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We propose and demonstrate a flexible surface-enhanced Raman scattering (SERS) chip as a versatile platform for femtomolar detection and real-time interfacial molecule analysis. The flexible SERS chip is composed of a flexible and transparent membrane and embedded plasmonic dimers with ultrahigh particle density and ultrasmall dimer gap. The chip enables rapid identification for residuals on solid substrates with irregular surfaces or dissolved analytes in aqueous solution. The sensitivity for liquid-state measurement is down to 0.06 molecule per dimers for 10-14 mol·L-1 Rhodamine 6G molecule without molecule enrichment. Strong signal fluctuation and blinking are observed at this concentration, indicating that the detection limit is close to the single-molecule level. Meanwhile, the homogeneous liquid environment facilities accurate SERS quantification of analytes with a wide dynamic range. The synergy of flexibility and liquid-state measurement opens up avenues for the real-time study of chemical reactions. The reduction from p-nitrothiophenol (PNTP) to p-aminothiophenol (PATP) in the absence of the chemical reducing agents is observed at liquid interfaces by in situ SERS measurements, and the plasmon-induced hot electron is demonstrated to drive the catalytic reaction. We believe this robust and feasible approach is promising in extending the SERS technique as a general method for identifying interfacial molecular traces, tracking the evolution of heterogeneous reactions, elucidating the reaction mechanisms, and evaluating the environmental effects such as pH value and salty ions in SERS.

The rapid development of miniaturized electronic systems stimulates the demand for microscale power sources. Microscale rechargeable batteries (μRBs) are one promising candidate for the microscale energy storage due to high energy density, long cycling stability, and excellent compatibility with electronic devices. The progress in microscale rechargeable batteries from two-dimensional to three-dimensional configurations are first summarized. The advantage of three-dimensional configurations is extensively discussed. The growing demand for high-energy-density microdevices requires significant improvement of current μRBs, thus making it urgent to obtain an in-depth understanding of electrochemical behaviors in microbatteries. In this perspective, the in-situ/in-operando analytical platforms for efficient investigation of microelectrodes are comprehensively reviewed. Moreover, the design principle of the on-site investigation of microscale batteries is highlighted. Finally, we discuss essential challenges in both device configuration and materials optimization strategies.

The great development of lightweight and portable smart electronic devices has significantly stimulated the interests in exploring and developing miniaturized energy storage systems. High-performance micro-supercapacitors (MSCs) with three-dimensional (3D) nanostructures show a great potential to improve energy storage capability, and these types of MSCs are regarded as ideal stand-alone power sources for smart microelectronics. Here, Cu0.56Co2.44O4@MnO2 core–shell nanoflowers and carbon nanotubes are integrated into a 3D hybrid asymmetric MSC with a fast, convenient, and scalable production fashion. Due to the hierarchical structure of the 3D electrodes and active materials, the hybrid MSC exhibits an improved specific areal capacitance of 665.3 ​mF ​cm−2 at 3.2 ​mA ​cm−2 and an excellent cycling performance of 89.8% retention after 8000 cycles. The MSC also shows an ultrahigh energy density of 182.3 ​μW ​h ​cm−2, which is higher than almost all the previously reported energy density values of on-chip interdigital-electrode MSCs. The efficient fabrication methodology of both the materials and the device demonstrated in this work show great potential in developing high-performance 3D MSCs.

Improve materials and architectures to shrink microscopic devices. Improve materials and architectures to shrink microscopic devices.

An efficient catalyst with a precisely designed and predictable structure is highly desired to optimize its performance and understand the mechanism beyond the catalytic activity. Covalent organic frameworks (COFs), as an emerging class of framework materials linked by strong covalent bonds, simultaneously allow precise structure design with predictable synthesis and show advantages of large surface areas, tunable pore sizes, and unique molecular architectures. Although the research on COF���based electrocatalysts is at an early age, significant progress has been made. Herein, the recent significant progress in the design and synthesis of COFs as highly efficient electrocatalysts for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) is summarized. Design principles for COFs as efficient electrocatalysts are discussed by considering essential factors for catalyzing the OER, ORR, and HER processes at the molecular level. Herein, a summary on the in���depth understanding of the catalytic mechanism and kinetics limitations of COFs provides a general instruction for further exploring their vast potential for designing highly efficient electrocatalysts.

