Fabrication of high-performance MXene-based all-solid-state flexible microsupercapacitor based on a facile scratch method

Intelligent, Flexible Artificial Throats with Sound Emitting, Detecting, and Recognizing Abilities

In recent years, there has been a notable rise in the number of patients afflicted with laryngeal diseases, including cancer, trauma, and other ailments leading to voice loss. Currently, the market is witnessing a pressing demand for medical and healthcare products designed to assist individuals with voice defects, prompting the invention of the artificial throat (AT). This user-friendly device eliminates the need for complex procedures like phonation reconstruction surgery. Therefore, in this review, we will initially give a careful introduction to the intelligent AT, which can act not only as a sound sensor but also as a thin-film sound emitter. Then, the sensing principle to detect sound will be discussed carefully, including capacitive, piezoelectric, electromagnetic, and piezoresistive components employed in the realm of sound sensing. Following this, the development of thermoacoustic theory and different materials made of sound emitters will also be analyzed. After that, various algorithms utilized by the intelligent AT for speech pattern recognition will be reviewed, including some classical algorithms and neural network algorithms. Finally, the outlook, challenge, and conclusion of the intelligent AT will be stated. The intelligent AT presents clear advantages for patients with voice impairments, demonstrating significant social values.

MXene-Based Micro-Supercapacitors: Ink Rheology, Microelectrode Design and Integrated System

MXenes have shown great potential for micro-supercapacitors (MSCs) due to the high metallic conductivity, tunable interlayer spacing and intercalation pseudocapacitance. In particular, the negative surface charge and high hydrophilicity of MXenes make them suitable for various solution processing strategies. Nevertheless, a comprehensive review of solution processing of MXene MSCs has not been conducted. In this review, we present a comprehensive summary of the state-of-the-art of MXene MSCs in terms of ink rheology, microelectrode design and integrated system. The ink formulation and rheological behavior of MXenes for different solution processing strategies, which are essential for high quality printed/coated films, are presented. The effects of MXene and its compounds, 3D electrode structure, and asymmetric design on the electrochemical properties of MXene MSCs are discussed in detail. Equally important, we summarize the integrated system and intelligent applications of MXene MSCs and present the current challenges and prospects for the development of high-performance MXene MSCs.

Constructing MXene-PANI@MWCNTs heterojunction with high specific capacitance towards flexible micro-supercapacitor

Micro-supercapacitors (MSCs) are considered as the promising energy supply of miniaturized electronic devices. The electrode material, as one integral part, play a crucial role on the energy storage performance of MSCs. In our work, we constructed a heterojunction in MXene-PANI@MWCNTs (MPM) ternary composite, benefitting for the synergistic enhancement effect among MXene, polyaniline (PANI) and multiwall carbon nanotubes, an outstanding specific capacitance of 414 F g^-1(at 1 A g^-1) has been achieved. MPM shows high capacitance retention at large current density (86.7%, at 10 A g^-1) and long-term cycling stability of 90.4% for 10 000 cycles. Furthermore, we obtained MPM self-standing films, and constructed a flexible all-solid-state MSC based on the film electrode. A competitive charge storage capability of 30.2 mF cm^-2and long-term stability of 70.2% retention for 10 000 cycles was obtained in the MSC. Meanwhile, the MSC shows excellent flexibility, maintaining most capacitance under bending conditions. Moreover, using an integrated strategy, MSCs can obtain tunable voltages and currents that meet various practical requirements. All these results indicate that the MPM is an excellent charge storage material and will become a potential candidate for flexible energy-storage devices.

Progress and Perspectives in Designing Flexible Microsupercapacitors

Miniaturized flexible microsupercapacitors (MSCs) that can be integrated into self-powered sensing systems, detecting networks, and implantable devices have shown great potential to perfect the stand-alone functional units owing to the robust security, continuously improved energy density, inherence high power density, and long service life. This review summarizes the recent progress made in the development of flexible MSCs and their application in integrated wearable electronics. To meet requirements for the scalable fabrication, minimization design, and easy integration of the flexible MSC, the typical assembled technologies consist of ink printing, photolithography, screen printing, laser etching, etc., are provided. Then the guidelines regarding the electrochemical performance improvement of the flexible MSC by materials design, devices construction, and electrolyte optimization are considered. The integrated prototypes of flexible MSC-powered systems, such as self-driven photodetection systems, wearable sweat monitoring units are also discussed. Finally, the future challenges and perspectives of flexible MSC are envisioned.

