the mixture is heated to 100 °C and the pH increases due to the thermal decomposition of urea, Ni and Fe are slowly released and then recombine, thus leading to formation of pure, highly-crystalline Ni-Fe LDH flakes. This material showed promising results as an electrocatalyst in oxygen evolution reaction (OER) providing an overpotential value of 0.36 V.

npj 2D Materials and Applications, 2017

Titanium (IV) sulphide (TiS2) is a layered transition metal dichalcogenide, which we exfoliate us... more Titanium (IV) sulphide (TiS2) is a layered transition metal dichalcogenide, which we exfoliate using liquid phase exfoliation. TiS2 is a candidate for being part of a range of future technologies. These applications are varied, and include supercapacitor and battery energy storage devices, catalytic substrates and the splitting of water. The driving force behind our interest was as a material for energy storage devices. Here we investigate a potential failure mechanism for such devices, namely oxidation and subsequent loss of sulphur. This degradation is important to understand, since these applications are highly property-dependent, and changes to the chemistry will result in changes in desired properties. Two approaches to study oxidisation were taken: ex situ oxidation by water and oxygen at room temperature and in situ oxidation by a 5% O2/Ar gas at elevated temperatures. Both sources of oxygen resulted in oxidation of the starting TiS2 flakes, with differing morphologies. Water...

Microscopy and Microanalysis, 2015