In article number 2001561, Ming Huang, Feng Zhu, Oliver G. Schmidt, and co‐workers develop a costeffective stamping strategy for scalable and rapid preparation of graphene‐based flexible micro‐supercapacitors. The efficient production of the flexible micro‐supercapacitor devices with outstanding shape diversity, high areal capacitance and excellent cycling stability shows great potential for future applications in portable and wearable electronics. [Image: see text]

Supercapacitors have received considerable attention owing to high power density, high safety and great cycling performance. Great efforts have been devoted to hunting new materials for supercapacitor applications. In this work, we report a novel nanomaterial of LaB 6 nanowires (NWs) on carbon fiber cloth serving as active electrochemical materials for supercapacitors. The LaB 6-carbon fiber cloth electrodes could work in two different electrolytes including 1 M Na2SO4 and 1M H2SO4. The as-prepared LaB6 NWs electrode delivered a significant areal capacitance as high as 17.34 mF cm−2 in 1.0 M Na2SO4 solution at a current density of 0.1 mA cm−2. Moreover, the LaB6 NWs electrode displayed outstanding cycling stability after 10,000 charging/discharging cycles. The electrochemical charge/discharge mechanism in 1M Na2SO4 was studied. This work lay the foundations for developing LaB6 NWs as supercapacitor electrode and open the door to the design of boride nanomaterials for energy storage applications.

High-performance energy storage devices are in urgent need due to the fast development of wearable electronics, while the challenge of achieving outstanding flexibility has not been properly addressed yet, let alone the safety, another critical issue determines their practicability. Herein, we report a quasi-solid-state aqueous rechargeable lithium-ion battery (ARLIB) based on carbon cloth substrates and PVA-LiNO3 gel polymer electrolyte (GPE). Thanks to the protective PPy coating layer on LiV3O8 and the use of solid GPE, the as-assembled ARLIB exhibits a good cycling stability of 98.7% and 79.8% capacity retention after 100 and 500 cycles, respectively. It also demonstrates exceptional flexibility to sustain various deformations including bending, squeezing, twisting and folding because of its solid-state design. Moreover, the ARLIB can be tailored into any desired shapes, and even be punched penetrative holes, exhibiting excellent safety. Thus, the creation of numerous tiny through-holes across the whole ARLIB body is testified feasible, and a designed breathability catering to the demand of comfortability in wearable devices is subsequently realized. Obviously, our study offers a promising strategy to construct flexible energy storage device with outstanding stability, flexibility, safety and breathability towards various wearable electronics.

Exploration of a highly efficient and multifunctional electrocatalytic material is crucial for renewable energy technologies. Herein, by studying a multidimensional and multifunctional Co/N–C catalyst, we have demonstrated that two categories of preferential characteristics, i.e. activity distinctions between different reactions and feature distinctions between component and structure aspects, for electrocatalysts are not mutually exclusive, but can be well-addressed simultaneously. This rationally designed and cost-effective hybrid catalyst synergically integrates the features, including ample active species, prompt mass transport, excellent conductivity, and structural stability in both acidic and alkaline electrolytes, for an efficient and versatile electrocatalyst. The thus-obtained multidimensional catalyst delivers excellent activities in oxygen reduction and overall water-splitting reactions in conjunction with a good durability, which then enables a prominent performance in a rechargeable Zn–air battery and also demonstrates feasibility in a self-powered water-splitting unit. This study opens up new avenues for the rational design and easy fabrication of multidimensional catalysts with desired performances for various renewable energy applications.

Beyond the traditional focus on improvements in mechanical, electronic and absorption properties, controllability, actuation, and dynamic response of monoliths have received increasing attentions for practical applications. However, most of them could only realize simple response to constant conditions (e.g. a stationary magnetic field) while carrying out humdrum motions. By controlling distribution of metal organic framework obtained carbon-enriched Fe3O4 nanoparticles in self-assembly reduced graphene oxide (RGO) monoliths, we could achieve two distinctive RGO–Fe3O4 stirrers that could dynamically respond to the rapidly changing magnetic field while executing designed movements precisely: rotating with lying down posture or standing straight posture. These stirrers can not only be applied in environmental remediation (e.g. suction skimmer), but also be recycled as electrode active materials for supercapacitors after fulfilling their destiny, realizing transformation of trash to treasure, which will inspire other dynamically responsive monoliths for various applications.