Cobalt Oxide-Decorated Silicon Carbide Nano-Tree Array Electrode for Micro-Supercapacitor Application

A cobalt oxide (Co₃O₄)-decorated silicon carbide (SiC) nano-tree array (denoted as Co₃O₄/SiC NTA) electrode is synthesized, and it is investigated for use in micro-supercapacitor applications. Firstly, the well-standing SiC nanowires (NWs) are prepared by nickel (Ni)-catalyzed chemical vapor deposition (CVD) method, and then the thin layer of Co₃O₄ and the hierarchical Co₃O₄ nano-flower-clusters are, respectively, fabricated on the side-walls and the top side of the SiC NWs via electrodeposition. The deposition of Co₃O₄ on the SiC NWs benefits the charge transfer at the electrode/aqueous electrolyte interface due to its extremely hydrophilic surface characteristic after Co₃O₄ decoration. Furthermore, the Co₃O₄/SiC NTA electrode provides a directional charge transport route along the length of SiC nanowires owing to their well-standing architecture. By using the Co₃O₄/SiC NTA electrode for micro-supercapacitor application, the areal capacitance obtained from cyclic voltammetry measurement reaches 845 mF cm⁻² at a 10 mV s⁻¹ scan rate. Finally, the capacitance durability is also evaluated by the cycling test of cyclic voltammetry at a high scan rate of 150 mV s⁻¹ for 2000 cycles, exhibiting excellent stability.

Silicon-Based 3D All-Solid-State Micro-Supercapacitor with Superior Performance

The large-scale fabrication of high-performance on-chip micro-supercapacitors (MSCs) is the footstone for the development of next-generation miniaturized electronic devices. In practical applications, however, MSCs may suffer from a low areal energy density as well as a complicated fabrication strategy that is incompatible with semiconductor processing technology. Herein, we propose a scalable fabrication strategy for the realization of a silicon-based three-dimensional (3D) all-solid-state MSC via the combination of semiconductor-based electrode processing, chemical vapor deposition, and hydrothermal growth. The individual Si/C/MnO₂ electrode shows a maximum specific capacitance of 223.74 mF cm^-2, while the symmetric electrodes present a maximum areal energy density of 5.01 μWh cm^-2 at the scan rate of 1 mV s^-1. The full 3D Si/C/MnO₂ MSC delivers a high energy density of 2.62 μWh cm^-2, at a power density of 117.82 μW cm^-2, as well as a long cycle life with capacitance retention >92% after 4000 cycles. Our proposed method enables the fabrication of 3D MSCs based on a thick silicon interdigitated electrode array, holding a great promise for the development of 3D on-chip microscale energy storage devices.

Boosting Sodium Storage in Two-Dimensional Phosphorene/Ti3C2Tx MXene Nanoarchitectures with Stable Fluorinated Interphase

The stacking of complementary two-dimensional (2D) materials into hybrid architectures is desirable for batteries with enhanced capacity, fast charging, and long lifetime. However, the 2D heterostructures for energy storage are still underdeveloped, and some associated problems like low Coulombic efficiencies need to be tackled. Herein, we reported a phosphorene/MXene hybrid anode with an in situ formed fluorinated interphase for stable and fast sodium storage. The combination of phosphorene nanosheets with Ti₃C₂T_x MXene not only facilitates the migration of both electrons and sodium cations but also alleviates structural expansion of phosphorene and thereby improves the cycling performance of the hybrid anode. X-ray photoelectron spectroscopy in-depth analysis reveals that the fluorine terminated MXene stabilize the solid electrolyte interphase by forming fluorine-rich compounds on the anode surface. Density functional theory calculations confirm that the sodium affinities and diffusion kinetics are significantly enhanced in the phosphorene/MXene heterostructure, particularly in the phosphorene/Ti₃C₂F₂. As a result, the hybrid electrode achieved a high reversible capacity of 535 mAh g^-1 at 0.1 A g^-1 and superior cycling performance (343 mAh g^-1 after 1000 cycles at 1 A g^-1 with a capacity retention of 87%) in a fluorine-free carbonate electrolyte.

