Energy harvesting modules play an increasingly important role in the development of autonomous self‐powered microelectronic devices. MXenes (i.e., 2D transition metal carbide/nitride) have recently ...emerged as promising candidates for energy applications due to their excellent electronic conductivity, large specific surface area, and tunable properties. Herein, a perspective on using MXenes to harvest energy from various sources in the environment is presented. First, the characteristics of MXenes that facilitate energy capturing are systematically introduced and the preparation strategies of MXenes and their derived nanostructures tailored toward such applications are summarized. Subsequently, the harvesting mechanism of different energy sources (e.g., solar energy, thermoelectric energy, triboelectric energy, piezoelectric energy, salinity‐gradient energy, electrokinetic energy, ultrasound energy, and humidity energy) are discussed. Then, the recent progress of MXene‐based nanostructures in energy harvesting, as well as their applications, is introduced. Finally, opinions on the existing challenges and future directions of MXene‐based nanostructure for energy harvesting are presented.
The progress in employing MXenes in energy harvesting applications is summarized. Different energy sources, including solar, ultrasound, electrokinetic, salinity‐gradient, piezoelectric, triboelectric, thermoelectric, and humidity energy, are discussed separately. The future challenges and promising directions of MXene research for energy harvesting are presented.
Printed electronics are an important enabling technology for the development of low‐cost, large‐area, and flexible optoelectronic devices. Transparent conductive films (TCFs) made from ...solution‐processable transparent conductive materials, such as metal nanoparticles/nanowires, carbon nanotubes, graphene, and conductive polymers, can simultaneously exhibit high mechanical flexibility, low cost, and better photoelectric properties compared to the commonly used sputtered indium‐tin‐oxide‐based TCFs, and are thus receiving great attention. This Review summarizes recent advances of large‐area flexible TCFs enabled by several roll‐to‐roll‐compatible printed techniques including inkjet printing, screen printing, offset printing, and gravure printing using the emerging transparent conductive materials. The preparation of TCFs including ink formulation, substrate treatment, patterning, and postprocessing, and their potential applications in solar cells, organic light‐emitting diodes, and touch panels are discussed in detail. The rational combination of a variety of printed techniques with emerging transparent conductive materials is believed to extend the opportunities for the development of printed electronics within the realm of flexible electronics and beyond.
The recent advances of large‐area flexible transparent conductive films (TCFs) enabled by several roll‐to‐roll‐compatible printing techniques including inkjet printing, screen printing, offset printing, and gravure printing using emerging transparent conductive materials are summarized, with the hope of providing timely references for the fabrication of low‐cost/large‐area flexible TCFs and advancing the field of flexible electronics in general.
In the booming development of flexible electronics represented by electronic skins, soft robots, and human–machine interfaces, 3D printing of hydrogels, an approach used by the biofabrication ...community, is drawing attention from researchers working on hydrogel‐based stretchable ionotronic devices. Such devices can greatly benefit from the excellent patterning capability of 3D printing in three dimensions, as well as the free design complexity and easy upscale potential. Compared to the advanced stage of 3D bioprinting, 3D printing of hydrogel ionotronic devices is in its infancy due to the difficulty in balancing printability, ionic conductivity, shape fidelity, stretchability, and other functionalities. In this review, a guideline is provided on how to utilize the power of 3D printing in building high‐performance hydrogel‐based stretchable ionotronic devices mainly from a materials’ point of view, highlighting the systematic approach to balancing the printability, printing quality, and performance of printed devices. Various 3D printing methods for hydrogels are introduced, and then the ink design principles, balancing printing quality, printed functions, such as elastic conductivity, self‐healing ability, and device (e.g., flexible sensors, shape‐morphing actuators, soft robots, electroluminescent devices, and electrochemical biosensors) performances are discussed. In conclusion, perspectives on the future directions of this exciting field are presented.
Hydrogel ionotronics prepared via 3D printing have received intensive attention due to the combination of high biocompatibility, stimuli‐responsiveness, rapid prototyping, and delicated patterns. Herein, recent advances in 3D printed hydrogel devices are reviewed, highlighting strategies to enhance printing quality (printability, resolution, and shape fidelity), properties (elastic conductivity, and self‐healing ability), and performances of various ionotronic devices.