Flexible and safe batteries, coupled with high performance and low cost, constitute a radical advance in portable and wearable electronics, especially considering the fact that these flexible devices are likely to experience more mechanical impacts and potential damage than well-protected rigid batteries. However, flexible lithium ion batteries (LIBs) are vastly limited by their intrinsic safety and cost issues. Here we introduce an extremely safe and wearable solid-state zinc ion battery (ZIB) comprising a novel gelatin and PAM based hierarchical polymer electrolyte (HPE) and an α-MnO2 nanorod/carbon nanotube (CNT) cathode. Benefiting from the well-designed electrolyte and electrodes, the flexible solid-state ZIB delivers a high areal energy density and power density (6.18 mW h cm−2 and 148.2 mW cm−2, respectively), high specific capacity (306 mA h g−1) and excellent cycling stability (97% capacity retention after 1000 cycles at 2772 mA g−1). More importantly, the solid-state ZIB offers a high wearability and an extreme safety performance over conventional flexible LIBs, and performs very well under various severe conditions, such as being greatly cut, bent, hammered, punctured, sewed, washed in water or even put on fire. In addition, flexible ZIBs were integrated in series to power a commercial smart watch, a wearable pulse sensor, and a smart insole, which has been achieved to the best of our knowledge for the first time. These results demonstrate the promising potential of ZIBs in many practical wearable applications and offer a new platform for flexible and wearable energy storage technologies.

Fiber-shaped supercapacitors have attracted widely attention for their great potential application in future portable and wearable electronics compared with traditional 2D planar structured supercapacitors, which is associated to their high flexibility, tiny volume and good deformability. Asymmetric designed supercapacitors usually couple two different electrodes with a Faradaic or battery-type electrode as the energy source role and a non-faradaic (or electric double-layer) electrode as the power source in one configuration, and thus can operate in much wider potential windows than that of the symmetrical design, thus potentially leading to a substantial increase in the energy density. Here, we focused on the recent progresses and advances of fiber-shaped asymmetric supercapacitors (FASCs) with respect to their electrode materials, design and configuration. Firstly, capacitive and pseudocapacitive materials, such as carbon materials, conductive polymers and metal oxides/sulfides/nitrides, are comprehensively discussed with the scope of their working potential ranges, proper electrolytes and working principles. Then the progresses to date on the FASCs including the device design, electrode fabrication and electrochemical performance of the FASCs are summarized. Finally, a short conclusion is made, combining with the future perspectives in this rapid developing area.

Facile yet rational design of an efficient reversible oxygen electrocatalyst is critical for many renewable energy conversion and storage technologies. Here we report a simple and general synthetic protocol for fabricating a hierarchically porous and heteroatom doped carbon catalyst, which exhibited outstanding oxygen reduction/evolution activities (with a metric potential difference of 0.72 V in 1 M KOH, the best value for metal-free catalysts reported to date) with good stability in different electrolytes. The excellent performances of the catalyst were primarily endowed by our synthetic protocol, which integrates good conductivity, abundant accessible dopant species and suitable porous architectures within an in situ pyrolysis reaction. As a result, the performances of rechargeable Zn–air batteries based on the optimized catalyst substantially outperform those afforded by a benchmark Pt/C catalyzer. Our work is expected to open up new avenues for developing other efficient catalysts in a facile and viable way.

Polypyrrole (PPy), as one of the conducting polymers, has emerged as a promising active material for high performance supercapacitor owing to its intrinsic characteristics ( e.g. high electrical conductivity and interesting redox properties). It’s attracting more and more attentions with the development of flexible/wearable devices thanks to the great flexibility and ductility of PPy as a polymer. This review presents a comprehensive understanding on synthesis, morphology control, electrochemical performances and solid-state devices of the nanostructured PPy and its nanocomposites. In the past decades, a variety of nanostructures, including one-, two-, and three-dimensional, have been designed and fabricated via different methods, demonstrating a great potential for the application as supercapacitor electrodes. Thereafter, many nanostructured PPy-based supercapacitors with different macroscopic configurations have been presented aiming to achieve better electrochemical performance, and some representative ones, for example, flexible and/or wearable supercapacitors, are summarized in this review. Cycling stability is another critical issue that determines its practicability of the PPy-based devices. Solutions to improve cycling performance and mechanisms behind are also discussed. Last, perspectives for the future development in nanostructured PPy-based supercapacitors are described. This review gives a summary of selected contributions which we hope to provide readers with a better understanding of the fast developing field of PPy-based supercapacitors.