Progress of Two-Dimensional Ti3 C2 Tx in Supercapacitors

Exploring stable cycling electrode materials with high energy and power density is the key to accelerating the development and application of supercapacitors. Ti₃ C₂ T_x , which is the most investigated member of the family of two-dimensional layered transition-metal carbides, has attracted considerable attention, owing to its unique two-dimensional morphology, large interlayer spacing, outstanding metallic conductivity, abundant chemical surface, and ultrahigh volumetric capacitance. However, the inherent restacking tendency of ultrathin Ti₃ C₂ T_x sheets hinder its practical application. In this review, the synthetic methods and charge-storage mechanisms of Ti₃ C₂ T_x are stressed to provide clues for improving its electrochemical performance. Functionalization, including architectural construction, hybridization, and surface modification of the Ti₃ C₂ T_x sheets, to circumvent difficulties and application in supercapacitors is then summarized. Accordingly, the aim is to highlight the opportunities and challenges for Ti₃ C₂ T_x -based materials in practical applications in supercapacitors.

Emerging 2D MXenes for supercapacitors: status, challenges and prospects

This review provides a comprehensive understanding of the emerging 2D MXene electrode materials for supercapacitor application.

Layered coating of ultraflexible graphene-based electrodes for high-performance in-plane quasi-solid-state micro-supercapacitors

To meet the demand of rapid development of portable and wearable electronic devices, in-plane quasi-solid-state micro-supercapacitors (QSS MSCs) have great potential as miniaturized energy storage devices. However, their ultralow areal capacitance and poor flexibility limit their practical applications. Here, we demonstrate a new strategy for the fabrication of ultraflexible MnO2@reduced graphene oxide (rGO) films (MGFs) for high-performance planar QSS MSCs through a facile layer-by-layer coating and a laser engraving method. Benefiting from conductive and flexible rGO films reduced by HI, the MGF based symmetrical QSS MSC exhibits a high areal capacitance (31.5 mF cm-2 at 0.2 mA cm-2), excellent flexibility (no capacity degradation at a bending radius from ∞ to 0 cm), and outstanding cycling stability (retaining 77.0% of its initial capacity after 6000 cycles). Most importantly, the electrochemical performance of QSS MSCs can be multiplied by simply adding more MGF layers. By adding up to 5 MGF layers, the MSC can deliver an ultrahigh areal capacitance of 144.3 mF cm-2 at 0.3 mA cm-2, and a superior energy density of 13.9 mW h cm-3 at 34.7 mW cm-3. Therefore, this work offers versatile quasi-solid-state MSCs and provides an impressive strategy to enhance electrochemical performance which will greatly enrich the design and fabrication of MSCs.

Structural Engineering of Low-Dimensional Metal-Organic Frameworks: Synthesis, Properties, and Applications

Low-dimensional metal-organic frameworks (LD MOFs) have attracted increasing attention in recent years, which successfully combine the unique properties of MOFs, e.g., large surface area, tailorable structure, and uniform cavity, with the distinctive physical and chemical properties of LD nanomaterials, e.g., high aspect ratio, abundant accessible active sites, and flexibility. Significant progress has been made in the morphological and structural regulation of LD MOFs in recent years. It is still of great significance to further explore the synthetic principles and dimensional-dependent properties of LD MOFs. In this review, recent progress in the synthesis of LD MOF-based materials and their applications are summarized, with an emphasis on the distinctive advantages of LD MOFs over their bulk counterparties. First, the unique physical and chemical properties of LD MOF-based materials are briefly introduced. Synthetic strategies of various LD MOFs, including 1D MOFs, 2D MOFs, and LD MOF-based composites, as well as their derivatives, are then summarized. Furthermore, the potential applications of LD MOF-based materials in catalysis, energy storage, gas adsorption and separation, and sensing are introduced. Finally, challenges and opportunities of this fascinating research field are proposed.

