The 50 most-cited articles in Advanced Functional Materials, 2019

Abstract In this review, the factors influencing the power conversion efficiency (PCE) of perovskite solar cells (PSCs) is emphasized. The PCE of PSCs has remarkably increased from 3.8% to 23.7%, but on the other hand, poor stability is one of the main facets that creates a huge barrier in the commercialization of PSCs. Herein, a concise overview of the current efforts to enhance the stability of PSCs is provided; moreover, the degradation causes and mechanisms are summarized. The strategies to improve device stability are portrayed in terms of structural effects, a photoactive layer, hole‐ and electron‐transporting layers, electrode materials, and device encapsulation. Last but not least, the economic feasibility of PSCs is also vividly discussed.

Abstract Adhering hydrogels to various materials is fundamental to a large array of established and emerging applications. The last few years have seen transformative advances in achieving strong hydrogel adhesion, which is a supramolecular phenomenon. Two adherends connect through covalent bonds, noncovalent complexes, polymer chains, polymer networks, or nanoparticles. Separating the adherends dissipates energy through cascading events across length scales, including bond cleavage, chain retraction, and bulk hysteresis. A unifying principle has emerged: strong hydrogel adhesion requires the synergy of chemistry of bonds, topology of connection, and mechanics of dissipation. This synergy characterizes hydrogel adhesion to various materials (another hydrogel, tissue, elastomer, plastic, metal, glass, and ceramic) in various operations (cast, coat, print, attach, pierce, and glue). Strong adhesion can be made permanent, reversible, degradable, or on‐demand detachable. The development of hydrogel adhesion and its applications adheres disciplines, discovers interlinks, and forges…

Abstract In recent years, nanomedicine has emerged at the forefront of nanotechnology, generating great expectations in the biomedical field. Researchers are developing novel nanoparticles for both diagnostic applications using imaging technology and treatment purposes through drug delivery technologies. Among all the available nanoparticles, inorganic mesoporous silica nanoparticles are the newcomers to the field, contributing with their unique and superlative properties. A brief overview of the most recent progress in the synthesis of mesoporous silica nanoparticles and their use as drug delivery nanocarriers is provided. The latest trends in this type of nanoparticles and their use in modern medicine are discussed, highlighting the significant impact that this technology might have in the near future.

Abstract Low‐dimensional materials have been long sought after for their particular electromagnetic (EM) functions, with promising applications in EM wave absorbing and shielding, communicating and imaging, sensing and detecting, driving and actuating, etc. Herein, across the whole EM spectrum, low‐dimensional EM functional materials and devices are highly focused on. The crystal engineering and function‐guiding features addressed relate to crystal and electronic structures, EM responses and properties, energy conversion, as well as EM wave absorbing and shielding. Moreover, insight is given into this rapidly broadening field, the main challenges are proposed and future directions are predicted.

Abstract Conductive hydrogels are attracting tremendous interest in the field of flexible and wearable soft strain sensors because of their great potential in electronic skins, and personalized healthcare monitoring. However, conventional conductive hydrogels using pure water as the dispersion medium will inevitably freeze at subzero temperatures, resulting in the diminishment of their conductivity and mechanical properties; meanwhile, even at room temperature, such hydrogels suffer from the inevitable loss of water due to evaporation, which leads to a poor shelf‐life. Herein, an antifreezing, self‐healing, and conductive MXene nanocomposite organohydrogel (MNOH) is developed by immersing MXene nanocomposite hydrogel (MNH) in ethylene glycol (EG) solution to replace a portion of the water molecules. The MNH is prepared from the incorporation of the conductive MXene nanosheet networks into hydrogel polymer networks. The as‐prepared MNOH exhibits an outstanding antifreezing property (−40 °C), long‐lasting moisture retention (8 d), excellent self‐healing capability, and superior…

Abstract The microwave absorption (MA) performance of carbon materials is severely hindered by their drawbacks of lacking magnetic loss ability and mismatched electromagnetic impedance. In this work, utilizing sustainable biomass kapok as a template, the hierarchically tubular C/Co nanoparticle composite is rationally constructed to acquire the enhanced MA performance for the first time. The fruit‐tree‐like hierarchical structure is composed from a “trunk” of kapok‐derived carbon microtubes, a “branch” of entangled carbon nanotubes, and “fruit” of Co nanoparticles embedded in the nanotubes. Such a hierarchically tubular structure offers the composite: i) a submillimeter‐scale 3D magnetic coupling network and reinforced magnetic loss ability, ii) a hierarchical dielectric carbon network, iii) better matched impedance, confirmed by the off‐axis electron holography and micromagnetic simulation. Accordingly, the as‐prepared hierarchically tubular carbon composite demonstrates impressive MA performance, with a maximum reflection loss of as much as −52.3 dB and a broad absorption…

Abstract The manganese dissolution leading to sharp capacity decline as well as the sluggish reaction kinetic are still major issues for manganese‐based materials as aqueous zinc‐ion batteries (ZIBs) cathodes. Here, a potassium‐ion‐stabilized and oxygen‐defect K0.8Mn8O16 is reported as a high‐energy‐density and durable cathode for neutral aqueous ZIBs. A new insight into suppressing manganese dissolution via incorporation of K+ ions to intrinsically stabilize the Mn‐based cathodes is provided. A comprehensive study suggests that oxygen defects improve electrical conductivity and open the MnO6 polyhedron walls for ion diffusion, which plays a critical role in the fast reaction kinetics and capacity improvement of K0.8Mn8O16. In addition, direct evidence for the mechanistic details of simultaneous insertion and conversion reaction based on H+‐storage mechanism is demonstrated. As expected, a significant energy output of 398 W h kg−1 (based on the mass of cathode) and an impressive durability over 1000 cycles with no obvious capacity fading are obtained. Such a high‐energy…