We report a general approach to achieve greatly boosted efficiency of electrochemical process in the photoelectrochemical (PEC) water splitting reaction and supercapacitive process by simultaneously enhancing charge transfer and creating active sites in TiO2 nanotube arrays (TNAs) electrodes. Shallow donor defects self-doping and MnOx deposition are adopted to fulfill the two desired roles, respectively. Our results clearly demonstrated that the enhanced charge transfer resulted from vacuum induced defect self-doping could dramatically improve the water splitting performance and areal capacitance of the pristine TNAs, whilst the deposited manganese oxide species, serving as electrochemically active sites, can further substantially boost their energy conversion and storage efficiencies. As a result, the MnOx/TNAs anode exhibited a photoconversion efficiency of 0.56% in neutral Na2SO4, which is the highest value of TiO2 anode in the same electrolyte under AM 1.5 G illumination. Also, the composite electrode presented an areal capacitance of 12.51 mF cm−2 at 5 mV s−1, nearly three orders of magnitude lager than that of the pristine TNAs counter electrode. Moreover, a specific capacitance of 1117 F g−1 (at 5 mV s−1) was achieved based on the mass of deposited MnO2, which also ranks in the top performance level of MnO2 based supercapacitor devices. It is hoped that the present work may shed new light on achieving enhanced performance in energy conversion and storage devices.

Linear-shaped supercapacitors are promising candidates for powering portable as well as wearable electronics, because of their small volume, high flexibility and outstanding electrochemical performance. It is even more desirable to embed additional functionalities into these supercapacitors, and consequently exploiting their application area. We thus introduced a novel modularization approach for linear functional supercapacitors, aiming at realizing rapid assembling. This approach is largely based on the common module, a self-standing polypyrrole (PPy)-based tube, obtained by using a reciprocal formwork construction technique. With the assistance of an elastic solid electrolyte and flexible graphene, the integrity of the inner PPy film in this common module could be perfectly retained even after detachment, which ensured outstanding performance of the resultant functional devices. By combining this common module with other building blocks, three kinds of high performance prototypes could be easily achieved, including cable-shaped shape memory supercapacitors, cable-shaped supercapacitor yarns and asymmetric cable-shaped supercapacitors, meeting the requirements of different applications. Our modularization approach creatively applied a common module in different functional supercapacitor systems reducing the workload significantly, meanwhile inspiring other brilliant modular designs for various coaxial linear devices.

Fiber-shaped supercapacitors, which are energy-storage devices that feature flexibility and wearability, could realize further gains in energy-storage performance if their electrodes are properly designed. Herein, we present a high energy-performance and flexible fiber-shaped supercapacitor by using PEDOT@MnO2 and C@Fe3O4 composites as the positive and negative electrodes, respectively. The as-fabricated fiber-shaped supercapacitor with a high working voltage of 2 V exhibits a high areal specific capacitance of 60 mF cm−2 and a large energy density of 0.0335 mW h cm−2. This fiber-shaped supercapacitor exhibits good flexibility and particularly can be deformed without energy-performance decay. Furthermore, this fiber-shaped supercapacitor woven into a wristband in series can successfully power a LED, indicating its promising practical application in wearable electronics.

As a result of the popularization of wearable electronics, a variety of compact flexible energy storage devices have been successfully developed recently. During practical application, these delicate devices unavoidably experience all kinds of deformations. These deformations would become irreversible under the long-term concentration of local stresses, leading to structure and functional fatigue. To solve this problem, a shape memory supercapacitor (SMSC) is successfully fabricated for the first time. The SMSC is flexible and easily deformed below its activation temperature. Once it is heated over a trigger temperature, it would automatically recover its original shape, meanwhile restoring all deformations. By embedding with shape memory functions, all potential damage to the supercapacitor would be nipped in the bud, while simultaneously prolonging the life span of the device. Furthermore, an energy storage shape memory textile woven with these SMSCs and traditional fabrics can work as a smart sleeve. It can “remember” its pre-designed shape and realize automatic cooling when it is over-heated, demonstrating a diversity of potential applications other than energy storage.

