Turning Trash into Treasure: Additive Free MXene Sediment Inks for Screen-Printed Micro-Supercapacitors

Non-enzymatic electrochemical sensors for point-of-care testing: Current status, challenges, and future prospects

Current electrochemical sensors in point-of-care (POC) testing devices rely mainly on enzyme-based sensors owing to superior sensitivity and selectivity. Nevertheless, the poor stability, high reagent cost, complex fabrication methods and requirement of specific operational conditions make their adaptability in real-world applications unfavorable. Non-enzymatic electrochemical sensors are thus developed as they are more robust and cost-effective strategies. The advancement in material science and nanotechnology enables the development of novel non-enzymatic electrodes with favorable analytical performance. However, the developments are yet far from being adopted as viable products. This review therefore aims to gain insight into the field and evaluate the current progress and challenges to eventually propose future research directions. Here, fabrication strategies based on traditional and emerging technology are discussed in the light of analytical performance and cost-effectiveness. Moreover, the discussion is given on the pros and cons of non-enzymatic sensors when they are employed with various kinds of sample matrices, i.e., clinical and non-clinical samples, which must be taken into consideration for sensor development. Furthermore, molecular imprinting technology in tackling the selectivity issue is introduced and current progress is provided. Finally, the promising strategies from literature for solving the remaining challenges are included which could facilitate further development of robust POC testing devices based non-enzymatic sensors. We believe that once researchers and technology developers have reached the point where most problems are solved, the non-enzymatic sensors are going to be the robust choice for POC testing in clinical diagnostic, ensuring food safety, monitoring contaminants in environment, and bioprocess control.

MXene/Carboxylated Cellulose Nanofiber Inks for Direct Ink Writing Electromagnetic Interference Shielding, Humidity Sensing, and Joule Heating

Two-dimensional transition metal carbide/nitride (MXene)-based conductive inks are promising in the scalable production of printed electronics and wearable devices. Nevertheless, to realize desirable rheological properties of MXene-based inks and the multifunction of the resulting printed devices is still challenging. Herein, MXene inks with tunable rheological properties were developed by inducing carboxylated cellulose nanofibers (C-CNFs) modifier. The versatile rheological properties of MXene inks facilitate the preparation of MXene gratings by direct ink writing (DIW) and multifunctional devices integrated with electromagnetic interference (EMI) shielding, Joule heaters, and humidity sensors. The highest average EMI shielding effectiveness (SE) is 33.0 dB, with specific EMI SE up to 137481.5 dB cm2 g-1. Meanwhile, when functioning as a Joule heater, a low-voltage drive and excellent cyclic and long-term stability can be observed. In addition, the humidity-sensing function integrated with wireless transmission shows a maximum response value of 2768%. The MXene gratings fabricated by DIW are multifunctional and can be applied to the next generation of wearable devices.

Interwoven MXene Sediment Architecture Empowers High-Performance Flexible Microwave Devices

Flexible microwave devices are critical in wearable electronic systems for wireless communication, where highly conductive materials are essential to ensure optimal electromagnetic performance. Titanium carbide (MXene), renowned for its excellent conductivity, lightweight, and easy fabrication, emerges as a promising alternative to conventional metal materials in wearable electronics. However, the technical limitation of MXene suspensions or sediments in fabricating high-performance microwave devices with low cost and scalable production present a huge challenge for their practical applications. Herein, an interwoven MXene sediment architecture is designed on natural cross-linked textiles, achieving high material yield and superior conductivity simultaneously. The architecture breaks up the planar conductive behavior of conventional stacked MXene films, facilitating multi-directional electron transport and pushing the conductivity of MXene sediment microwave devices up to 1.6 × 106 S m-1. The underlying mechanisms responsible for the improvement in conductivity are investigated using resistor network models and percolation theory. Moreover, the architecture demonstrates high performance in electromagnetic interference shielding, and supports high-quality and long-range wireless communications. This validation not only underscores the effectiveness of the interwoven MXene sediment architecture, but also establishes the MXene-based microwave devices as a transformative component for the next generation of high-performance flexible wireless communication technologies.

Recent development review of Ti3C2Tx MXene-based microsupercapacitors: a multi-dimensional analysis spanning from underlying mechanisms to integrated applications

Microsupercapacitors, as innovative energy storage devices, have garnered significant attention in microelectronics and wearable applications. The urgent demand to enhance the charge storage capacity and operational efficiency of MSCs, coupled with challenges such as limited charge-active sites and low ion transport efficiency, has driven continuous optimization of their constituent materials and structural designs. The emerging two-dimensional MXenes, with their rich surface chemical functionalities, tunable interlayer spacing, and excellent compatibility with various nanomaterials, offer unprecedented opportunities for MSCs. However, current analyses of how MXenes enhance the performance of MSCs from the energy storage mechanism perspective, their multiple applications in MSCs, and the system-level integration of MSCs are incomplete, limiting the development of this field. Herein, this review presents a comprehensive overview of the latest advancements in the energy storage mechanisms and fabrication techniques of Ti3C2Tx-based MSCs, especially emphasizes their applications across various components of MSCs, and provides a detailed summary of integrated examples of MSC-powered systems. This work offers an in-depth analysis of the key role of Ti3C2Tx in enhancing the performance of MSCs, as well as outlines the challenges and prospects for its forthcoming research, with the potential to drive continued innovation in high-performance flexible energy storage devices.

Laser Patterned In-Plane Asymmetric MXene//LIG@MnO Microsupercapacitor for Self-Powered Pressure Detection Systems

Wearable and portable microelectronic devices are attracting growing attention in the scientific and technological fields. The preparation of high-performance micro energy storage devices in self-sustaining flexible electronic systems still needs further studies. In this work, we have developed a preparation method for asymmetric microsupercapacitors (AMSCs). The MnO cathodes are fabricated by laser irradiation, which converts manganese acetate into manganese oxide on the hydrophilic laser-induced graphene interdigitated electrodes. By controlling the number of drop-coating cycles of the manganese acetate solution, precise control over MnO loading is achieved. We investigated the impacts of laser power and scanning direction on the phase and performance of the MnO cathodes, establishing the optimal laser processing parameters. The MXene//MnOAMSC after capacity matching demonstrates excellent rate performance (maintaining 82% even at 10 times the current density of 0.1 mA cm-2), outstanding mechanical flexibility, and long-term cycling stability (90% capacitance retention after 10,000 cycles). Furthermore, by serially connecting a solar cell, an AMSC, and pressure-sensitive elements, a self-powered pressure detection system is constructed. This integrated system exhibits a clear current response to finger bending, elbow bending, and finger touch.

GO-Enhanced MXene Sediment-Based Inks Achieve Remarkable Oxidation Resistance and High Conductivity

MXenes are emerging materials renowned for their exceptional conductivity, abundant functional groups, and excellent solution processability, making them highly promising as conductive-additive-free inks for flexible electronic devices. However, current preparation methods are hampered by low yields of MXene flakes so that substantial waste MXene sediments (MS) are generated. Here, we demonstrate a type of conductive ink with appropriate rheological properties, namely MG inks formulated using MS and graphene oxide (GO), for screen-printing frequency selective surface (FSS). GO facilitates interlayer interactions by covalently cross-linking with MXene flakes, resulting in a denser structure and significantly enhancing the conductivity of the best-performing MG-based ink to 849 S cm-1. Additionally, GO serves as a binder to considerably improve the rheological properties of MS, thus enabling high-quality printing on various substrates. The close stacking of MS and GO not only improves the oxidation resistance but also maintains conductivity above 97% even after 60 days. Furthermore, the MG-based FSS produced via straightforward screen printing demonstrates excellent performance and retains its functionality after 90 days of operation. This MS-based ink formulation represents a strategy of "turning trash into treasure" and highlights the potential of MS for the next generation of electronic devices.