Abstract Although flexible and multifunctional textiles are promising for wearable electronics and portable device applications, the main issue is to endow textiles with multifunctionalities while maintaining their innate flexible and porous features. Herein, a vacuum‐assisted layer‐by‐layer assembly technique is demonstrated to conformally deposit electrically conductive substances on textiles for developing multifunctional and flexible textiles with superb electromagnetic interference (EMI) shielding performances, superhydrophobicity, and highly sensitive humidity response. The formed leaf‐like nanostructure is composed of silver nanowires (AgNWs) as the highly conductive skeleton (vein) and transition metal carbide/carbonitride (MXene) nanosheets as the lamina. The presence of MXene protects AgNWs from oxidation and enhances the combination of AgNWs with the fabric substrate, and the transformation of its functional groups leads to self‐derived hydrophobicity. The flexible and multifunctional textile exhibits a low sheet resistance of 0.8 Ω sq−1, outstanding EMI shielding…

Abstract Simulating biological synapses with electronic devices is a re‐emerging field of research. It is widely recognized as the first step in hardware building brain‐like computers and artificial intelligent systems. Thus far, different types of electronic devices have been proposed to mimic synaptic functions. Among them, transistor‐based artificial synapses have the advantages of good stability, relatively controllable testing parameters, clear operation mechanism, and can be constructed from a variety of materials. In addition, they can perform concurrent learning, in which synaptic weight update can be performed without interrupting the signal transmission process. Synergistic control of one device can also be implemented in a transistor‐based artificial synapse, which opens up the possibility of developing robust neuron networks with significantly fewer neural elements. These unique features of transistor‐based artificial synapses make them more suitable for emulating synaptic functions than other types of devices. However, the development of transistor‐based artificial…

Abstract Dielectric energy‐storage capacitors have received increasing attention in recent years due to the advantages of high voltage, high power density, and fast charge/discharge rates. Here, a new environment‐friendly 0.76NaNbO 3 –0.24(Bi 0.5 Na 0.5 )TiO 3 relaxor antiferroelectric (AFE) bulk ceramic is studied, where local orthorhombic Pnma symmetry (R phase) and nanodomains are observed based on high‐resolution transmission electron microscopy, selected area electron diffraction, and in/ex situ synchrotron X‐ray diffraction. The orthorhombic AFE R phase and relaxor characteristics synergistically contribute to the record‐high energy‐storage density W rec of ≈12.2 J cm −3 and acceptable energy efficiency η ≈ 69% at 68 kV mm −1 , showing great advantages over currently reported bulk dielectric ceramics. In comparison with normal AFEs, the existence of large random fields in the relaxor AFE matrix and intrinsically high breakdown strength of NaNbO 3 ‐based compositions are thought to be responsible for the observed energy‐storage performances. Together with the good thermal…

Abstract Due to its significant applications in many relevant fields, light detection in the solar‐blind deep‐ultraviolet (DUV) wavelength region is a subject of great interest for both scientific and industrial communities. The rapid advances in preparing high‐quality ultrawide‐bandgap (UWBG) semiconductors have enabled the realization of various high‐performance DUV photodetectors (DUVPDs) with different geometries, which provide an avenue for circumventing numerous disadvantages in traditional DUV detectors. This article presents a comprehensive review of the applications of inorganic UWBG semiconductors for solar‐blind DUV light detection in the past several decades. Different kinds of DUVPDs, which are based on varied UWBG semiconductors including Ga 2 O 3 , Mg x Zn 1− x O, III‐nitride compounds (Al x Ga 1− x N/AlN and BN), diamond, etc., and operate on different working principles, are introduced and discussed systematically. Some emerging techniques to optimize device performance are addressed as well. Finally, the existing techniques are summarized and future challenges are…

Abstract Dielectric materials are greatly desired for electromagnetic absorption applications. Lots of research shows that conduction loss and polarization are two of the most important factors determining complex permittivity. However, the detailed dissipation mechanisms for the improved microwave absorption performance are often based on semiempirical rules, lacking practical data relationships between conduction loss/polarization and dielectric behaviors. Here, a strategy of introducing point defects is used to understand such underlying relationships, where polarizability and conductivity are adjustable by manipulating oxygen deficiency or heteroatoms. Based on first principles calculations and the applied oxygen‐deficient strategy, dielectric polarization is shown to be dominant in determining the permittivity behaviors in semiconductors. Meanwhile, the presented nitrogen doping strategy shows that conduction loss is dominant in determining the permittivity behavior in graphitized carbon materials. The validity of the methods for using point defects to explore the underlying…

Abstract A critical challenge in the commercialization of layer‐structured Ni‐rich materials is the fast capacity drop and voltage fading due to the interfacial instability and bulk structural degradation of the cathodes during battery operation. Herein, with the guidance of theoretical calculations of migration energy difference between La and Ti from the surface to the inside of LiNi 0.8 Co 0.1 Mn 0.1 O 2 , for the first time, Ti‐doped and La 4 NiLiO 8 ‐coated LiNi 0.8 Co 0.1 Mn 0.1 O 2 cathodes are rationally designed and prepared, via a simple and convenient dual‐modification strategy of synchronous synthesis and in situ modification. Impressively, the dual modified materials show remarkably improved electrochemical performance and largely suppressed voltage fading, even under exertive operational conditions at elevated temperature and under extended cutoff voltage. Further studies reveal that the nanoscale structural degradation on material surfaces and the appearance of intergranular cracks associated with the inconsistent evolution of structural degradation at the particle…