Fluorescent monolayer boron nitride based quantum dots, including boron nitride quantum dots and boron carbon oxynitride quantum dots, were successfully fabricated via a hydrothermal method by cutting the bulk material assisted by a basic solution. The boron nitride/boron carbon oxynitride quantum dots are water-soluble with uniform lateral sizes around 3.3 and 4.0 nm respectively. The application of the as-prepared quantum dots as promising bio-imaging probes was demonstrated through labeling HeLa cells with boron nitride/boron carbon oxynitride quantum dots, indicating single layered boron nitride/boron carbon oxynitride quantum dots could be further used in biological applications.

Flexible energy storage devices have attracted wide attention because of the increasing requirement of wearable electronics. However, comfortability, productivity, and feasibility, to name a few, are still far from satisfactory in the current wearable supercapacitors (SCs). This is largely due to the missing of an ideal low-cost flexible substrate/current collector that should not only exhibit high conductivity, but also be compatible with modern textile technologies. Herein, we apply the traditional gilding technique to cloth and successfully convert the cloth to be an excellent current collector which is available at a reasonable cost and compatible with textile technologies. Thanks to the strong electrostatic interaction, we found that a positively charged gold leaf could be laminated on a negatively charged polyester cloth intimately. This substrate could perfectly act as an integrated compact electrode after the electrodeposition of polypyrrole nanorods. The resulting electrode is mechanically strong enough to withstand the tortures of repeated bending, cutting, or puncturing, and is readily assembled into wearable SCs and energy cloth with outstanding practicability, for example, safety and breathability. It is foreseeable that our work will inspire a series design of wearable electronics based on the fascinating gilding art.

Yarn-based supercapacitors have received considerable attention recently, offering unprecedented opportunities for future wearable electronic devices (e.g., smart clothes). However, the reliability and lifespan of yarn-based supercapacitors can be seriously limited by accidental mechanical damage during practical applications. Therefore, a supercapacitor endowed with mechanically and electrically self-healing properties is a brilliant solution to the challenge. Compared with the conventional planar-like or large wire-like structure, the reconnection of the broken yarn electrode composed of multiple tiny fibers (diameter20 μm) is much more difficult and challenging, which directly affects the restoration of electrical conductivity after damage. Herein, a self-healable yarn-based supercapacitor that ensures the reconnection of broken electrodes has been successfully developed by wrapping magnetic electrodes around a self-healing polymer shell. The strong force from magnetic attraction between the broken yarn electrodes benefits reconnection of fibers in the yarn electrodes during self-healing and thus offers an effective strategy for the restoration of electric conductivity, whereas the polymer shell recovers the configuration integrity and mechanical strength. With the design, the specific capacitance of our prototype can be restored up to 71.8% even after four breaking/healing cycles with great maintenance of the whole device's mechanical properties. This work may inspire the design and fabrication of other distinctive self-healable and wearable electronic devices.

The performance and cycling stability of stretchable energy storage devices, such as supercapacitors and batteries, are limited by the structural breakdown arising from the stretch imposed and large volumetric swelling/shrinking. This work demonstrates a very facile and low-cost approach to fabricate stretchable supercapacitors with high performance and excellent cycling stability by electrochemical deposition of polypyrrole (PPy) on smartly-tailored stretchable stainless steel meshes. The fabricated solid-state supercapacitors possess a capacitance up to 170 F/g at a specific current of 0.5 A/g and it can be effectively enhanced to 214 F/g with a 20% strain. Moreover, they can be operated at a very high scan rate up to 10 V/s, which are 1–2 orders of magnitude higher than most rates for the PPy electrodes measured even in aqueous electrolytes. Even significantly, the fabricated solid-state supercapacitors under 0% and 20% strains achieve remarkable capacitance retentions of 98% and 87% at a very high specific current of 10 A/g after 10,000 cycles, respectively, which are the best for PPy-based solid-state flexible supercapacitors, to the best of our knowledge. The key factors and mechanisms to achieve such high performance are discussed. This facile and low-cost approach developed for fabricating stable and stretchable supercapacitors with high performances could pave the way for next-generation stretchable electronics.