An ultrastretchable seamlessly integrated contactless charging microsystem towards skin-attachable wireless microelectronics

For electronics to be wearable, contactless charging and overall deformability are necessary pre-conditions. However, the current heterogeneous integration based on different active materials and separate manufacturing often leads to mechanical mismatch. Here, we report an ultrastretchable all-in-one integrated MXene-based microsystem comprising wireless coils, micro-supercapacitors (MSCs) and strain sensors. The seamless configuration without any connecting interface dramatically improves the structural integrity of the microsystem, and a pre-crumpled structure endows it with superior stretchability. Attributed to these, our MSCs can be wirelessly charged in ~20 s under various types of deformation and are capable of powering strain sensors, responding rapidly to body motion signals. Moreover, the MSCs display a high specific capacitance of 76.82 F cm-3, and superb mechanical stability with 98.5% capacitance retention after biaxial stretching 1000 cycles from 0% to 500% areal strain. Therefore, this work sheds new insights into design and implementation of skin-attachable wireless microelectronics.

Recent Advances in MXene-Based Electrochemical Sensors

MXene is a new family of two-dimensional nanomaterials with outstanding electrical conductivity, tunable structure, biocompatibility, and a large surface area. Thanks to these unique physicochemical properties, MXene has been used for constructing electrochemical sensors (MECSens) with excellent performance. In particular, the abundant surface termination of MXene can contribute to greatly enhancing the analytical sensitivity and selectivity of MECSens. Recently, MECSens have been widely applied in many fields including clinical diagnosis, infectious disease surveillance, and food security. However, not all MXene materials are suitable for building electrochemical sensors. In this article, we present an overview of different MECSens that have been developed so far. We begin with a short summary of the preparation and characterization of MECSens. Subsequently, the electrochemical performance, detection strategies, and application scenarios of MECSens are classified and briefly discussed. The article ends with a short conclusion and future perspectives. We hope this article will be helpful for designing and constructing MECSens with outstanding activity for electrochemical analysis.

Advancements in 2D Titanium Carbide (MXene) for Electromagnetic Wave Absorption: Mechanisms, Methods, Enhancements, and Applications

With the advent of the 5G era, there has been a marked increase in research interest concerning electromagnetic wave-absorbing materials. A critical challenge remains in improving the wave-absorbing properties of these materials while satisfying diverse application demands. MXenes, identified as prominent "emerging" 2D materials for wave absorption, offer unique advantages that are expected to drive advancements and innovations in this field. This review emphasizes the synthesis benefits provided by the unique structural characteristics of MXenes and the performance enhancements achieved through their combination with other absorbing materials. Material requirements, synthesis approaches, and conceptual frameworks are integrated to underscore these advantages. The study provides a thorough analysis of MXene-absorbing composites, going beyond basic classification to address preparation and modification processes affecting the absorption properties of MXenes and their composites. Attention is directed to synthesis techniques, structural design principles, and their influence on composite performance. Additionally, the potential applications of MXenes in electromagnetic wave absorbing devices are summarized. The review concludes by addressing the challenges currently confronting MXene materials and outlining expected developmental trends, aiming to offer guidance for subsequent research in this domain.

Tailored Nanoarchitectures: MoS₂/Graphene and MoS2/Graphene Oxide Thin Films via Liquid-Liquid Interfacial Route

The nanostructured assembly of different two-dimensional (2D) materials in specific organization is crucial for developing materials with synergistic properties. In this study, we present a general methodology to prepare thin, transparent and self-assembled films of 2D/2D composites based on molybdenum sulfide (MoS2)/graphene oxide (GO) or MoS2/reduced graphene oxide (rGO), through the liquid/liquid interfacial route. Different nanoarchitectures are obtained by changing simple experimental parameters during the thin film preparation steps. The films were characterized by UV-Vis and Raman spectroscopy, scanning electron microscopy and cyclic voltammetry, evidencing that the experimental route used plays a role in the organization and properties of the assembled nanoarchitectures. Likewise, nanostructures of MoS2/GO and MoS2/rGO prepared through the same route have different organizations due to the different interactions between the materials. This showcases the potential of the technique to prepare tailored nanoarchitectures with specific properties for various applications, paving the way for innovative nanotechnology and materials science applications.

In-situ construction of integrated asymmetric micro-supercapacitors achieving monolithic hundred-volt output

Asymmetric micro-supercapacitors (MSCs) exhibit higher energy density while face significant challenges in power density as well as cycling life and large dimensions. The key factors contributing to these dilemmas include the match of electrode materials and electrolytes, poor uniformity of device, and complicated while low-precise fabrication processes. Herein we develop a laser scribing-engraving (LSE) strategy to fabricate MSCs with monolithic high-voltage output and scalable array integration. Utilizing this strategy, we induce the conversion of the majority of Ti3C2Tx-MXene into TiO2 and graphene oxide into laser-scribed graphene (LSG), yielding asymmetric MSCs with laser-induced MXene/graphene oxide as the negative electrode and MXene/graphene oxide as the positive electrode. A single asymmetric micro-supercapacitor exhibits a high voltage window of 1.8 V, delivering an outstanding energy density (240 mWh cm-3) and power density (9503 mW cm-3), coupled with excellent cycling stability. Moreover, the LSE strategy enables monolithically integrated 64 devices to achieve a high-voltage output of 115.2 V. Our approach showcases the potential for integrating micro-energy storage devices into various microsystems, increasing the practicality of asymmetric micro-supercapacitors.

Design and Fabrication of MoCuOx Bimetallic Oxide Electrodes for High-Performance Micro-Supercapacitor by Electro-Spark Machining

Transition metal oxides, distinguished by their high theoretical specific capacitance values, inexpensive cost, and low toxicity, have been extensively utilized as electrode materials for high-performance supercapacitors. Nevertheless, their conductivity is generally insufficient to facilitate rapid electron transport at high rates. Therefore, research on bimetallic oxide electrode materials has become a hot spot, especially in the field of micro-supercapacitors (MSC). Hence, this study presents the preparation of bimetallic oxide electrode materials via electro-spark machining (EM), which is efficient, convenient, green and non-polluting, as well as customizable. The fabricated copper-molybdenum bimetallic oxide (MoCuOx) device showed good electrochemical performance under the electrode system. It provided a high areal capacity of 50.2 mF cm-2 (scan rate: 2 mV s-1) with outstanding cycling retention of 94.9% even after 2000 cycles. This work opens a new window for fabricating bimetallic oxide materials in an efficient, environmental and customizable way for various electronics applications.