Abstract Polymer‐based thermal interface materials (TIMs) with excellent thermal conductivity and electrical resistivity are in high demand in the electronics industry. In the past decade, thermally conductive fillers, such as boron nitride nanosheets (BNNS), were usually incorporated into the polymer‐based TIMs to improve their thermal conductivity for efficient heat management. However, the thermal performance of those composites means that they are still far from practical applications, mainly because of poor control over the 3D conductive network. In the present work, a high thermally conductive BNNS/epoxy composite is fabricated by building a nacre‐mimetic 3D conductive network within an epoxy resin matrix, realized by a unique bidirectional freezing technique. The as‐prepared composite exhibits a high thermal conductivity (6.07 W m −1 K −1 ) at 15 vol% BNNS loading, outstanding electrical resistivity, and thermal stability, making it attractive to electronic packaging applications. In addition, this research provides a promising strategy to achieve high thermal conductive…

Abstract The energy used for regulating building temperatures accounts for 14% of the primary energy consumed in the U.S. One‐quarter of this energy is leaked through inefficient glass windows in cold weather. The development of transparent composites could potentially provide affordable window materials with enhanced energy efficiency. Transparent wood as a promising material has presented desirable performances in thermal and light management. In this work, the performance of transparent wood is optimized toward an energy efficient window material that possesses the following attributes: 1) high optical transmittance (≈91%), comparable to that of glass; 2) high clarity with low haze (≈15%); 3) high toughness (3.03 MJ m−3) that is 3 orders of magnitude higher than standard glass (0.003 MJ m−3); 4) low thermal conductivity (0.19 W m−1 K−1) that is more than 5 times lower than that of glass. Additionally, the transparent wood is a sustainable material, with low carbon emissions and scaling capabilities due to its compatibility with industry‐adopted rotary cutting methods. The…

Abstract Organic light‐emitting diodes (OLEDs) have become a mainstream display technology in consumer electronics. Self‐emitting ability, transparency, true dark tone, and capability of being made flexible are some of the features of OLED displays, leading to a superior performance compared with liquid crystal displays. In addition to displays, OLEDs are also a strong candidate for lighting applications. Despite great advances in improving the internal quantum efficiency of an OLED to nearly 100%, the external quantum efficiency is still lacking behind due to optical losses. This review reports the latest advances in the optical design of OLEDs that address the external coupling efficiency of OLEDs. Discussed at first are the fundamentals of OLED optics and how the refractive indices of different layers in an OLED stack affect the extraction efficiency. Then, this paper reviews how microlens arrays, scattering layers, and corrugated structures can be used to recover the optical losses and improve the external efficiency, and the general optical designs for different optical…

Abstract Black phosphorus (BP) has increasingly attracted scientific attention since its first applications in biomedicine due to its unique properties and excellent biocompatibility. In particular, its layer‐dependent bandgap, moderate carrier mobility, large surface‐area‐to‐volume ratio, biodegradability, intrinsic photoacoustic properties, and biocompatibility make it an ideal candidate for use in photothermal therapy, photodynamic therapy, drug delivery, 3D printing, bioimaging, biosensing, and theranostics, which are reviewed here. In addition, the article discusses strategies to overcome challenges related to surface instability due to chemical degradation, a major obstacle for its application. This review not only provides a comprehensive summary on BP preparation and biomedical applications but also summarizes recent research and future possibilities.

Abstract Rechargeable aqueous zinc batteries have gained considerable attention for large‐scale energy storage systems because of their low cost and high safety, but they suffer from limitations in cycling stability and energy density with advanced cathode materials. Here, a high‐performance V5O12·6H2O (VOH) nanobelt cathode uniformly located on a stainless‐steel substrate via a facile electrodeposition technique is reported. We show that the hydrated layered VOH cathode enables highly reversible and ultrafast Zn2+ cation (de)intercalation processes, as confirmed by various electrochemical, X‐ray diffraction, X‐ray photoelectron spectroscopy, and transmission electron microscopy analyses. It is demonstrated that the binder‐free VOH cathode can deliver a discharge capacity of 354.8 mAh g−1 at 0.5 A g−1 with a high initial Coulombic efficiency of 99.5%, a high energy density of 194 Wh kg−1 at 2100 W kg−1, and a long cycle life with a capacity retention of 94% over 1000 cycles. In addition, a flexible quasi‐solid‐state Zn–VOH battery is constructed, achieving a reversible capacity of…

Abstract The rapid development of the science and technology of organic semiconductors has already led to mass application of organic light‐emitting diodes (OLEDs) in television monitors of outstanding quality as well as in a large variety of smaller displays found in smartphones, tablets, and other gadgets, while introduction of the technology to the illumination sector is imminent. Notably, the requirements of all such applications for emission in the visible range of the electromagnetic spectrum are well tuned to the optical and electronic properties of typical organic semiconductors, thereby representing relatively “low‐hanging fruits,” in terms of material development and exploitation. However, the question arises as to whether developing materials suited for efficient near‐infrared (NIR, 700–1000 nm) emission is possible, and, crucially, desirable to enable new classes of applications spanning from through‐space, short‐range communications to biomedical sensors, night vision, and more generally security applications to name but a few. Here, the major fundamental hurdles to be…