Inspired by cooking omelettes, a facile, low-cost and scalable method involving the use of a readily available household non-stick frying pan is introduced to fabricate large-area freestanding reduced graphene oxide (RGO) paper. The as-fabricated RGO paper is robust enough to bear sandpaper polishing, bending/folding, and hydrothermal and electrochemical deposition processes without obvious structure/performance degradation. As a demonstration, the as-obtained RGO papers were directly used as universal flexible substrates for high performance supercapacitors (SCs). Thus, WO3 and PPy, which are two distinctive active materials, were loaded onto the RGO paper via a hydrothermal process and electrodeposition process, respectively, which are two typical fabrication methods for high performance SC electrodes. The resultant WO3– and PPy–RGO paper, which act as negative and positive electrodes, respectively, were further assembled into a flexible asymmetric supercapacitor (ASC), achieving a high energy density of 0.23 mW h cm−3 at a power density of 7.3 mW cm−3 when normalized to the whole volume. Moreover, benefiting from the robust flexible RGO substrate, the performance of the ASC showed great stability under different bending angles and after repeated bending/folding. These exciting results demonstrate that our robust RGO paper is an ideal universal substrate for different active materials synthesized via various processing methods, which show its great potential in an all-solid energy storage system with excellent flexibility and robustness.

A highly durable high-performance all-polymer micro-supercapacitor with plug-and-play function is developed. Through the newly developed technology, these micro-supercapacitors can be transferred to any substrate with all functions well retained.

Polypyrrole (PPy), as one of the conducting polymers, has emerged as a promising active material for high performance supercapacitor owing to its intrinsic characteristics ( e.g. high electrical conductivity and interesting redox properties). It’s attracting more and more attentions with the development of flexible/wearable devices thanks to the great flexibility and ductility of PPy as a polymer. This review presents a comprehensive understanding on synthesis, morphology control, electrochemical performances and solid-state devices of the nanostructured PPy and its nanocomposites. In the past decades, a variety of nanostructures, including one-, two-, and three-dimensional, have been designed and fabricated via different methods, demonstrating a great potential for the application as supercapacitor electrodes. Thereafter, many nanostructured PPy-based supercapacitors with different macroscopic configurations have been presented aiming to achieve better electrochemical performance, and some representative ones, for example, flexible and/or wearable supercapacitors, are summarized in this review. Cycling stability is another critical issue that determines its practicability of the PPy-based devices. Solutions to improve cycling performance and mechanisms behind are also discussed. Last, perspectives for the future development in nanostructured PPy-based supercapacitors are described. This review gives a summary of selected contributions which we hope to provide readers with a better understanding of the fast developing field of PPy-based supercapacitors.

Multifunctional energy storage and conversion devices that incorporate novel features and functions in intelligent and interactive modes, represent a radical advance in consumer products, such as wearable electronics, healthcare devices, artificial intelligence, electric vehicles, smart household, and space satellites, etc. Here, smart energy devices are defined to be energy devices that are responsive to changes in configurational integrity, voltage, mechanical deformation, light, and temperature, called self-healability, electrochromism, shape memory, photodetection, and thermal responsivity. Advisable materials, device designs, and performances are crucial for the development of energy electronics endowed with these smart functions. Integrating these smart functions in energy storage and conversion devices gives rise to great challenges from the viewpoint of both understanding the fundamental mechanisms and practical implementation. Current state-of-art examples of these smart multifunctional energy devices, pertinent to materials, fabrication strategies, and performances, are highlighted. In addition, current challenges and potential solutions from materials synthesis to device performances are discussed. Finally, some important directions in this fast developing field are considered to further expand their application.

The cycling stability of flexible supercapacitors with conducting polymers as electrodes is limited by the structural breakdown arising from repetitive counterion flow during charging/discharging. Supercapacitors made of facilely electropolymerized polypyrrole (e-PPy) have ultrahigh capacitance retentions of more than 97, 91, and 86% after 15000, 50000, and 100000 charging/discharging cycles, respectively, and can sustain more than 230000 charging/discharging cycles with still approximately half of the initial capacitance retained. To the best of our knowledge, such excellent long-term cycling stability was never reported. The fully controllable electropolymerization shows superiority in molecular ordering, favoring uniform stress distribution and charge transfer. Being left at ambient conditions for even 8 months, e-PPy supercapacitors completely retain the good electrochemical performance. The extremely stable supercapacitors with excellent flexibility and scalability hold considerable promise for the commerical application of flexible and wearable electronics.