Enhanced Oxidation-Resistant and Conductivity in MXene Films with Seamless Heterostructure

MXene-based films have garnered significant attention for their remarkable electrical and mechanical properties. Nevertheless, the practical application of MXene is impeded by its intrinsic instability caused by spontaneous oxidation. The traditional anti-oxidative strategies frequently lead to a compromise in stability, electrical conductivity, and mechanical properties. In this study, a novel approach is proposed involving metal nano-armoring, wherein a copper layer with nano thickness is deposited onto MXene film surfaces to establish a uniform and seamless heterogeneous interface (MXene@Cu). The precise tunability and uniformity of this heterostructure are consistently demonstrated through both theoretical calculations and experimental results. The MXene@Cu films exhibit exceptional electrical conductivity of 1.17 × 106 S m-1, electromagnetic interference shielding effectiveness of 77.1 dB, and tensile strength of 43.4 MPa. More importantly, this heterostructure significantly improves MXene's stability against oxidation. After exposure to air for 30 days, the resultant MXene@Cu films exhibit a remarkable conductivity retention of 72.0%, significantly exceeding that of pristine MXene films (44.3%). This scalable synthesis approach holds significant promise for electronic device applications, particularly in electromagnetic shielding and thermal management.

Electrochemical Performance of Niobium MXenes with Lanthanum

MXenes are the newest class of two-dimensional nanomaterials characterized by large surface area, high conductivity, and hydrophilicity. To further improve their performance for use in energy storage devices, heteroatoms or functional groups can be inserted into the Mxenes' structure increasing their stability. This work proposes insertion of lanthanum atoms into niobium-MXene (Nb-MX/La) that was characterized in terms of morphogy, structure, and electrochemical behavior. The addition of La to the Nb-MXene structure was essential to increase the spacing between the layers, improving the interaction with the electrolyte and enabling charge/discharge cycling in a higher potential window and at higher current densities. Nb-MX/La achieved a specific capacitance of up to 157 mF cm-2, a specific capacity of 42 mAh cm-2 at 250 mV s-1, a specific power of 37.5 mW cm-2, and a specific energy of 14.1 mWh cm-2 after 1000 charge/discharge cycles at 50 mA cm-2.

High Areal Capacitance and Rate Capability of 3D-Printed Thick Electrodes with Optimized Conductive Networks from the Core-Sheath Structure

Material extrusion 3D printing has received enormous attention to potentially overcome its limits by tailoring and designing thick electrodes. In this work, we prepared a thick reduced graphene oxide/carbon nanotube-reduced graphene oxide/carbon nanotubes/manganese oxide@carbon nanotubes (rGC-rGCMC) electrode with controlled lattice architectures, core-sheath structure, and hierarchical porosity by material coaxial extrusion 3D printing, freeze-drying, and thermal treatment. The volume ratios of core to sheath, including 100%-0%, 0%-100%, 20%-80%, 30%-70%, 40%-60%, and 50%-50%, were designed to investigate the influences of the core-sheath structure on thick electrodes. The electrodes with a core-sheath volume ratio of 30%-70% electrodes exhibited an enhanced areal specific capacitance of 588.27 mF cm-2 (39.48 F g-1) at a scan rate of 0.5 mA cm-2. All capacitance decays from core-sheath electrodes (20%-80%, 30%-70%, 40%-60%, and 50%-50%) were smaller than those from rGCMC (0%-100%) electrodes, indicating the improved rate capability from the core-sheath structure. On comparison of 30%-70% core-sheath electrodes with electrodes made of a homogeneous 30% rGC and 70% rGCMC mixture (30%+70%), lower capacitance (382.27 mF cm-2 and 25.66 F g-1 at 0.5 mA cm-2) of the 30%+70% mixture electrode without a core-sheath structure suggested less efficiency to harvest electrons from the redox reactions. Electrochemical impedance spectroscopy (EIS) data further supported and explained the resistances of thick electrodes with different volume ratios.

Unlocking Maximum Synergy: Screen-Printing Fabrication of Heterostructured Microsupercapacitor Stacks

A cost-effective and scalable approach for the fabrication of heterostructured microsupercapacitors (MSCs) employing screen-printing followed by sequential electrochemical and microspray deposition techniques has been demonstrated. The microsupercapacitor electrode (MSC) that composed of stacked layers of mesoporous carbon, polyaniline (PANI), and MXene hold significant promise for wearable electronics. By adjusting the deposition and spray cycles, the MSC can be readily coated with PANI and MXene. The sequentially stacked two layers of MXene and PANI on the mesoporous carbon spheres (PMPM-MSC) yielded a specific capacitance of 1003 mF cm-2 at 0.5 mA cm-2, surpassing the performance of PANI/mesoporous carbon electrode by 1.6 times (771 mF cm-2). After 10,000 cycles of charge and discharge, PMPM-MSCs retained more than 86% of their initial capacitance. In-situ Raman spectroscopy confirmed the synergistic effects between MXene and PANI within the heterostructured stacked PMPM-MSC electrodes, including enhanced electronic conductivity and improved electrolyte ion dissociation, which aligned with the electrochemical measurement results, such as fast charge/discharge rates and reduced internal and mass transport resistance. This study demonstrates the potential of screen-printed heterostructured MSC stacks with maximum electrochemical synergy for portable and wearable energy storage devices.

Unlocking Ultrahigh Initial Coulombic Efficiency of MXene Anode via Presodiation and Electrolyte Optimization

The low initial Coulombic efficiency (ICE) greatly hinders the practical application of MXenes in sodium-ion batteries. Herein, theoretical calculations confirm that -F and -OH terminations as well as the tetramethylammonium ion (TMA+) intercalator in sediment Ti3C2Tx (s-Ti3C2Tx) MXene possess strong interaction with Na+, which impedes Na+ desorption during the charging process and results in low ICE. Consequently, Na+-intercalated sediment Ti3C2Tx (Na-s-Ti3C2Tx) is constructed through Na2S·9H2O treatment of s-Ti3C2Tx. Specifically, Na+ can first exchange with TMA+ of s-Ti3C2Tx and then combine with -F and -OH terminations, thus leading to the elimination of TMA+ and preshielding of -F and -OH. As expected, the resulting Na-s-Ti3C2Tx anode delivers considerably boosted ICE values of around 71% in carbonate-based electrolytes relative to s-Ti3C2Tx. Furthermore, electrolyte optimization is employed to improve ICE, and the results demonstrate that an ultrahigh ICE value of 94.0% is obtained for Na-s-Ti3C2Tx in the NaPF6-diglyme electrolyte. More importantly, Na-s-Ti3C2Tx exhibits a lower Na+ migration barrier and higher electronic conductivity compared with s-Ti3C2Tx based on theoretical calculations. In addition, the cyclic stability and rate performance of the Na-s-Ti3C2Tx anode in various electrolytes are comprehensively explored. The presented simple strategy in boosting ICE significantly enhances the commercialization prospect of MXenes in advanced batteries.