Abstract Cardiovascular disease is the leading cause of death and has dramatically increased in recent years. Continuous cardiac monitoring is particularly important for early diagnosis and prevention, and flexible and stretchable electronic devices have emerged as effective tools for this purpose. Their thin, soft, and deformable features allow intimate and long‐term integration with biotissues, which enables continuous, high‐fidelity, and sometimes large‐area cardiac monitoring on the skin and/or heart surface. In addition to monitoring, intimate contact is also crucial for high‐precision therapies. Combined with tissue engineering, soft bioelectronics have also demonstrated the capability to repair damaged cardiac tissues. This review highlights the recent advances in wearable and implantable devices based on flexible and stretchable electronics for cardiovascular monitoring and therapy. First, wearable/implantable soft bioelectronics for cardiovascular monitoring (e.g., the electrocardiogram, blood pressure, and oxygen saturation level) are reviewed. Then, advances in…

Abstract Diabetic ulcer is the most common kind of chronic wound worldwide. Though great efforts have been devoted, diabetic ulcer still remains as a challenge that requires constant monitoring and management. In this work, a multifunctional zwitterionic hydrogel is developed to simultaneously detect two fluctuant wound parameters, pH and glucose level, to monitor the diabetic wound status. A pH indicator dye (phenol red) and two glucose sensing enzymes, glucose oxidase (GOx) and horseradish peroxidase (HRP), are encapsulated in the anti‐biofouling and biocompatible zwitterionic poly‐carboxybetaine (PCB) hydrogel matrix. The visible images are collected by a smartphone and transformed into RGB signals to quantify the wound parameters. Results show that the activity and stability of both two enzymes are improved within PCB hydrogel, and the K cat / K m value of PCB‐HRP is ≈5.5 fold of free HRP in artificial wound exudate. This novel wound dressing can successfully monitor the pH range of 4–8 and glucose level of 0.1–10 × 10 −3 m . Meanwhile, it also provides a moist healing…

Abstract Exhaustive attempts are made in recent decades to improve the performance of thermoelectric materials that are utilized for waste heat‐to‐electricity conversion. Energy filtering of charge carriers is directed toward enhancing the material thermopower. This paper focuses on the theoretical concepts, experimental evidence, and the authors' view of energy filtering in the context of thermoelectric materials. Recent studies suggest that not all materials experience this effect with the same intensity. Although this effect theoretically demonstrates improvement of the thermopower, applying it poses certain constraints, which demands further research. Predicated on data documented in literature, the unusual dependence of the thermopower and conductivity upon charge carrier concentrations can be altered through the energy filtering approach. Upon surmounting the physical constraints discussed in this article, thermoelectric materials research may gain a new direction to enhance the power factor and thermoelectric figure of merit.

Abstract The ultrahigh concentration of glutathione (GSH) inside tumors destroys reactive oxygen species (ROS)‐based therapy, improving the outcome of chemodynamic therapy (CDT)‐enhanced sonodynamic therapy (SDT) by depleting GSH is full of great challenge. Herein, PtCu 3 nanocages are first reported as acting as a sonosensitizer with highly efficient ROS generation under ultrasound irradiation. In addition, PtCu 3 nanocages can act as horseradish peroxidase‐like nanozymes, catalyzing the decomposition of H 2 O 2 into • OH under acidic conditions for CDT. Surprisingly, PtCu 3 nanocages can act as another kind of nanozyme, mimicking glutathione peroxidase (GSH‐Px), which plays an important role in accelerating GSH depletion by oxidizing molecules, further weakening the capacity of tumor cells scavenging ROS by GSH. Both in vitro and in vivo studies demonstrate that PtCu 3 nanocages perform well in reducing GSH level for CDT‐enhanced SDT. Moreover, utilizing the high absorption in the near‐infrared region and strong X‐ray attenuation ability, the PtCu 3 nanocages are able to conduct…

Abstract As an important branch of wearable electronics, flexible pressure sensors have attracted extensive research owing to their wide range of applications, such as human–machine interfaces and health monitoring. To fulfill the requirements for different applications, new material design and device fabrication strategies have been developed in order to manipulate the mechanical and electrical properties and enhance device performance. In this paper, the important progresses in flexible pressure sensor development over recent years are selectively reviewed from a material and application perspective. First, an overview of the fundamental working mechanism and the systematic design approach is presented. Particularly, how the theoretical modeling has been used as an auxiliary tool to achieve better sensing performance is discussed. A number of applications, including human–machine interfaces, electronic skin and health monitoring, and certain application‐driven functions, e.g., pressure distribution visualization and direction‐sensitive force detection, are highlighted. Lastly,…

Abstract Highly efficient non‐noble metal electrocatalysts are vital for metal–air batteries and fuel cells. Herein, a noble‐metal–free single‐atom Fe‐N x‐C electrocatalyst is synthesized by incorporating Fe‐Phen complexes into the nanocages in situ during the growth of ZIF‐8, followed by pyrolysis at 900 °C under inert atmosphere. Fe‐Phen species provide both Fe2+ and the organic ligand (Phen) simultaneously, which play significant roles in preparing single‐atom catalysts. The obtained Fe‐Nx‐C exhibits a half‐wave potential of 0.91 V for the oxygen reduction reaction, higher than that of commercial Pt/C (0.82 V). As a cathode catalyst for primary zinc–air batteries (ZABs), the battery shows excellent electrochemical performances in terms of the high open‐circuit voltage (OCV) of 1.51 V and a high power density of 96.4 mW cm−2. The rechargeable ZAB with Fe‐Nx‐C catalyst and the alkaline electrolyte shows a remarkable cycling performance for 300 h with an initial round‐trip efficiency of 59.6%. Furthermore, the rechargeable all‐solid‐state ZABs with the Fe‐Nx‐C catalyst show high OCV…