Nanomaterials with layered structures, with their intriguing properties, are of great research interest nowadays. As one of the primary two-dimensional nanomaterials, the hexagonal boron nitride nanosheet (BNNS, also called white graphene), which is an analogue of graphene, possesses various attractive properties, such as high intrinsic thermal conductivity, excellent chemical and thermal stability, and electrical insulation properties. After being discovered, it has been one of the most intensively studied two-dimensional non-carbon nanomaterials and has been applied in a wide range of applications. To support the exploration of applications of BNNSs, exfoliation, as one of the most promising approaches to realize large-scale production of BNNSs, has been intensively investigated. In this review, methods to yield BNNSs by exfoliation will be summarized and compared with other potential fabrication methods of BNNSs. In addition, the future prospects of the exfoliation of h-BN will also be discussed.

A field-effect transistor (FET) based on ultrathin Ti3 C2 -MXene micropatterns is developed and utilized as a highly sensitive biosensor. The device is produced with the microcontact printing technique, making use of its unique advantages for easy fabrication. Using the MXene-FET device, label-free probing of small molecules in typical biological environments and fast detection of action potentials in primary neurons is demonstrated.

Superior self-healability and stretchability are critical elements for the practical wide-scale adoption of personalized electronics such as portable and wearable energy storage devices. However, the low healing efficiency of self-healable supercapacitors and the small strain of stretchable supercapacitors are fundamentally limited by conventional polyvinyl alcohol-based acidic electrolytes, which are intrinsically neither self-healable nor highly stretchable. Here we report an electrolyte comprising polyacrylic acid dual crosslinked by hydrogen bonding and vinyl hybrid silica nanoparticles, which displays all superior functions and provides a solution to the intrinsic self-healability and high stretchability problems of a supercapacitor. Supercapacitors with this electrolyte are non-autonomic self-healable, retaining the capacitance completely even after 20 cycles of breaking/healing. These supercapacitors are stretched up to 600% strain with enhanced performance using a designed facile electrode fabrication procedure., Materials for wearable energy storage devices should be mechanically durable. Here, the authors report a supercapacitor composed of polyacrylic acid dual cross-linked by hydrogen bonding and vinyl hybrid silica nanoparticles which is self-healable and retains performance when stretched up to 600%.

Wearable electronic textiles that store capacitive energy are a next frontier in personalized electronics. However, the lack of industrially weavable and knittable conductive yarns in conjunction with high capacitance, limits the wide-scale application of such textiles. Here pristine soft conductive yarns are continuously produced by a scalable method with the use of twist-bundle-drawing technique, and are mechanically robust enough to be knitted to a cloth by a commercial cloth knitting machine. Subsequently, the reduced-graphene-oxide-modified conductive yarns covered with a hierarchical structure of MnO2 nanosheets and a polypyrrole thin film were used to fabricate weavable, knittable and wearable yarn supercapacitors. The resultant modified yarns exhibit specific capacitances as high as 36.6 mF cm(-1) and 486 mF cm(-2) in aqueous electrolyte (three-electrode cell) or 31 mF cm(-1) and 411 mF cm(-2) in all solid-state two-electrode cell. The symmetric solid-state supercapacitor has high energy densities of 0.0092 mWh cm(-2) and 1.1 mWh cm(-3) (both normalized to the whole device) with a long cycle life. Large energy storage textiles are fabricated by weaving our flexible all-solid-state supercapacitor yarns to a 15 cm × 10 cm cloth on a loom and knitting in a woollen wrist band to form a pattern, enabling dual functionalities of energy storage capability and wearability.

Intrinsic short hole diffusion length is a well-known problem for α-Fe2O3 as a visible-light photocatalytic material. In this paper, a nanodisk morphology was designed to remarkably enhance separation of electron-hole pairs of α-Fe2O3. As expected, α-Fe2O3 nanodisks presented superior photocatalytic activity toward methylene blue degradation: more than 90% of the dye could be photodegraded within 30 min in comparison with a degradation efficiency of 50% for conventional Fe2O3 powder. The unique multilayer structure is thought to play a key role in the remarkably improved photocatalytic performance. Further experiments involving mechanism investigations revealed that instead of high surface area, ·OH plays a crucial role in methylene blue degradation and that O·2- may also contribute effectively to the degradation process. This paper demonstrates a facile and energy-saving route to fabricating homogenous α-Fe2O3 nanodisks with superior photocatalytic activity that is suitable for the treatment of contaminated water and that meets the requirement of mass production.