Multi-MXene assisted large-scale manufacturing of electrochemical biosensors based on enzyme-nanoflower enhanced electrodes for the detection of H2O2 secreted from live cancer cells

In situ monitoring of H2O2 in cellular microenvironments plays a critical role in the early diagnosis and pretreatment of cancer, but is limited by the lack of efficient and low-cost strategies for the large-scale preparation of real-time biosensors. Herein, a universal strategy for MXene-based composite inks combined with a scalable screen-printing process is validated in large-scale manufacturing of electrochemical biosensors for in situ detection of H2O2 secreted from live cells. Compositing biocompatible carboxymethyl cellulose (CMCS) with excellent conductive MXene, a water-based ink electrode (MXene/CMCS) with tunable viscosity is efficiently printed with desirable printing accuracy. Subsequently, the MXene/CMCS@HRP electrochemical biosensor exhibits stable electrochemical performance through HRP nanoflower modification, showing rapid electron transport and high electrocatalytic capacity, and demonstrating a low limit of detection (0.29 μM) with a wide linear detection range (0.5 μM-3 mM), superior sensitivity (56.45 μA mM-1 cm-2), long-term stability and high anti-interference ability. Moreover, this electrochemical biosensor is effectively employed for in situ detection of H2O2 secreted from HeLa cells, revealing good biocompatibility and outstanding biosensing capability. This proposed strategy not only extends the possibility of low-cost biomedical devices, but also provides a promising approach for early diagnosis and treatment of cancer.

The Latest Advances in Ink-Based Nanogenerators: From Materials to Applications

Nanogenerators possess the capability to harvest faint energy from the environment. Among them, thermoelectric (TE), triboelectric, piezoelectric (PE), and moisture-enabled nanogenerators represent promising approaches to micro-nano energy collection. These nanogenerators have seen considerable progress in material optimization and structural design. Printing technology has facilitated the large-scale manufacturing of nanogenerators. Although inks can be compatible with most traditional functional materials, this inevitably leads to a decrease in the electrical performance of the materials, necessitating control over the rheological properties of the inks. Furthermore, printing technology offers increased structural design flexibility. This review provides a comprehensive framework for ink-based nanogenerators, encompassing ink material optimization and device structural design, including improvements in ink performance, control of rheological properties, and efficient energy harvesting structures. Additionally, it highlights ink-based nanogenerators that incorporate textile technology and hybrid energy technologies, reviewing their latest advancements in energy collection and self-powered sensing. The discussion also addresses the main challenges faced and future directions for development.

Ultrafast Metal-Free Microsupercapacitor Arrays Directly Store Instantaneous High-Voltage Electricity from Mechanical Energy Harvesters

Harvesting renewable mechanical energy is envisioned as a promising and sustainable way for power generation. Many recent mechanical energy harvesters are able to produce instantaneous (pulsed) electricity with a high peak voltage of over 100 V. However, directly storing such irregular high-voltage pulse electricity remains a great challenge. The use of extra power management components can boost storage efficiency but increase system complexity. Here utilizing the conducting polymer PEDOT:PSS, high-rate metal-free micro-supercapacitor (MSC) arrays are successfully fabricated for direct high-efficiency storage of high-voltage pulse electricity. Within an area of 2.4 × 3.4 cm2 on various paper substrates, large-scale MSC arrays (comprising up to 100 cells) can be printed to deliver a working voltage window of 160 V at an ultrahigh scan rate up to 30 V s-1. The ultrahigh rate capability enables the MSC arrays to quickly capture and efficiently store the high-voltage (≈150 V) pulse electricity produced by a droplet-based electricity generator at a high efficiency of 62%, significantly higher than that (<2%) of the batteries or capacitors demonstrated in the literature. Moreover, the compact and metal-free features make these MSC arrays excellent candidates for sustainable high-performance energy storage in self-charging power systems.

Direct Ink Writing of Low-Concentration MXene/Aramid Nanofiber Inks for Tunable Electromagnetic Shielding and Infrared Anticounterfeiting Applications

MXene inks offer a promising avenue for the scalable production and customization of printing electronics. However, simultaneously achieving a low solid content and printability of MXene inks, as well as mechanical flexibility and environmental stability of printed objects, remains a challenge. In this study, we overcame these challenges by employing high-viscosity aramid nanofibers (ANFs) to optimize the rheology of low-concentration MXene inks. The abundant entangled networks and hydrogen bonds formed between MXene and ANF significantly increase the viscosity and yield stress up to 103 Pa·s and 200 Pa, respectively. This optimization allows the use of MXene/ANF (MA) inks at low concentrations in direct ink writing and other high-viscosity processing techniques. The printable MXene/ANF inks with a high conductivity of 883.5 S/cm were used to print shields with customized structures, achieving a tunable electromagnetic interference shielding effectiveness (EMI SE) in the 0.2-48.2 dB range. Furthermore, the MA inks exhibited adjustable infrared (IR) emissivity by changing the ANF ratio combined with printing design, demonstrating the application for infrared anticounterfeiting. Notably, the printed MXene/ANF objects possess outstanding mechanical flexibility and environmental stability, which are attributed to the reinforcement and protection of ANF. Therefore, these findings have significant practical implications as versatile MXene/ANF inks can be used for customizable, scalable, and cost-effective production of flexible printed electronics.

The status and challenging perspectives of 3D-printed micro-batteries

In the era of the Internet of Things and wearable electronics, 3D-printed micro-batteries with miniaturization, aesthetic diversity and high aspect ratio, have emerged as a recent innovation that solves the problems of limited design diversity, poor flexibility and low mass loading of materials associated with traditional power sources restricted by the slurry-casting method. Thus, a comprehensive understanding of the rational design of 3D-printed materials, inks, methods, configurations and systems is critical to optimize the electrochemical performance of customizable 3D-printed micro-batteries. In this review, we offer a key overview and systematic discussion on 3D-printed micro-batteries, emphasizing the close relationship between printable materials and printing technology, as well as the reasonable design of inks. Initially, we compare the distinct characteristics of various printing technologies, and subsequently emphatically expound the printable components of micro-batteries and general approaches to prepare printable inks. After that, we focus on the outstanding role played by 3D printing design in the device architecture, battery configuration, performance improvement, and system integration. Finally, the future challenges and perspectives concerning high-performance 3D-printed micro-batteries are adequately highlighted and discussed. This comprehensive discussion aims at providing a blueprint for the design and construction of next-generation 3D-printed micro-batteries.

Large-Scale Production and Integrated Application of Micro-Supercapacitors

Micro-supercapacitors, emerging as promising micro-energy storage devices, have attracted significant attention due to their unique features. This comprehensive review focuses on two key aspects: the scalable fabrication of MSCs and their diverse applications. The review begins by elucidating the energy storage mechanisms and guiding principles for designing high-performance devices. It subsequently explores recent advancements in scalable fabrication techniques for electrode materials and micro-nano fabrication technologies for micro-devices. The discussion encompasses critical application domains, including multifunctional MSCs, energy storage integration, integrated power generation, and integrated applications. Despite notable progress, there are still some challenges such as large-scale production of electrode material, well-controlled fabrication technology, and scalable integrated manufacture. The summary concludes by emphasizing the need for future research to enhance micro-supercapacitor performance, reduce production costs, achieve large-scale production, and explore synergies with other energy storage technologies. This collective effort aims to propel MSCs from laboratory innovation to market viability, providing robust energy storage solutions for MEMS and portable electronics.