Abstract Recently, artificial intelligence research has driven the development of stretchable and flexible electronic systems. Conductive hydrogels are a class of soft electronic materials that have emerging applications in wearable and implantable biomedical devices. However, current conductive hydrogels possess fundamental limitations in terms of their antibacterial performance and a mechanical mismatch with human tissues, which severely limits their applications in biological interfaces. Here, inspired by animal skin, a conductive hydrogel is fabricated from a supramolecular assembly of polydopamine decorated silver nanoparticles (PDA@Ag NPs), polyaniline, and polyvinyl alcohol, namely PDA@Ag NPs/CPHs. The resultant hydrogel has many desirable features, such as tunable mechanical and electrochemical properties, eye‐catching processability, good self‐healing ability as well as repeatable adhesiveness. Remarkably, PDA@Ag NPs/CPHs exhibit broad antibacterial activity against Gram‐negative and Gram‐positive bacteria. The potential application of this versatile hydrogel is…

Abstract Until now there has been no fundamental theory applicable for biodegradable metals (BMs). First, this paper optimizes the definition of BMs given in 2014. Second, the dual criteria of biodegradability and biocompatibility are proposed for BMs, and all metallic elements in the periodic table with accessible data are screened on the basis of these criteria. Regarding biodegradability, electrode potential, reactivity series, galvanic series, Pilling–Bedworth ratio, and Pourbaix diagrams are all adopted as parameters to classify the degradable and nondegradable nature of a material, especially in a physiological environment. Considering the biocompatibility at different levels, cellular biocompatibility, tissue biocompatibility, and human/clinical related biocompatibility parameters are put forward to comprehensively evaluate the biosafety of BMs. Third, for the material design of BMs, mechanical properties, chemical properties, physical properties and biological properties should be considered and balanced to guarantee that the degradation behavior of BMs match well with a…

Abstract Triboelectric nanogenerators (TENGs) are a promising technology to convert mechanical energy to electrical energy based on coupled triboelectrification and electrostatic induction. With the rapid development of functional materials and manufacturing techniques, wearable and implantable TENGs have evolved into playing important roles in clinic and daily life from in vitro to in vivo. These flexible and light membrane‐like devices have the potential to be a new power supply or sensor element, to meet the special requirements for portable electronics, promoting innovation in electronic devices. In this review, the recent advances in wearable and implantable TENGs as sustainable power sources or self‐powered sensors are reviewed. In addition, the remaining challenges and future possible improvements of wearable and implantable TENG‐based self‐powered systems are discussed.

Abstract Soft robots have the appealing advantages of being highly flexible and adaptive to complex environments. However, the low‐stiffness nature of the constituent materials makes soft robotic systems incompetent in tasks requiring relatively high load capacity. Despite recent attempts to develop stiffness‐tunable soft actuators by employing variable stiffness materials and structures, the reported stiffness‐tunable actuators generally suffer from limitations including slow responses, small deformations, and difficulties in fabrication with microfeatures. This work presents a paradigm to design and manufacture fast‐response, stiffness‐tunable (FRST) soft actuators via hybrid multimaterial 3D printing. The integration of a shape memory polymer layer into the fully printed actuator body enhances its stiffness by up to 120 times without sacrificing flexibility and adaptivity. The printed Joule‐heating circuit and fluidic cooling microchannel enable fast heating and cooling rates and allow the FRST actuator to complete a softening–stiffening cycle within 32 s. Numerical simulations…

Abstract Assembly of 2D MXene sheets into a 3D macroscopic architecture is highly desirable to overcome the severe restacking problem of 2D MXene sheets and develop MXene‐based functional materials. However, unlike graphene, 3D MXene macroassembly directly from the individual 2D sheets is hard to achieve for the intrinsic property of MXene. Here a new gelation method is reported to prepare a 3D structured hydrogel from 2D MXene sheets that is assisted by graphene oxide and a suitable reductant. As a supercapacitor electrode, the hydrogel delivers a superb capacitance up to 370 F g−1 at 5 A g−1, and more promisingly, demonstrates an exceptionally high rate performance with the capacitance of 165 F g−1 even at 1000 A g−1. Moreover, using controllable drying processes, MXene hydrogels are transformed into different monoliths with structures ranging from a loosely organized porous aerogel to a dense solid. As a result, a 3D porous MXene aerogel shows excellent adsorption capacity to simultaneously remove various classes of organic liquids and heavy metal ions while the dense solid has…

Abstract Semiconductor‐based photodetectors (PDs) convert light signals into electrical signals via the photoelectric effect, which involves the generation, separation, and transportation of the photoinduced charge carriers, as well as the extraction of these charge carriers to external circuits. Because of their specific electronic and optoelectronic properties, metal oxide semiconductors are widely used building blocks in photoelectric devices. However, the compromise between enhancing the photoresponse and reducing the rise/decay times limits the practical applications of PDs based on metal oxide semiconductors. As the behaviors of the charge carriers play important roles in the photoelectric conversion process of these PDs, researchers have proposed several strategies, including modification of light absorption, design of novel PD heterostructures, construction of specific geometries, and adoption of specific electrode configurations to modulate the charge‐carrier behaviors and improve the photoelectric performance of related PDs. This review aims to introduce and summarize the…