As of June 8, 2020, the global reported number of COVID-19 cases had reached more than 7 million with over 400 000 deaths. The household transmissibility of the causative pathogen, severe acute ...respiratory syndrome coronavirus 2 (SARS-CoV-2), remains unclear. We aimed to estimate the secondary attack rate of SARS-CoV-2 among household and non-household close contacts in Guangzhou, China, using a statistical transmission model.
In this retrospective cohort study, we used a comprehensive contact tracing dataset from the Guangzhou Center for Disease Control and Prevention to estimate the secondary attack rate of COVID-19 (defined as the probability that an infected individual will transmit the disease to a susceptible individual) among household and non-household contacts, using a statistical transmission model. We considered two alternative definitions of household contacts in the analysis: individuals who were either family members or close relatives, such as parents and parents-in-law, regardless of residential address, and individuals living at the same address regardless of relationship. We assessed the demographic determinants of transmissibility and the infectivity of COVID-19 cases during their incubation period.
Between Jan 7, 2020, and Feb 18, 2020, we traced 195 unrelated close contact groups (215 primary cases, 134 secondary or tertiary cases, and 1964 uninfected close contacts). By identifying households from these groups, assuming a mean incubation period of 5 days, a maximum infectious period of 13 days, and no case isolation, the estimated secondary attack rate among household contacts was 12·4% (95% CI 9·8–15·4) when household contacts were defined on the basis of close relatives and 17·1% (13·3–21·8) when household contacts were defined on the basis of residential address. Compared with the oldest age group (≥60 years), the risk of household infection was lower in the youngest age group (<20 years; odds ratio OR 0·23 95% CI 0·11–0·46) and among adults aged 20–59 years (OR 0·64 95% CI 0·43–0·97). Our results suggest greater infectivity during the incubation period than during the symptomatic period, although differences were not statistically significant (OR 0·61 95% CI 0·27–1·38). The estimated local reproductive number (R) based on observed contact frequencies of primary cases was 0·5 (95% CI 0·41–0·62) in Guangzhou. The projected local R, had there been no isolation of cases or quarantine of their contacts, was 0·6 (95% CI 0·49–0·74) when household was defined on the basis of close relatives.
SARS-CoV-2 is more transmissible in households than SARS-CoV and Middle East respiratory syndrome coronavirus. Older individuals (aged ≥60 years) are the most susceptible to household transmission of SARS-CoV-2. In addition to case finding and isolation, timely tracing and quarantine of close contacts should be implemented to prevent onward transmission during the viral incubation period.
US National Institutes of Health, Science and Technology Plan Project of Guangzhou, Project for Key Medicine Discipline Construction of Guangzhou Municipality, Key Research and Development Program of China.
As a thriving member of the 2D nanomaterials family, MXenes, i.e., transition metal carbides, nitrides, and carbonitrides, exhibit outstanding electrochemical, electronic, optical, and mechanical ...properties. They have been exploited in many applications including energy storage, electronics, optoelectronics, biomedicine, sensors, and catalysis. Compared to other 2D materials, MXenes possess a unique set of properties such as high metallic conductivity, excellent dispersion quality, negative surface charge, and hydrophilicity, making them particularly suitable as inks for printing applications. Printing and pre/post‐patterned coating methods represent a whole range of simple, economically efficient, versatile, and eco‐friendly manufacturing techniques for devices based on MXenes. Moreover, printing can allow for complex 3D architectures and multifunctionality that are highly required in various applications. By means of printing and patterned coating, the performance and application range of MXenes can be dramatically increased through careful patterning in three dimensions; thus, printing/coating is not only a device fabrication tool but also an enabling tool for new applications as well as for industrialization.
Recent progress in the deposition/patterning of MXenes through printing and coating methods is summarized, including issues that are related to the formulation of MXene inks (e.g., dispersion, stability, and tuning of physical–chemical and morphological properties), relevant printing/coating methods, and their applications in energy storage, electronics/optoelectronics, sensing, and actuation.