Nanocellulose based ultra-elastic and durable foams for smart packaging applications

Foams with advanced sensing properties and excellent mechanical properties are promising candidates for smart packaging materials. However, the fabrication of ultra-elastic and durable foams is still challenging. Herein, we report a universal strategy to obtain ultra-elastic and durable foams by crosslinking cellulose nanofiber and MXene via strong covalent bonds and assembling the composites into anisotropic cellular structures. The obtained composite foam shows an excellent compressive strain of up to 90 % with height retention of 97.1 % and retains around 90.3 % of its original height even after 100,000 compressive cycles at 80 % strain. Their cushioning properties were systematically investigated, which are superior to that of wildly-used petroleum-based expanded polyethylene and expanded polystyrene. By employing the foam in a piezoelectric sensor, a smart cushioning packaging and pressure monitoring system is constructed to protect inner precision cargo and detect endured pressure during transportation for the first time.

Recent progress in electrode materials for micro-supercapacitors

Micro-supercapacitors (MSCs) stand out in the field of micro energy storage devices due to their high power density, long cycle life, and environmental friendliness. The key to improving the electrochemical performance of MSCs is the selection of appropriate electrode materials. To date, both the composition and structure of electrode materials in MSCs have become a hot research topic, and it is urgent to compose a review to highlight the most important research achievements, major challenges, opportunities, and encouraging perspectives in this field. In this review, research background of MSCs is first reviewed followed by their working principles, structural classifications, and physiochemical and electrochemical characterization techniques. Next, various materials and preparation methods are summarized, and the relationship between the MSC performance and structure and composition of materials are discussed in depth. Finally, this review provides a comprehensive suggestion on accelerating the development of electrode materials to facilitate the commercialization of MSCs.

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.

Stretchable Zn‐Ion Hybrid Capacitor with Hydrogel Encapsulated 3D Interdigital Structure

To enhance the areal energy density of current flexible energy storage devices, hybrid capacitors combining the advantages of supercapacitors and batteries are proposed and further enhanced by incorporating the 3D interdigital structure design. However, uneven electric field distribution and hindered ion diffusion kinetics due to the non‐electroactive components in these devices limit the enhancement of areal electrochemical performances when expanding the electrodes longitudinally. Herein, hydrogels with high ionic conductivity and high mechanical stability are designed to accommodate Zn2+‐containing electrolytes and integrated with Ti3C2Tx‐MXene electrodes to assemble flexible Zn‐ion hybrid capacitors (ZIHCs). Fully encapsulated by ionic conductive hydrogels, 3D interdigital electrodes enable omnidirectional ion transport and unimpeded ionic accessibility, facilitating adequate electrode reactions, rapid energy storage, and uniform energy distribution. Hence, the all‐hydrogel‐encapsulated ZIHC achieved a 50‐fold increase in capacitance with a quadrupled electrode thickness, exhibiting a large areal capacitance of 1432 mF cm−2 and an energy density of 389.7 µWh cm−2 without sacrificing power density and rate performance. Finite element simulations further illustrate the uniform distribution of potential, electric field intensity, and energy density in this structure. In addition, the device shows great stability under deformation, excellent adhesion, and underwater workability, demonstrating great promise for next‐generation wearable energy storage devices.

Nanoparticle Assembly: From Self-Organization to Controlled Micropatterning for Enhanced Functionalities

Nanoparticles form long-range micropatterns via self-assembly or directed self-assembly with superior mechanical, electrical, optical, magnetic, chemical, and other functional properties for broad applications, such as structural supports, thermal exchangers, optoelectronics, microelectronics, and robotics. The precisely defined particle assembly at the nanoscale with simultaneously scalable patterning at the microscale is indispensable for enabling functionality and improving the performance of devices. This article provides a comprehensive review of nanoparticle assembly formed primarily via the balance of forces at the nanoscale (e.g., van der Waals, colloidal, capillary, convection, and chemical forces) and nanoparticle-template interactions (e.g., physical confinement, chemical functionalization, additive layer-upon-layer). The review commences with a general overview of nanoparticle self-assembly, with the state-of-the-art literature review and motivation. It subsequently reviews the recent progress in nanoparticle assembly without the presence of surface templates. Manufacturing techniques for surface template fabrication and their influence on nanoparticle assembly efficiency and effectiveness are then explored. The primary focus is the spatial organization and orientational preference of nanoparticles on non-templated and pre-templated surfaces in a controlled manner. Moreover, the article discusses broad applications of micropatterned surfaces, encompassing various fields. Finally, the review concludes with a summary of manufacturing methods, their limitations, and future trends in nanoparticle assembly.

The Need for Smart Materials in an Expanding Smart World: MXene-Based Wearable Electronics and Their Advantageous Applications

As a result of the transformation of inflexible electronic structures into flexible and stretchy devices, wearable electronics now provide great advantages in a variety of fields, including mobile healthcare sensing and monitoring, human-machine interfaces, portable energy storage and harvesting, and more. Because of their enriched surface functionalities, large surface area, and high electrical conductivity, transition metal nitrides and carbides (also known as MXenes) have recently come to be extensively considered as a group of functioning two-dimensional nanomaterials as well as exceptional fundamental elements for forming flexible electronics devices. This Review discusses the most recent advancements that have been made in the field of MXene-enabled flexible electronics for wearable electronics. The emphasis is placed on extensively established nonstructural features in order to highlight some MXene-enabled electrical devices that were constructed on a nanometric scale. These attributes include devices configured in three dimensions: printed materials, bioinspired structures, and textile and planar substrates. In addition, sample applications in electromagnetic interference (EMI) shielding, energy, healthcare, and humanoid control of machinery illustrate the exceptional development of these nanodevices. The increasing potential of MXene nanoparticles as a new area in next-generation wearable electronic technologies is projected in this Review. The design challenges associated with these electronic devices are also discussed, and possible solutions are presented.

Recent Advances and Strategies in MXene-Based Electrodes for Supercapacitors: Applications, Challenges and Future Prospects

With the growing demand for technologies to sustain high energy consumption, supercapacitors are gaining prominence as efficient energy storage solutions beyond conventional batteries. MXene-based electrodes have gained recognition as a promising material for supercapacitor applications because of their superior electrical conductivity, extensive surface area, and chemical stability. This review provides a comprehensive analysis of the recent progress and strategies in the development of MXene-based electrodes for supercapacitors. It covers various synthesis methods, characterization techniques, and performance parameters of these electrodes. The review also highlights the current challenges and limitations, including scalability and stability issues, and suggests potential solutions. The future outlooks and directions for further research in this field are also discussed, including the creation of new synthesis methods and the exploration of novel applications. The aim of the review is to offer a current and up-to-date understanding of the state-of-the-art in MXene-based electrodes for supercapacitors and to stimulate further research in the field.

Separator Engineering Based on Cl-Terminated MXene Ink: Enhancing Li+ Diffusion Kinetics with a Highly Stable Double-Halide Solid Electrolyte Interphase

Separator engineering is a promising route to designing advanced lithium (Li) metal anodes for high-performance Li metal batteries (LMBs). Conventional separators are incapable of regulating the Li+ diffusion across the solid electrolyte interphase (SEI), leading to severe dendritic deposition. To address this issue, a polypropylene (PP) separator modified by spray coating the Cl-terminated titanium carbonitride MXene ink is designed (PP@Ti3CNCl2). The lithiophilic MXene provides excellent electrolyte wettability and low Li+ diffusion barriers, finally enhancing the Li+ diffusion kinetics of excessively stable SEI. The X-ray photoelectron spectroscopy depth profiling as well as cryo-transmission electron microscopy reveals that a gradient SEI hierarchy with evenly distributed LiF and LiCl is spontaneously formed during the electrochemical process. As a consequence, PP@Ti3CNCl2 delivers a high Coulombic efficiency (99.15%) coupled with a prolonged lifespan of over 5500 h in half cells and 3100 cycles at 2 C in full cells. This work offers an effective strategy for constructing dendrite-free and Li+ permeable interfaces toward high-energy-density LMBs.