Abstract The uprising demands for electrical power and electrification requires advanced dielectric functionalities including high capacitance density, high energy density, high current handling capability, high voltage, high temperature, high thermal conductivity, light weight, and environmental reliability. Nanodielectric engineering emerges and attracts extensive efforts from many countries as a result. Unlike prior reviews focusing on lab scale nanocomposite study, this review focuses on recent innovations in polymer‐based nanodielectric design on a large scale and their film scale‐up efforts for advanced capacitors. The unconventional polymer‐nanofiller engineering and their process in the last two decades are discussed. The nanofunctionalized polymers on a molecular level for high dielectric constants and high dielectric strength are briefly described. The challenge associated with film scale‐up and retention of nanodielectric properties are then pointed out to be crucial toward a transfer of dielectric and capacitor technology. Several important attempts at scaling up…

Abstract Zinc vacancy (VZn) is successfully introduced into 3D hierarchical ZnIn2S4 (3D‐ZIS). The photo‐electrochemical experiments demonstrate that the charge separation and carrier transfer are more efficient in the 3D‐ZIS with rich VZn. Of note, for the first time, it is found that VZn can decrease the carrier transport activation energy (CTAE), from 1.14 eV for Bulk‐ZIS (Bulk ZnIn2S4) to 0.93 eV for 3D‐ZIS, which may provide a feasible platform for further understanding the mechanism of photocatalytic CO2 reduction. In situ Fourier transform infrared (FT‐IR) results reveal that the presence of rich VZn ensures CO2 chemical activation, promoting single‐electron reduction of CO2 to CO2−. In addition, in situ FT‐IR and CO2 temperature programmed desorption results show that VZn can promote the formation of surface hydroxyl. To the best of current knowledge, there are no reports on the photoreduction of CO2 simply by virtue of 3D‐ZIS with VZn and few literature reports on the photocatalytic reduction of CO2 concerned with CTAE. Additionally, this work finds that surface hydroxyl may…

Abstract Electrochemical water splitting is recognized as a practical strategy for impelling the transformation of sustainable energy sources such as solar energy from electricity to clean hydrogen fuel. To actualize the large‐scale hydrogen production, it is paramount to develop low‐cost, earth‐abundant, efficient, and stable electrocatalysts. Among those electrocatalysts, alternative architectural arrays grown on conductive substrates have been proven to be highly efficient toward water splitting due to large surface area, abundant active sites, and synergistic effects between the electrocatalysts and the substrates. Herein, the advancement of nanoarray architectures in electrocatalytic applications is reviewed. The categories of different nanoarrays and the reliable and versatile synthetic approaches of electrocatalysts are summarized. A unique emphasis is highlighted on the promising strategies to enhance the electrocatalytic activities and stability of architectural arrays by component manipulation, heterostructure regulation, and vacancy engineering. The intrinsic mechanism…

Abstract Passive radiative cooling technology can cool down an object by reflecting solar light and radiating heat simultaneously. However, photonic radiators generally require stringent and nanoscale‐precision fabrication, which greatly restricts mass production and renders them less attractive for large‐area applications. A simple, inexpensive, and scalable electrospinning method is demonstrated for fabricating a high‐performance flexible hybrid membrane radiator (FHMR) that consists of polyvinylidene fluoride/tetraethyl orthosilicate fibers with numerous nanopores inside and SiO 2 microspheres randomly distributed across its surface. Even without silver back‐coating, a 300 µm thick FHMR has an average infrared emissivity >0.96 and reflects ≈97% of solar irradiance. Moreover, it exhibits great flexibility and superior strength. The daytime cooling performance this device is experimentally demonstrated with an average radiative cooling power of 61 W m −2 and a temperature decrease up to 6 °C under a peak solar intensity of 1000 W m −2 . This performance is comparable to those of…

Abstract Organic photodetectors (OPDs) have gained increasing interest as they offer cost‐effective fabrication methods using low temperature processes, making them particularly attractive for large area image detectors on lightweight flexible plastic substrates. Moreover, their photophysical and optoelectronic properties can be tuned both at a material and device level. Visible‐light OPDs are proposed for use in indirect‐conversion X‐ray detectors, fingerprint scanners, and intelligent surfaces for gesture recognition. Near‐infrared OPDs find applications in biomedical imaging and optical communications. For most applications, minimizing the OPD dark current density ( J d ) is crucial to improve important figures of merits such as the signal‐to‐noise ratio, the linear dynamic range, and the specific detectivity ( D *). Here, a quantitative analysis of the intrinsic dark current processes shows that charge injection from the electrodes is the dominant contribution to J d in OPDs. J d reduction is typically addressed by fine‐tuning the active layer energetics and stratification or by…

Abstract Fiber supercapacitors have aroused great interest in the field of portable and wearable electronic devices. However, the restrained surface area of fibers and limited reaction kinetics of active materials are unfavorable for performance enhancement. Herein, an efficient multicomponent hierarchical structure is constructed by integrating the Cu‐doped cobalt copper carbonate hydroxide@nickel cobalt layered double hydroxide (CCCH@NiCo‐LDH) core–shell nanowire arrays (NWAs) on Cu fibers with highly conductive Au‐modified CuO nanosheets (CCCH@NiCo‐LDH NWAs@Au–CuO/Cu) via a novel in situ corrosion growth method. This multicomponent hierarchical structure contributes to a large accessible surface area, which results in sufficient permeation of the electrolyte. The Cu dopant could reduce the work function and facilitate fast charge transfer kinetics. Therefore, the effective ion diffusion and electron conduction will facilitate the electrochemical reaction kinetics of the electrode. Benefiting from this unique structure, the electrode delivers a high specific capacitance (1.97 F cm…