The performance of many stretchable electronics, such as energy storage devices and strain sensors, is highly limited by the structural breakdown arising from the stretch imposed. In this article, we focus on a detailed study on materials matching between functional materials and their conductive substrate, as well as enhancement of the tolerance to stretch-induced performance degradation of stretchable supercapacitors, which are essential for the design of a stretchable device. It is revealed that, being widely utilized as the electrode material of the stretchable supercapacitor, metal oxides such as MnO2 nanosheets have serious strain-induced performance degradation due to their rigid structure. In comparison, with conducting polymers like a polypyrrole (PPy) film as the electrochemically active material, the performance of stretchable supercapacitors can be well preserved under strain. Therefore, a smart design is to combine PPy with MnO2 nanosheets to achieve enhanced tolerance to strain-induced performance degradation of MnO2-based supercapacitors, which is realized by fabricating an electrode of PPy-penetrated MnO2 nanosheets. The composite electrodes exhibit a remarkable enhanced tolerance to strain-induced performance degradation with well-preserved performance over 93% under strain. The detailed morphology and electrochemical impedance variations are investigated for the mechanism analyses. Our work presents a systematic investigation on the selection and matching of electrode materials for stretchable supercapacitors to achieve high performance and great tolerance to strain, which may guide the selection of functional materials and their substrate materials for the next-generation of stretchable electronics.

Recently, wearable electronic devices including electrical sensors, flexible displays, and health monitors have received considerable attention and experienced rapid progress. Wearable supercapacitors attract tremendous attention mainly due to their high stability, low cost, fast charging/discharging, and high efficiency; properties that render them value for developing fully flexible devices. In this Concept, the recent achievements and advances made in flexible and wearable supercapacitors are presented, especially highlighting the promising performances of yarn/fiber-shaped and planar supercapacitors. On the basis of their working mechanism, electrode materials including carbon-based materials, metal oxide-based materials, and conductive polymers with an emphasis on the performance-optimization method are introduced. The latest representative techniques and active materials of recently developed supercapacitors with superior performance are summarized. Furthermore, the designs of 1D and 2D electrodes are discussed according to their electrically conductive supporting materials. Finally, conclusions, challenges, and perspective in optimizing and developing the electrochemical performance and function of wearable supercapacitors for their practical utility are addressed.

The fabrication of photoluminescent Ti3 C2 MXene quantum dots (MQDs) by a facile hydrothermal method is reported, which may greatly extend the applications of MXene-based materials. Interestingly, the as-prepared MQDs show excitation-dependent photoluminescence spectra with quantum yields of up to ≈10% due to strong quantum confinement. The applications of MQDs as biocompatible multicolor cellular imaging probes and zinc ion sensors are demonstrated.

Though polypyrrole (PPy) is widely used in flexible supercapacitors owing to its high electrochemical activity and intrinsic flexibility, limited capacitance and cycling stability of freestanding PPy films greatly reduce their practicality in real-world applications. Herein, we report a new approach to enhance PPy's capacitance and cycling stability by forming a freestanding and conductive hybrid film through intercalating PPy into layered Ti3C2 (l-Ti3C2, a MXene material). The capacitance increases from 150 (300) to 203 mF cm−2 (406 F cm−3). Moreover, almost 100% capacitance retention is achieved, even after 20 000 charging/discharging cycles. The analyses reveal that l-Ti3C2 effectively prevents dense PPy stacking, benefiting the electrolyte infiltration. Furthermore, strong bonds, formed between the PPy backbones and surfaces of l-Ti3C2, not only ensure good conductivity and provide precise pathways for charge-carrier transport but also improve the structural stability of PPy backbones. The freestanding PPy/l-Ti3C2 film is further used to fabricate an ultra-thin all-solid-state supercapacitor, which shows an excellent capacitance (35 mF cm−2), stable performance at any bending state and during 10 000 charging/discharging cycles. This novel strategy provides a new way to design conductive polymer-based freestanding flexible electrodes with greatly improved electrochemical performances.