Laser-Induced MXene-Functionalized Graphene Nanoarchitectonics-Based Microsupercapacitor for Health Monitoring Application

Microsupercapacitors (micro-SCs) with mechanical flexibility have the potential to complement or even replace microbatteries in the portable electronics sector, particularly for portable biomonitoring devices. The real-time biomonitoring of the human body's physical status using lightweight, flexible, and wearable micro-SCs is important to consider, but the main limitation is, however, the low energy density of micro-SCs as compared to microbatteries. Here using a temporally and spatially controlled picosecond pulsed laser, we developed high-energy-density micro-SCs integrated with a force sensing device to monitor a human body's radial artery pulses. The photochemically synthesized spherical laser-induced MXene (Ti3C2Tx)-derived oxide nanoparticles uniformly attached to laser-induced graphene (LIG) act as active electrode materials for micro-SCs. The molecular dynamics simulations and detailed spectroscopic analysis reveal the synergistic interfacial interaction mechanism of Ti-O-C covalent bonding between MXene and LIG. The incorporation of MXene nanosheets improves the graphene sheet alignment and ion transport while minimizing self-restacking. Furthermore, the micro-SCs based on a nano-MXene-LIG hybrid demonstrate high mechanical flexibility, durability, ultrahigh energy density (21.16 × 10-3 mWh cm-2), and excellent capacitance (∼100 mF cm-2 @ 10 mV s-1) with long cycle life (91% retention after 10 000 cycles). Such a single-step roll-to-roll highly reproducible manufacturing technique using a picosecond pulsed laser to induce MXene-derived spherical oxide nanoparticles (size of quantum dots) attached uniformly to laser-induced graphene for biomedical device fabrication is expected to find a wide range of applications.

Screen-Printing Technology for Scale Manufacturing of Perovskite Solar Cells

As a key contender in the field of photovoltaics, third-generation thin-film perovskite solar cells (PSCs) have gained significant research and investment interest due to their superior power conversion efficiency (PCE) and great potential for large-scale production. For commercialization consideration, low-cost and scalable fabrication is of primary importance for PSCs, and the development of the applicable film-forming techniques that meet the above requirements plays a key role. Currently, large-area perovskite films are mainly produced by printing techniques, such as slot-die coating, inkjet printing, blade coating, and screen-printing. Among these techniques, screen printing offers a high degree of functional layer compatibility, pattern design flexibility, and large-scale ability, showing great promise. In this work, the advanced progress on applying screen-printing technology in fabricating PSCs from technique fundamentals to practical applications is presented. The fundamentals of screen-printing technique are introduced and the state-of-the-art studies on screen-printing different functional layers in PSCs and the control strategies to realize fully screen-printed PSCs are summarized. Moreover, the current challenges and opportunities faced by screen-printed perovskite devices are discussed. This work highlights the critical significance of high throughput screen-printing technology in accelerating the commercialization course of PSCs products.

Printed Electrodes Based on Vanadium Dioxide and Gold Nanoparticles for Asymmetric Supercapacitors

Printed energy storage components attracted attention for being incorporated into bendable electronics. In this research, a homogeneous and stable ink based on vanadium dioxide (VO2) is hydrothermally synthesized with a non-toxic solvent. The structural and morphological properties of the synthesized material are determined to be well-crystalline monoclinic-phase nanoparticles. The charge storage mechanisms and evaluations are specified for VO2 electrodes, gold (Au) electrodes, and VO2/Au electrodes using cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. The VO2 electrode shows an electrical double layer and a redox reaction in the positive and negative voltage ranges with a slightly higher areal capacitance of 9 mF cm-2. The VO2/Au electrode exhibits an areal capacitance of 16 mF cm-2, which is double that of the VO2 electrode. Due to the excellent electrical conductivity of gold, the areal capacitance 18 mF cm-2 of the Au electrode is the highest among them. Based on that, Au positive electrodes and VO2 negative electrodes are used to build an asymmetric supercapacitor. The device delivers an areal energy density of 0.45 μWh cm-2 at an areal power density of 70 μW cm-2 at 1.4 V in the aqueous electrolyte of potassium hydroxide. We provide a promising electrode candidate for cost-effective, lightweight, environmentally friendly printed supercapacitors.

3D-printed epifluidic electronic skin for machine learning-powered multimodal health surveillance

The amalgamation of wearable technologies with physiochemical sensing capabilities promises to create powerful interpretive and predictive platforms for real-time health surveillance. However, the construction of such multimodal devices is difficult to be implemented wholly by traditional manufacturing techniques for at-home personalized applications. Here, we present a universal semisolid extrusion-based three-dimensional printing technology to fabricate an epifluidic elastic electronic skin (e3-skin) with high-performance multimodal physiochemical sensing capabilities. We demonstrate that the e3-skin can serve as a sustainable surveillance platform to capture the real-time physiological state of individuals during regular daily activities. We also show that by coupling the information collected from the e3-skin with machine learning, we were able to predict an individual's degree of behavior impairments (i.e., reaction time and inhibitory control) after alcohol consumption. The e3-skin paves the path for future autonomous manufacturing of customizable wearable systems that will enable widespread utility for regular health monitoring and clinical applications.

Can MXene be the Effective Nanomaterial Family for the Membrane and Adsorption Technologies to Reach a Sustainable Green World?

Environmental pollution has intensified and accelerated due to a steady increase in the number of industries, and exploring methods to remove hazardous contaminants, which can be typically divided into inorganic and organic compounds, have become inevitable. Therefore, the development of efficacious technology for the separation processes is of paramount importance to ensure the environmental remediation. Membrane and adsorption technologies garnered attention, especially with the use of novel and high performing nanomaterials, which provide a target-specific solution. Specifically, widespread use of MXene nanomaterials in membrane and adsorption technologies has emerged due to their intriguing characteristics, combined with outstanding separation performance. In this review, we demonstrated the intrinsic properties of the MXene family for several separation applications, namely, gas separation, solvent dehydration, dye removal, separation of oil-in-water emulsions, heavy metal ion removal, removal of radionuclides, desalination, and other prominent separation applications. We highlighted the recent advancements used to tune separation potential of the MXene family such as the manipulation of surface chemistry, delamination or intercalation methods, and fabrication of composite or nanocomposite materials. Moreover, we focused on the aspects of stability, fouling, regenerability, and swelling, which deserve special attention when the MXene family is implemented in membrane and adsorption-based separation applications.