Abstract Electrocatalytic water‐splitting has gained a firm hold in the area of renewable hydrogen production owing to its integrative compatibility with intermittent energy sources. However, wide‐scale implementation of this technology demands discovery of new electrode materials that strike a good balance between efficiency, stability, and cost. In the pool of inexpensive electrodes capable of catalyzing hydrogen and oxygen evolution reactions, metal borides/borates have made a big splash in the last decade. However, the research in this family of electrocatalysts remains unorganized owing to the diversity of reports. This review summarizes the past and present research progress in metal borides/borates for electrocatalytic water‐splitting. The fundamental reasons for electrochemical behavior in different metal borides/borates are highlighted here, also including some comments regarding erroneous practices in the performance evaluation of metal borides/borates. Various strategies used to enhance the electrocatalytic performance of metal borides/borates are discussed in detail.…

Abstract Electronic skin (e‐skin) technology is an exciting frontier to drive the next generation of wearable electronics owing to its high level of wearability, enabling high accuracy to harvest information of users and their surroundings. Recently, biomimicry of human and biological skins has become a great inspiration for realizing novel wearable electronic systems with exceptional multifunctionality as well as advanced sensory functions. This review covers and highlights bioinspired e‐skins mimicking perceptive features of human and biological skins. In particular, five main components in tactile sensation processes of human skin are individually discussed with recent advances of e‐skins that mimic the unique sensing mechanisms of human skin. In addition, diverse functionalities in user‐interactive, skin‐attachable, and ultrasensitive e‐skins are introduced with the inspiration from unique architectures and functionalities, such as visual expression of stimuli, reversible adhesion, easy deformability, and camouflage, in biological skins of natural creatures. Furthermore,…

Abstract There is an increasing demand for specialized pressure sensors in various applications. Previously, capacitive pressure sensors have been shown to have wide versatility in use, with a high degree of potential tuning possible through manipulating the geometry or material selection of the dielectric layer. However, in order to make sensors that are tunable and predictable, the design and fabrication method first needs to be developed. Presented here is an improved fabrication method to achieve tunable, consistent, and reproducible pressure sensors by using a pyramid microstructured dielectric layer along with a lamination layer. The as‐produced sensor performance is able to match predicted trends. Further, a simple model based on this system is developed and its efficacy is experimentally confirmed. Then, the model to predict a wide range of material and microstructure geometric properties prior to device fabrication is used to provide trends on sensor performance. Finally, it is demonstrated that the new method can be used to targetedly design a pressure sensor for a…

Abstract Thermal energy storage technologies based on phase‐change materials (PCMs) have received tremendous attention in recent years. These materials are capable of reversibly storing large amounts of thermal energy during the isothermal phase transition and offer enormous potential in the development of state‐of‐the‐art renewable energy infrastructure. Thermal conductivity plays a vital role in regulating the thermal charging and discharging rate of PCMs and improving the heat‐utilization efficiency. The strategies for tuning the thermal conductivity of PCMs and their potential energy applications, such as thermal energy harvesting and storage, thermal management of batteries, thermal diodes, and other forms of energy utilization, are summarized systematically. Furthermore, a research perspective is given to highlight emerging research directions of engineering advanced functional PCMs for energy applications.

Abstract Currently, development of suitable cathode materials for zinc‐ion batteries (ZIBs) is plagued by the sluggish kinetics of Zn2+ with multivalent charge in the host structure. Herein, it is demonstrated that interlayer Mn2+‐doped layered vanadium oxide (Mn0.15V2O5·nH2O) composites with narrowed direct bandgap manifest greatly boosted electrochemical performance as zinc‐ion battery cathodes. Specifically, the Mn0.15V2O5·nH2O electrode shows a high specific capacity of 367 mAh g−1 at a current density of 0.1 A g−1 as well as excellent retentive capacities of 153 and 122 mAh g−1 after 8000 cycles at high current densities up to 10 and 20 A g−1, respectively. Even at a low temperature of −20 °C, a reversible specific capacity of 100 mAh g−1 can be achieved at a current density of 2.0 A g−1 after 3000 cycles. The superior electrochemical performance originates from the synergistic effects between the layered nanostructures and interlayer doping of Mn2+ ions and water molecules, which can enhance the electrons/ions transport kinetics and structural stability during cycling. With…

Abstract Polymeric semiconductors have demonstrated great potential in the mass production of low‐cost, lightweight, flexible, and stretchable electronic devices, making them very attractive for commercial applications. Over the past three decades, remarkable progress has been made in donor–acceptor (D–A) polymer‐based field‐effect transistors, with their charge‐carrier mobility exceeding 10 cm 2 V −1 s −1 . Numerous molecular designs of D–A polymers have emerged and evolved along with progress in understanding the charge transport physics behind their high mobility. In this review, the current understanding of charge transport in polymeric semiconductors is covered along with significant features observed in high‐mobility D–A polymers, with a particular focus on polymeric microstructures. Subsequently, emerging molecular designs with further prospective improvements in charge‐carrier mobility are described. Moreover, the current issues and outlook for future generations of polymeric semiconductors are discussed.