Abstract
The discovery of ferromagnetic two-dimensional van der Waals materials has opened up opportunities to explore intriguing physics and to develop innovative spintronic devices. However, ...controllable synthesis of these 2D ferromagnets and enhancing their stability under ambient conditions remain challenging. Here, we report chemical vapor deposition growth of air-stable 2D metallic 1T-CrTe
2
ultrathin crystals with controlled thickness. Their long-range ferromagnetic ordering is confirmed by a robust anomalous Hall effect, which has seldom been observed in other layered 2D materials grown by chemical vapor deposition. With reducing the thickness of 1T-CrTe
2
from tens of nanometers to several nanometers, the easy axis changes from in-plane to out-of-plane. Monotonic increase of Curie temperature with the thickness decreasing from ~130.0 to ~7.6 nm is observed. Theoretical calculations indicate that the weakening of the Coulomb screening in the two-dimensional limit plays a crucial role in the change of magnetic properties.
Printing image based on metasurface has attracted enormous research interests due to its subwavelength resolution, full‐color printing, and durable properties. Based on the spatially multiplexed ...pixels, the printing image using metasurface can be switched optically by altering the optical parameters, such as polarization and incident wavelength. However, such multiplexed pixel design has several problems, including the cross‐talk among different wavelengths, limitation to linear polarizations, and incapability for incident‐angle control. Here, a general method for pixel design, called the coherent pixel, which can overcome the problems and be used for multiple printing‐image switching controlled by arbitrary optical parameters (arbitrary incident angle, polarization, and wavelength) is proposed. Based on this coherent pixel, metasurface devices with novel functionalities can be realized, such as incident‐angle controlled and arbitrary polarization‐controlled printing images, which are not feasible with previous conventional pixel design method. The suitability and superiority of the coherent pixel for encryption application is also discussed. Such printing‐image switching controlled with arbitrary optical parameters should pave the way for various applications, including various functional switchable optical devices, image displays, and information encryption.
A coherent pixel design method is implemented for metasurface printing image switching under arbitrary optical conditions with different combinations of incident angle, polarization, and wavelength of light. Such a design not only stimulates metasurface devices with novel functionalities, such as incident‐angle controlled and helicity‐controlled printing images, but also enables encryption applications with improved security.
Stretchable self‐healing supercapacitors (SCs) can operate under extreme deformation and restore their initial properties after damage with considerably improved durability and reliability, expanding ...their opportunities in numerous applications, including smart wearable electronics, bioinspired devices, human–machine interactions, etc. It is challenging, however, to achieve mechanical stretchability and self‐healability in energy storage technologies, wherein the key issue lies in the exploitation of ideal electrode and electrolyte materials with exceptional mechanical stretchability and self‐healing ability besides conductivity. Conductive hydrogels (CHs) possess unique hierarchical porous structure, high electrical/ionic conductivity, broadly tunable physical and chemical properties through molecular design and structure regulation, holding tremendous promise for stretchable self‐healing SCs. Hence, this review is innovatively constructed with a focus on stretchable and self‐healing CH based electrodes and electrolytes for SCs. First, the common synthetic approaches of CHs are introduced; then the stretching and self‐healing strategies involved in CHs are systematically elaborated; followed by an explanation of the conductive mechanism of CHs; then focusing on CH‐based electrodes and electrolytes for stretchable self‐healing SCs; subsequently, application of stretchable and self‐healing SCs in wearable electronics are discussed; finally, a conclusion is drawn along with views on the challenges and future research directions regarding the field of CHs for SCs.
Conductive hydrogels (CHs) are a new class of soft functional materials that have recently found application in flexible energy storage devices such as batteries and supercapacitors (SCs). Herein, the promise of CHs in this emerging field is demonstrated through summarizing their roles as ideal electrode and electrolyte materials for stretchable and self‐healing SCs.
An extremely simple in situ self‐transformation methodology is developed to introduce pseudocapacitance into the MOF system resulting in a largely boosted electrochemical performance: a three‐fold ...increase in capacitance as well as improved rate capacity. An all‐solid‐state hybrid flexible supercapacitor is fabricated based on the obtained MnOx–MHCF composite and activated carbon with an areal capacitance of 175 mF cm−2 at 0.5 mA cm−2.
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