Micro-Cup Architecture for Printing and Coating Asymmetric 2d-Material-Based Solid-State Supercapacitors

High energy density micro-supercapacitors (MSCs) are in high demand for miniaturized electronics and microsystems. Research efforts today focus on materials development, applied in the planar interdigitated, symmetric electrode architecture. A novel "cup & core" device architecture that allows for printing of asymmetric devices without the need of accurately positioning the second finger electrode here have been introduced. The bottom electrode is either produced by laser ablation of a blade-coated graphene layer or directly screen-printed with graphene inks to create grids with high aspect ratio walls forming an array of "micro-cups". A quasi-solid-state ionic liquid electrolyte is spray-deposited on the walls; the top electrode material -MXene inks- is then spray-coated to fill the cup structure. The architecture combines the advantages of interdigitated electrodes for facilitated ion-diffusion, which is critical for 2D-material-based energy storage systems by providing vertical interfaces with the layer-by-layer processing of the sandwich geometry. Compared to flat reference devices, volumetric capacitance of printed "micro-cups" MSC increased considerably, while the time constant decreased (by 58%). Importantly, the high energy density (3.99 µWh cm-2 ) of the "micro-cups" MSC is also superior to other reported MXene and graphene-based MSCs.

Ti3 C2 TX MXene Ink Direct Writing Flexible Sensors for Disposable Paper Toys

Flexible electronics have gained great attention in recent years owing to their promising applications in biomedicine, sustainable energy, human-machine interaction, and toys for children. Paper mainly produced from cellulose fibers is attractive substrate for flexible electronics because it is biodegradable, foldable, tailorable, and light-weight. Inspired by daily handwriting, the rapid prototyping of sensing devices with arbitrary patterns can be achieved by directly drawing conductive inks on flat or curved paper surfaces; this provides huge freedom for children to design and integrate "do-it-yourself (DIY)" electronic toys. Herein, viscous and additive-free ink made from Ti3 C2 TX MXene sediment is employed to prepare disposable paper electronics through a simple ball pen drawing. The as-drawn paper sensors possess hierarchical microstructures with interweaving nanosheets, nanoflakes, and nanoparticles, therefore exhibiting superior mechanosensing performances to those based on single/fewer-layer MXene nanosheets. As proof-of-concept applications, several popular children's games are implemented by the MXene-based paper sensors, including "You say, I guess," "Emotional expression," "Rock-Paper-Scissors," "Arm wrestling," "Throwing game," "Carrot squat," and "Grab the cup," as well as a DIY smart whisker for a cartoon mouse. Moreover, MXene-based paper sensors are safe and disposable, free from producing any e-waste and hazard to the environment.

Stable MXene Dough with Ultrahigh Solid Fraction and Excellent Redispersibility toward Efficient Solution Processing and Industrialization

Two-dimensional (2D) transition metal carbides, and/or nitrides, so-called MXenes, have triggered intensive research interests in applications ranging from electrochemical energy storage to electronics devices. Producing these functional devices by printing necessitates to match the rheological properties of MXene dispersions to the requirements of various solution processing techniques. In particular, for additive manufacturing such as extrusion-printing, MXene inks with high solid fraction are typically required, which is commonly achieved by tediously removing excessive free water (top-down route). Here, the study reports on a bottom-up route to reach a highly concentrated binary MXene-water blend, so-called MXene dough, by controlling the water admixture to freeze-dried MXene flakes by exposure to water mist. The existence of a critical threshold of MXene solid content (≈60%), beyond which no dough is formed, or formed with compromised ductility is revealed. Such metallic MXene dough possesses high electrical conductivity, excellent oxidation stability, and can withstand a couple of months without apparent decay, providing that the MXene dough is properly stored at low-temperature with suppressed dehydration environment. Solution processing of the MXene dough into a micro-supercapacitor with gravimetric capacitance of 161.7 F g-1 is demonstrated. The impressive chemical and physical stability/redispersibility of MXene dough indicate its great promise in future commercialization.

MXene Contact Engineering for Printed Electronics

MXenes emerging as an amazing class of 2D layered materials, have drawn great attention in the past decade. Recent progress suggest that MXene-based materials have been widely explored as conductive electrodes for printed electronics, including electronic and optoelectronic devices, sensors, and energy storage systems. Here, the critical factors impacting device performance are comprehensively interpreted from the viewpoint of contact engineering, thereby giving a deep understanding of surface microstructures, contact defects, and energy level matching as well as their interaction principles. This review also summarizes the existing challenges of MXene inks and the related printing techniques, aiming at inspiring researchers to develop novel large-area and high-resolution printing integration methods. Moreover, to effectually tune the states of contact interface and meet the urgent demands of printed electronics, the significance of MXene contact engineering in reducing defects, matching energy levels, and regulating performance is highlighted. Finally, the printed electronics constructed by the collaborative combination of the printing process and contact engineering are discussed.

A Review of Epidermal Flexible Pressure Sensing Arrays

In recent years, flexible pressure sensing arrays applied in medical monitoring, human-machine interaction, and the Internet of Things have received a lot of attention for their excellent performance. Epidermal sensing arrays can enable the sensing of physiological information, pressure, and other information such as haptics, providing new avenues for the development of wearable devices. This paper reviews the recent research progress on epidermal flexible pressure sensing arrays. Firstly, the fantastic performance materials currently used to prepare flexible pressure sensing arrays are outlined in terms of substrate layer, electrode layer, and sensitive layer. In addition, the general fabrication processes of the materials are summarized, including three-dimensional (3D) printing, screen printing, and laser engraving. Subsequently, the electrode layer structures and sensitive layer microstructures used to further improve the performance design of sensing arrays are discussed based on the limitations of the materials. Furthermore, we present recent advances in the application of fantastic-performance epidermal flexible pressure sensing arrays and their integration with back-end circuits. Finally, the potential challenges and development prospects of flexible pressure sensing arrays are discussed in a comprehensive manner.

Recent progress in energy, environment, and electronic applications of MXene nanomaterials

Since the discovery of graphene, two-dimensional (2D) materials have gained widespread attention, owing to their appealing properties for various technological applications. Etched from their parent MAX phases, MXene is a newly emerged 2D material that was first reported in 2011. Since then, a lot of theoretical and experimental work has been done on more than 30 MXene structures for various applications. Given this, in the present review, we have tried to cover the multidisciplinary aspects of MXene including its structures, synthesis methods, and electronic, mechanical, optoelectronic, and magnetic properties. From an application point of view, we explore MXene-based supercapacitors, gas sensors, strain sensors, biosensors, electromagnetic interference shielding, microwave absorption, memristors, and artificial synaptic devices. Also, the impact of MXene-based materials on the characteristics of respective applications is systematically explored. This review provides the current status of MXene nanomaterials for various applications and possible future developments in this field.

Molecular precursor mediated selective synthesis of phase pure cubic InSe and hexagonal In2Se3 nanostructures: new anode materials for Li-ion batteries

Indium selenides (InSe and In₂Se₃) have earned a special place among the 2D layered metal chalcogenides owing to their nontoxic nature and favourable carrier mobility. Additionally, they are also being projected as next generation battery anodes with high theoretical lithium-ion storage capacities. While the development of indium selenide-based batteries is still in its embryonic stage, a simple and easily scalable synthetic pathway to access these materials is highly desirable for energy storage applications. This study reports a controlled synthetic route to nanometric cubic InSe and hexagonal In₂Se₃ materials through proper choice of coordinating solvents from a structurally characterized air and moisture stable single source molecular precursor: tris(4,6-dimethyl-2-pyrimidylselenolato)indium(III). The crystal structure, phase purity, composition, morphology and band gap of the nanomaterials were thoroughly evaluated by pXRD, energy dispersive X-ray spectroscopy (EDS), electron microscopy (SEM and TEM), and diffuse reflectance spectroscopy (DRS), respectively. The pristine InSe and In₂Se₃ nanostructures have been employed as anode materials in lithium-ion batteries (LIBs). Both the cells deliver reasonably high initial discharge capacities with a cyclability of 200 and 620 cycles for cubic InSe and hexagonal In₂Se₃ respectively with ∼100% coulombic efficiency.