Abstract Solution processing, including printing technology, is a promising technique for oxide thin‐film transistor (TFTs) fabrication because it tends to be a cost‐effective process with high composition controllability and high throughput. However, solution‐processed oxide TFTs are limited by low‐performance and stability issues, which require high‐temperature annealing. This high thermal budget in the fabrication process inhibits oxide TFTs from being applied to flexible electronics. There have been numerous attempts to promote the desired electrical characteristics of solution‐processed oxide TFTs at lower fabrication temperatures. Recent techniques for achieving low‐temperature (<350 °C) solution‐processed and printed oxide TFTs, in terms of the materials, processes, and structural engineering methods currently in use are reviewed. Moreover, the core techniques for both n‐type and p‐type oxide‐based channel layers, gate dielectric layers, and electrode layers in oxide TFTs are addressed. Finally, various multifunctional and emerging applications based on low‐temperature…

Abstract The catalytic conversion of CO 2 into valuable fuels is a compelling solution for tackling the global warming and fuel crisis. Light absorption and charge separation, as well as adsorption/activation of CO 2 on the photocatalyst surface, are essential steps for this process. This article reviews the CO 2 photoreduction mechanisms and critical aspects that greatly affect the photoreduction efficiency. Additionally, different materials for CO 2 photoreduction are provided, including d 0 and d 10 metal oxides/mixed oxides, sulfides, polymeric materials, and metal phosphides with visible response, metal‐organic frameworks, and layer double hydroxides. Furthermore, various structural engineering strategies and corresponding state‐of‐the‐art photocatalytic systems are reviewed and discussed, such as bandgap engineering, geometrical nanostructure engineering, and heterostructure engineering. Each strategy has advantages and disadvantages, requiring further adjustment to further improve the photocatalytic performance of the photocatalyst. Based on this review, it is greatly…

Abstract As an intermediate step during energy usage, supercapacitors with superior power density, long‐term cycling stability, and moderate energy density have attracted immense interest as a facile route to use energy in a clean, efficient, and versatile manner in smart grid applications, as well as portable devices and other applications. Currently, the major drawback of supercapacitors is the low energy density. Electrode materials are the key components determining the cell performance. Great research efforts are made to develop nanostructured electrode materials with high performance. On the other hand, integrating supercapacitors with other applications have led to the emergence of many new types of multifunctional supercapacitors, which are attractive for a myriad of applications. The current understanding on charge/discharge mechanisms of electric double layer capacitors and pseudo‐capacitors is discussed along with recent development in designing nanostructured electrode materials by structure/morphology engineering, doping, and crystal structure controlling. Achievements…

Abstract Most photocrosslinkable hydrogels have inadequacy in either mechanical performance or biodegradability. This issue is addressed by adopting a novel hydrogel design by introducing two different chitosan chains (catechol‐modified methacryloyl chitosan, CMC; methacryloyl chitosan, MC) via the simultaneous crosslinking of carbon–carbon double bonds and catechol‐Fe 3+ chelation. This leads to an interpenetrating network of two chitosan chains with high crosslinking‐network density, which enhances mechanical performance including high compressive modulus and high ductility. The chitosan polymers not only endow the hydrogels with good biodegradability and biocompatibility, they also offer intrinsic antibacterial capability. The quinone groups formed by Fe 3+ oxidation and protonated amino groups of chitosan polymer further enhance antibacterial property of the hydrogels. Serving as one of the two types of crosslinking mechanisms, the catechol‐Fe 3+ chelation can covalently link with amino, thiol, and imidazole groups, which substantially enhance the hydrogel's adhesion to…

Abstract As the requirements and expectation for displays in society are growing, higher standards of the display technology are proposed, including wider color gamut, higher color purity, and higher resolution. The recent emergence of light‐emitting halide perovskites has come with numerous advantages, such as high charge‐carrier mobility, tunable emission wavelength, narrow emission linewidth, and intrinsically high photoluminescence quantum yield. Recent advancement of perovskite‐based light‐emitting diodes (PeLEDs) as a promising technology for next‐generation displays is reviewed. Here, how the attractive optical and electrical properties of perovskite materials can be translated into high PeLED performance are discussed, and working mechanisms and optimization approaches of both perovskite materials and the respective devices are analyzed. On the material side this includes the control of size and composition of perovskites grains and nanocrystals, surface and interface passivation, doping and alloying, while on the device side this includes the interfacial engineering and…

Abstract Lithium–sulfur batteries (LSBs) are regarded as a new kind of energy storage device due to their remarkable theoretical energy density. However, some issues, such as the low conductivity and the large volume variation of sulfur, as well as the formation of polysulfides during cycling, are yet to be addressed before LSBs can become an actual reality. Here, presented is a comprehensive overview illustrating the techniques capable of mitigating these undesirable problems together with the electrochemical performances associated to the different proposed solutions. In particular, the analysis is organized by separately addressing cathode, anode, separator, and electrolyte. Furthermore, to better understand the chemistry and failure mechanisms of LSBs, important characterization techniques applied to energy storage systems are reviewed. Similarly, considerations on the theoretical approaches used in the energy storage field are provided, as they can become the key tool for the design of the next generation LSBs. Afterward, the state of the art of LSBs technology is presented…

Abstract The excellent energy‐storage performance of ceramic capacitors, such as high‐power density, fast discharge speed, and the ability to operate over a broad temperature range, gives rise to their wide applications in different energy‐storage devices. In this work, the (Pb 0.98 La 0.02 )(Zr 0.55 Sn 0.45 ) 0.995 O 3 (PLZS) antiferroelectric (AFE) ceramics are prepared via a unique rolling machine approach. The field‐induced multiphase transitions are observed in polarization–electric field (P–E) hysteresis loops. All the PLZS AFE ceramics possess high energy‐storage densities and discharge efficiency (above 80%) with different sintering temperatures. Of particular significance is that an ultrahigh recoverable energy‐storage density of 10.4 J cm ‐3 and a high discharge efficiency of 87% are achieved at 40 kV mm ‐1 for PLZS ceramic with a thickness of 0.11 mm, sintered at 1175 °C, which are by far the highest values ever reported in bulk ceramics. Moreover, the corresponding ceramics exhibit a superior discharge current density of 1640 A cm ‐2 and ultrafast discharge speed (75 ns…