A family of 2D transition metal carbides and nitrides known as MXenes has received increasing attention since the discovery of Ti3C2 in 2011. To date, about 30 different MXenes with well‐defined structures and properties have been synthesized, and many more are theoretically predicted to exist. Due to the numerous assets including excellent mechanical properties, metallic conductivity, unique in‐plane anisotropic structure, tunable band gap, and so on, MXenes rapidly positioned themselves at the forefront of the 2D materials world and have found numerous promising applications. Particular interest is devoted to applications in electrochemical energy storage, whereby 2D MXenes work either as electrodes, additives, separators, or hosts. This review summarizes recent advances in the synthesis, fundamental properties and composites of MXene and highlights the state‐of‐the‐art electrochemical performance of MXene‐based electrodes/devices. The progresses in the field of supercapacitors and Li‐ion batteries, Li‐S batteries, Na‐ and other alkali metal ion batteries are reviewed, and current challenges and new opportunities for MXenes in this surging energy storage field are presented. In the focus of interest is the possibility to boost device‐level performance, particularly that of rechargeable batteries, which are of utmost importance in future energy technologies. Very recently, the 2019 Nobel Prize in Chemistry was awarded to the inventors of the Li‐ion battery. For sure, this will provide an additional stimulation to study fundamental aspects of electrochemical energy storage.
An ultimate monolayer of 2D organic crystal can deliver high OTFT performance and be a clean system to investigate device physics.
the coincidence efficiency. This indicates that the solid angle controlled by the PET system and the efficiency of the intrinsic detector are greater. [11,12] More significantly, the Compton events in the pulse height spectrum are mainly caused by scattering in the scintillator. Therefore, these deficiencies can be avoided by lowering the threshold. However, the signal provided by Compton scattering quanta in adjacent crystals may be higher than the threshold, and thus may affect the position resolution and make it worse. In X-ray computed tomography (CT), the body is mainly irradiated continuously from multiple directions by fan-shaped X-rays, while attenuation profiles are recorded, and finally reconstructed from the cross-sectional view of the body. [13] This technology mainly uses complex scanning methods in the field of clinical practice. At present, the realized way of X-rays detector can be roughly divided into two types, direct and indirect. The former one directly absorbs incident X-rays, generates electronic signals through semiconductors or engenders chemical signals through thin films. [14-17] This method can directly convert X-rays into visible light without going through other processes. Therefore, an X-ray detector with a wide linear response range, fast pulse rise time, high-energy resolution, and spatial resolution can be obtained, which makes it copiously applied in X-ray detection. [18-21] However, X-ray detectors based on semiconductors face the challenges of high cost and low efficiency. In addition, although the film is cheap, it is difficult to apply in digital form, which may limit its further development. The latter one refers to the conversion of X-rays (in the highenergy radiation, in addition to X-rays, α, β, and γ rays are also included) into ultraviolet visible (UV) light through scintillators which can be further captured by optical devices. [22-24] It consists of a scintillator and an array photodiode (PD). In contrast, since the scintillator that converts X-rays indirectly is cheap, it is easier to implement in the industry than direct detectors, and has the characteristics of low cost and abundant options, stability, and flexible conversion rate. [25,26] At present, indirect X-ray detectors are widely used in ordinary flat panel X-ray detectors. Moreover, it can be flexibly combined with commercially mature sensor arrays (e.g., amorphous silicon PDs, thin film transistor arrays, photomultiplier tubes, complementary metal oxide semiconductors, silicon avalanche PDs, and X-ray imaging charge-coupled devices [CCD]), therefore, they have attracted more attention. Scintillator is a unique class of luminescent materials, which is extensively used in many fields such as nondestructive testing, medical imaging, space probes, etc. Compared with the disadvantages of traditional scintillator materials which have high cost, are fragile, have long response time and low spatial resolution disadvantages, metal halide perovskites are considered to be the most potential scintillator materials in ...
Ultraflexible transparent film heaters have been fabricated by embedding conductive silver (Ag) nanowires into a thin poly(vinyl alcohol) film (AgNW/PVA). A cold-pressing method was used to rationally adjust the sheet resistance of the composite films and thus the heating powers of the AgNW/PVA film heaters at certain biases. The film heaters have a favorable optical transmittance (93.1% at 26 Ω/sq) and an outstanding mechanical flexibility (no visible change in sheet resistance after 10 000 bending cycles and at a radius of curvature ≤1 mm). The film heaters have an environmental endurance, and there is no significant performance degradation after being kept at high temperature (80 °C) and high humidity (45 °C, 80% humidity) for half a year. The efficient Joule heating can increase the temperature of the film heaters (20 Ω/sq) to 74 °C in ∼20 s at a bias of 5 V. The fast-heating characteristics at low voltages (a few volts) associated with its transparent and flexibility properties make the poly(dimethylsiloxane)/AgNW/PVA composite film a potential candidate in medical thermotherapy pads.
An electriferous rotating cone is used as spinneret for the production of nanofibers (see image). It is demonstrated that the production rate by this novel approach is several thousand times higher than that by the single‐needle electrospinning technique. This novel technique may attract interest for other applications such as recycling expanded polystyrene, textiles, and filtration meshes.
It has been an outstanding challenge to achieve implantable energy modules that are mechanically soft (compatible with soft organs and tissues), have compact form factors, and are biodegradable (present for a desired time frame to power biodegradable, implantable medical electronics). Here, we present a fully biodegradable and bioabsorbable high-performance supercapacitor implant, which is lightweight and has a thin structure, mechanical flexibility, tunable degradation duration, and biocompatibility. The supercapacitor with a high areal capacitance (112.5 mF cm−2 at 1 mA cm−2) and energy density (15.64 μWh cm−2) uses two-dimensional, amorphous molybdenum oxide (MoOx) flakes as electrodes, which are grown in situ on water-soluble Mo foil using a green electrochemical strategy. Biodegradation behaviors and biocompatibility of the associated materials and the supercapacitor implant are systematically studied. Demonstrations of a supercapacitor implant that powers several electronic devices and that is completely degraded after implantation and absorbed in rat body shed light on its potential uses.
A simple procedure for preparing highly porous TiO 2 nanotubes is reported. The nanotubes were prepared in the form of a nonwoven mat by emulsion electrospinning a solution containing poly(vinyl pyrrolidone), titanium tetraisopropoxide and oil, followed by calcination in air at 500 C. The mixed crystalline material comprised anatase and rutile TiO 2 particles, whose diameters were about 11 nm and 21 nm, respectively. The highly porous TiO 2 nanotube membranes, which had large specific surface areas and excellent ratios of anatase phase to rutile phase, were shown to have excellent catalytic activities. Also the mixture of crystal forms improved the efficiency of photocatalysis because at the mixed interface electrons and holes are separated effectively. The new method for producing highly porous TiO 2 nanotubes is versatile and could be extended to the fabrication of various types of highly porous nanotubes.
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