Recent advances in micro-supercapacitors

Micro-supercapacitors (MSCs) possessing the remarkable features of high electrochemical performance and relatively small volume are promising candidates for energy storage in micro-devices. Tremendous effort has been devoted in recent years to design and to fabricate MSCs with different active electrode materials, including carbon-based materials, conducting polymers, and graphene/metal oxide composites. Moreover, various methods have been developed to prepare MSCs, such as photolithography, laser direct writing, printing methods. This review presents a summary of the recent developments in MSC technology, including electrode materials, fabrication methods, and patterning. Finally, future developments, perspectives, and challenges in the MSC industry are also discussed.

Flexible Ti3C2Tx/PEDOT:PSS films with outstanding volumetric capacitance for asymmetric supercapacitors

MXenes are two-dimensional transition metal carbides/nitrides, and they have shown exciting application prospects for electrochemical energy storage in the future owing to their hydrophilicity, metallic conductivity and surface redox reactions, which are crucial for high-capacitance and high-rate electrode materials. However, the strong tendency of adjacent MXene flakes to aggregate or self-restack under the van der Waals force limits the electrochemical performance of MXene-based electrodes for practical applications. In this study, we developed a simple and effective method to prepare Ti₃C₂T_x/PEDOT:PSS hybrid films via filtering the Ti₃C₂T_x/Clevios PH1000 compound inks, followed by H₂SO₄ treatment. H₂SO₄ treatment could remove part of the insulating PSS from the Ti₃C₂T_x/PEDOT:PSS hybrid film, resulting in significant conductivity enhancement of the composite. Furthermore, the conductive PEDOT not only acted as a pillar between Ti₃C₂T_x sheets to expose more electroactive surfaces and reduce ion diffusion pathways but also played a role as a conductive bridge to form multidimensional electronic transport channels for accelerating the electrochemical reaction process. As a result, the as-prepared H₂SO₄-treated Ti₃C₂T_x/PEDOT:PSS (Ti₃C₂T_x/P-100-H) hybrid film exhibited 4.5-fold increase in the specific surface area and high volumetric capacitance of 1065 F cm^-3 at 2 mV s^-1 with superior rate performance in 1 M H₂SO₄ electrolyte. Especially, we assembled an asymmetric supercapacitor (ASC) with excellent flexibility based on a Ti₃C₂T_x/P-100-H hybrid negative electrode and rGO film positive electrode, which delivered high energy density of 23 mW h cm^-3 and high power density of 7659 mW cm^-3. Moreover, a simple luminous band was designed and powered by our two ASCs in series. The outstanding volumetric electrochemical performance and energy density of the ASC based on the flexible Ti₃C₂T_x/P-100-H hybrid film electrode demonstrated its promising potential as a strong power source for small portable and wearable electronic devices.

Applications of 2D MXenes in energy conversion and storage systems

This article provides a comprehensive review of MXene materials and their energy-related applications.

Plasma-Assisted Synthesis of NiSe2 Ultrathin Porous Nanosheets with Selenium Vacancies for Supercapacitor

Two-dimensional (2D) NiSe₂ nanosheets with porous ultrathin structure and selenium vacancies (NiSe₂ PNS_vac) are synthesized via plasma-assisted dry exfoliation for supercapacitor. The specific capacitance of the NiSe₂ PNS_vac is 466 F g^-1 in 1 M KOH electrolyte, which is much higher than those of NiSe₂ ultrathin nanosheeets (328 F g^-1) and NiSe₂ particles (251 F g^-1). After 1000 cycles, the specific capacitance of the NiSe₂ PNS_vac can be well-maintained, indicating its high cycling stability. The superior performance arose from its high conductivity, short electrolyte diffusion distance, and large specific surface area.