Ultrathin, soft, flexible and stretchable sensors offer good opportunity to design personal health diagnosis and treatment systems by fabricating wearable biomedical devices for continuous health ...monitoring and preventive medicine. This paper summarizes the recent advances of flexible sensors for next generation biomedical applications. Materials used for flexible sensors are first briefly introduced. Followed to this part, the latest developments of flexible sensors for biomedical applications are discussed in detail, including flexible sensors for skin-attached devices and implantable devices. Finally, the challenges and future research directions of flexible sensors are also discussed in the development of biomedical devices.
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For the mimicry of human visual memory, a prominent challenge is how to detect and store the image information by electronic devices, which demands a multifunctional integration to sense light like ...eyes and to memorize image information like the brain by transforming optical signals to electrical signals that can be recognized by electronic devices. Although current image sensors can perceive simple images in real time, the image information fades away when the external image stimuli are removed. The deficiency between the state‐of‐the‐art image sensors and visual memory system inspires the logical integration of image sensors and memory devices to realize the sensing and memory process toward light information for the bionic design of human visual memory. Hence, a facile architecture is designed to construct artificial flexible visual memory system by employing an UV‐motivated memristor. The visual memory arrays can realize the detection and memory process of UV light distribution with a patterned image for a long‐term retention and the stored image information can be reset by a negative voltage sweep and reprogrammed to the same or an other image distribution, which proves the effective reusability. These results provide new opportunities for the mimicry of human visual memory and enable the flexible visual memory device to be applied in future wearable electronics, electronic eyes, multifunctional robotics, and auxiliary equipment for visual handicapped.
An artificial flexible visual memory system based on a UV‐motivated memristor is assembled by integrating light‐sensitive imaging sensors and resistance‐switching memristors. Sensing and memory abilities toward UV light are realized and the visual memory arrays successfully realize the detection and memory process of light distribution with a patterned image for a long‐term retention, thus providing new opportunities for the mimicry of human visual memory and enabling the flexible visual memory device to be applied in future wearable electronics, electronic eyes, multifunctional robotics, etc.
Flexible electronics have gained considerable research interest in the recent years because of their special features and potential applications in flexible displays, artificial skins, sensors, ...sustainable energy,
etc.
With unique geometry, outstanding electronic/optoelectronic properties, excellent mechanical flexibility and good transparency, inorganic nanowires (NWs) offer numerous insights and opportunities for flexible electronics. This article provides a comprehensive review of the inorganic NW based flexible electronics studied in the past decade, ranging from NWs synthesis and assembly to several important flexible device and energy applications, including transistors, sensors, display devices, memories and logic gates, as well as lithium ion batteries, supercapacitors, solar cells and generators. The integration of various flexible nanodevices into a self-powered system was also briefly discussed. Finally, several future research directions and opportunities of inorganic NW flexible and portable electronics are proposed.
This review summarizes the latest research for exploiting the flexible electronic applications of inorganic nanowires.
Hydrogen production via water electrocatalysis is limited by the sluggish anodic oxygen evolution reaction (OER) that requires a high overpotential. In response, a urea‐assisted energy‐saving ...alkaline hydrogen‐production system has been investigated by replacing OER with a more oxidizable urea oxidation reaction (UOR). A bimetal heterostructure CoMn/CoMn2O4 as a bifunctional catalyst is constructed in an alkaline system for both urea oxidation and hydrogen evolution reaction (HER). Based on the Schottky heterojunction structure, CoMn/CoMn2O4 induces self‐driven charge transfer at the interface, which facilitates the absorption of reactant molecules and the fracture of chemical bonds, therefore triggering the decomposition of water and urea. As a result, the heterostructured electrode exhibits ultralow potentials of −0.069 and 1.32 V (vs reversible hydrogen electrode) to reach 10 mA cm−2 for HER and UOR, respectively, in alkaline solution, and the full urea electrolysis driven by CoMn/CoMn2O4 delivers 10 mA cm−2 at a relatively low potential of 1.51 V and performs stably for more than 15 h. This represents a novel strategy of Mott–Schottky hybrids in electrocatalysts and should inspire the development of sustainable energy conversion by combining hydrogen production and sewage treatment.
A Schottky catalyst is constructed from a CoMn/CoMn2O4 heterostructure for energy‐saving hydrogen production from alkaline solution via urea electrocatalysis. Benefiting from the interface electron redistribution, CoMn/CoMn2O4 can synergistically facilitate the adsorption and fracture of the chemical groups in urea and water molecules and thus promote urea electrocatalysis.
Materials engineering plays a key role in the field of electrochemical energy storage, and considerable efforts have been made in recent years to fulfil the future requirements of electrochemical ...energy storage using novel functional electrode materials. Among the transition metal oxides, ternary metal oxides possess multiple oxidation states that enable multiple redox reactions. They have been reported to exhibit a higher supercapacitive performance than single component metal oxides, and seem to be a group of the most promising and low cost materials for pseudo-capacitors. This paper presents a state-of-the-art review on the research progress of developing ternary oxide nanostructures for supercapacitors, with the focus on the synthesis of one-dimensional (1-D), two-dimensional (2-D) and three-dimensional (3-D) nanostructures and their potential applications in energy storage devices. The remaining challenges toward the rational design of ternary oxide nanostructured electrodes for next-generation supercapacitors are also proposed.
Materials engineering plays a key role in the field of electrochemical energy storage, and considerable efforts have been made in recent years to fulfil the future requirements of electrochemical energy storage using novel functional electrode materials.