Ultrastretchable MXene Microsupercapacitors

Stretchable microsupercapacitors represent emerging miniaturized energy-storage devices for next-generation deformable electronics. Two-dimensional (2D) transition metal carbides (MXenes) are considered attractive electrode materials due to their metallic conductivity, hydrophilic surfaces, and excellent processability. Here, an ultrastretchable microsupercapacitor of interdigitated MXene microelectrodes with crumpled surface textures is created. The microsupercapacitor shows a series of attractive properties including a high specific capacitance of ≈185 mF cm^-2 , ultrahigh stretchability up to 800% area strain, and ≈89.7% retention of the initial capacitance after 1000 stretch-relaxation cycles. In addition to static strains, the microsupercapacitor demonstrates robust mechanical properties to retain stable charging-discharging capability under dynamic stretching at different strain rates. A self-powering circuit system utilizes four microsupercapacitor packs to power a light-emitting diode (LED) array, which exhibits stable operations under large tensile strain and skin-attached wearable settings. The developments offer a generic design strategy to enhance the deformability of microsupercapacitors based on 2D nanomaterials.

A Single Electronic Tattoo for Multisensory Integration

Wearable electronics are garnering growing interest in various emerging fields including intelligent sensors, artificial limbs, and human-machine interfaces. A remaining challenge is to develop multisensory devices that can conformally adhere to the skin even during dynamic-moving environments. Here, a single electronic tattoo (E-tattoo) based on a mixed-dimensional matrix network, which integrates two-dimensional  MXene nanosheets and one-dimensional cellulose nanofibers/Ag nanowires, is presented for multisensory integration. The multidimensional configurations endow the E-tattoo with excellent multifunctional sensing capabilities including temperature, humidity, in-plane strain, proximity, and material identification. In addition, benefiting from the satisfactory rheology of hybrid inks, the E-tattoos are able to be fabricated through multiple facile strategies including direct writing, stamping, screen printing, and three-dimensional printing on various hard/soft substrates. Especially, the E-tattoo with excellent triboelectric properties also can serve as a power source for activating small electronic devices. It is believed that these skin-conformal E-tattoo systems can provide a promising platform for next-generation wearable and epidermal electronics.

Recent advances in inkjet-printing technologies for flexible/wearable electronics

The rapid development of flexible/wearable electronics requires novel fabricating strategies. Among the state-of-the-art techniques, inkjet printing has aroused considerable interest due to the possibility of large-scale fabricating flexible electronic devices with good reliability, high time efficiency, a low manufacturing cost, and so on. In this review, based on the working principle, recent advances in the inkjet printing technology in the field of flexible/wearable electronics are summarized, including flexible supercapacitors, transistors, sensors, thermoelectric generators, wearable fabric, and for radio frequency identification. In addition, some current challenges and future opportunities in this area are also addressed. We hope this review article can give positive suggestions to the researchers in the area of flexible electronics.

Recent advances in the synthesis and electrocatalytic application of MXene materials

MXenes are a class of two-dimensional materials with a graphene-like structure, which have excellent optical, biological, thermodynamic, electrical and magnetic properties. Due to the diversity resulting from the combination of transition metals and C/N, the MXene family has expanded to more than 30 members and been applied in many fields with broad application prospects. Among their applications, electrocatalytic applications have achieved many breakthroughs. Therefore, in this review, we summarize the reports on the preparation of MXenes and their application in electrocatalysis published in the last five years and describe the two main methods for the preparation of MXenes, i.e., bottom-up and top to bottom synthesis. Different methods may change the structure or surface termination of MXenes, and accordingly affect their electrocatalytic performance. Furthermore, we highlight the application of MXenes in the electrocatalytic hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), carbon dioxide reduction reaction (CO₂RR), nitrogen reduction reaction (NRR), and multi-functionalization. It can be concluded that the electrocatalytic properties of MXenes can be modified by changing the type of functional groups or doping. Also, MXenes can be compounded with other materials to produce electronic coupling and improve the catalytic activity and stability of the resulting composites. In addition, Mo₂C and Ti₃C₂ are two types of MXene materials that have been widely studied in the field of electrocatalysis. At present, research on the synthesis of MXenes is focused on carbides, whereas research on nitrides is rare, and there are no synthesis methods meeting the requirements of green, safety, high efficiency and industrialization simultaneously. Therefore, it is very important to explore environmentally friendly industrial production routes and devote more research efforts to the synthesis of MXene nitrides.

Recent advances in polyaniline-based micro-supercapacitors

The rapid development of the Internet of Things (IoTs) and proliferation of wearable electronics have significantly stimulated the pursuit of distributed power supply systems that are small and light. Accordingly, micro-supercapacitors (MSCs) have recently attracted tremendous research interest due to their high power density, good energy density, long cycling life, and rapid charge/discharge rate delivered in a limited volume and area. As an emerging class of electrochemical energy storage devices, MSCs using polyaniline (PANI) electrodes are envisaged to bridge the gap between carbonaceous MSCs and micro-batteries, leading to a high power density together with improved energy density. However, despite the intensive development of PANI-based MSCs in the past few decades, a comprehensive review focusing on the chemical properties and synthesis of PANI, working mechanisms, design principles, and electrochemical performances of MSCs is lacking. Thus, herein, we summarize the recent advances in PANI-based MSCs using a wide range of electrode materials. Firstly, the fundamentals of MSCs are outlined including their working principle, device design, fabrication technology, and performance metrics. Then, the working principle and synthesis methods of PANI are discussed. Afterward, MSCs based on various PANI materials including pure PANI, PANI hydrogel, and PANI composites are discussed in detail. Lastly, concluding remarks and perspectives on their future development are presented. This review can present new ideas and give rise to new opportunities for the design of high-performance miniaturized PANI-based MSCs that underpin the sustainable prosperity of the approaching IoTs era.

Improving the Performance of Paper-Based Dipole Antennas by Electromagnetic Flux Concentration

One of the essential issues in modern advanced materials science is to design and manufacture flexible devices, in particular in the framework of the Internet of Things (IoT), to improve integration into applications. An antenna is an essential component of wireless communication modules and, in addition to flexibility, compact dimensions, printability, low cost, and environmentally friendlier production strategies, also represent relevant functional challenges. Concerning the antenna's performance, the optimization of the reflection coefficient and maximum range remain the key goals. In this context, this work reports on screen-printed paper@Ag-based antennas and optimizes their functional properties, with improvements in the reflection coefficient (S₁₁) from -8 to -56 dB and maximum transmission range from 208 to 256 m, with the introduction of a PVA-Fe₃O₄@Ag magnetoactive layer into the antenna's structure. The incorporated magnetic nanostructures allow the optimization of the functional features of antennas with possible applications ranging from broadband arrays to portable wireless devices. In parallel, the use of printing technologies and sustainable materials represents a step toward more sustainable electronics.