Environmentally friendly biomimetic materials with good deformability, high pressure-sensitive performance, and excellent biocompatibility are highly attractive for health monitoring, but to ...simultaneously meet these requirements is a formidable challenge. In this study, biocompatible MXene quantum dot (MQD)/watermelon peel (WMP) aerogels were obtained by immersing freeze-dried fresh watermelon peel into the quantum dot dispersion. The resulting bio-aerogels with a three-dimensional (3D) porous network structure exhibited a low in elasticity modulus (0.03 MPa) and limit of detection (0.4 Pa) and it showed biocompatibility. With a maximum pressure-sensitive response of 323 kPa
−1
, the 3D porous MQD/WMP aerogels exhibited good stability. In addition, the sensing signals could be displayed on mobile phones through a Bluetooth module to monitor human motion (pulse, sound, and walking) in real time. More importantly, the MQD/WMP aerogels exhibited excellent biocompatibility in a cytotoxicity test, thus decreasing the safety risk when they are applied to human skin. The finding in this study will facilitate the fabrication of high-performance biomimetic MXene active matrices, which are derived from natural biological materials, for flexible electronics.
With the rapid expanse and progress of flexible/wearable electronics, it is highly desirable to develop flexible/stretchable power sources, as it is a key technique for the realization of fully ...flexible integrated systems. Lithium‐ion batteries (LIBs) are one of the most ideal candidates of power sources because of their attractive features of high energy density, high power density, and long cycle life. The recent progress of flexible/stretchable LIBs from the viewpoint of device structure design is reviewed herein, as the device configurations are vital for the practical applications of flexible/stretchable LIBs. The remaining challenges and future opportunities for this emerging field are also highlighted from the viewpoint of practical applications.
Device configurations are vital for the practical applications of flexible/stretchable lithium‐ion batteries, which affect the electrochemical performance, mechanical flexibility or stretchability, and practical applications. This review summarizes recent progress in the development of flexible/stretchable LIBs in terms of device configurations, and their applications in fully flexible/stretchable integrated systems.
Flexible energy‐storage devices are attracting increasing attention as they show unique promising advantages, such as flexibility, shape diversity, light weight, and so on; these properties enable ...applications in portable, flexible, and even wearable electronic devices, including soft electronic products, roll‐up displays, and wearable devices. Consequently, considerable effort has been made in recent years to fulfill the requirements of future flexible energy‐storage devices, and much progress has been witnessed. This review describes the most recent advances in flexible energy‐storage devices, including flexible lithium‐ion batteries and flexible supercapacitors. The latest successful examples in flexible lithium‐ion batteries and their technological innovations and challenges are reviewed first. This is followed by a detailed overview of the recent progress in flexible supercapacitors based on carbon materials and a number of composites and flexible micro‐supercapacitors. Some of the latest achievements regarding interesting integrated energy‐storage systems are also reviewed. Further research direction is also proposed to surpass existing technological bottle‐necks and realize idealized flexible energy‐storage devices.
Flexible energy‐storage devices are indispensable to the development of flexible electronics. This review surveys recent achievements, focusing on flexible lithium‐ion batteries and flexible supercapacitors combined with integrated energy‐storage systems.
In recent years, metal halide perovskites have been widely investigated to fabricate photodetectors for image sensing due to the excellent photoelectric performance, tunable bandgap, and low‐cost ...solution preparation process. In this review, a comprehensive overview of the recent advances in perovskite photodetectors for image sensing is provided. First, the key performance parameters and the basic device types of photodetectors are briefly introduced. Then, the recent developments of image sensors on the basis of different dimensional perovskite materials, including 0D, 1D, 2D, and 3D perovskite materials, are highlighted. Besides the device structures and photoelectric properties of perovskite image sensors, the preparation methods of perovskite photodetector arrays are also analyzed. Subsequently, the single‐pixel imaging of perovskite photodetectors and the strategies to fabricate narrowband perovskite photodetectors for color discrimination are discussed. Finally, the potential challenges and possible solutions for the future development of perovskite image sensors are presented.
Metal halide perovskites are widely investigated in photodetection applications due to their remarkable photoelectric properties. Herein, an overview of the recent advances in perovskite photodetectors for image sensing is provided. The device structures, preparation methods, and photoelectric properties of image sensors based on different dimensional perovskites are highlighted. The single‐pixel imaging and narrowband detection of perovskite photodetectors are also discussed.
Achieving high deformability in response to minimal external stimulation while maximizing human–machine interactions is a considerable challenge for wearable and flexible electronics applications. ...Various natural materials or living organisms consisting of hierarchical or interlocked structures exhibit combinations of properties (e.g., natural elasticity and flexibility) that do not occur in conventional materials. The interlocked epidermal–dermal microbridges in human skin have excellent elastic moduli, which enhance and amplify received tactile signal transport. Herein, we use the sensing mechanisms inspired by human skin to develop Ti3C2/natural microcapsule biocomposite films that are robust and deformable by mimicking the micro/nanoscale structure of human skinsuch as the hierarchy, interlocking, and patterning. The interlocked hierarchical structures can be used to create biocomposite films with excellent elastic moduli (0.73 MPa), capable of high deformability in response to various external stimuli, as verified by employing theoretical studies. The flexible sensor with a hierarchical and interlocked structure (24.63 kPa–1) achieves a 9.4-fold increase in pressure sensitivity compared to that of the planar structured Ti3C2-based flexible sensor (2.61 kPa–1). This device also exhibits a rapid response rate (14 ms) and good cycling reproducibility and stability (5000 times). In addition, the flexible pressure device can be used to detect and discriminate signals ranging from finger motion and human pulses to voice recognition.
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