SiO₂ aerogels possess low density, ultralow thermal conductivity and excellent chemical stability, endowing them suitable for wide application in the fields of aviation/aerospace, building energy conservation, and energy chemical industry. Traditional SiO₂ nanoparticle aerogels have large brittleness and poor resilience due to their pearl necklace-like particle structure. Using nanofibers as construction units to fabricate SiO₂ nanofiber aerogels can overcome these shortcomings to some extent. However, the resilience mechanism of SiO₂ nanofiber aerogels is still unclear, which limits further improvement in their mechanical properties. Here, flexible SiO₂ nanofibers were prepared by electrospinning to investigate the effect of calcination temperature on phase microstructure to elucidate flexibility mechanism. Subsequently, SiO₂ nanofiber aerogels were fabricated by freeze drying. The influence of solid content on the pore structure, strength and resilience of aerogels was studied. A buckling deformation model based on effective nanofiber length was established to explain the compressive resilience mechanism. The findings show that calcination temperature affects the amorphous structure and flexibility of SiO₂ nanofibers. Degree of short-range order in SiO₂ increases with the increase in calcination temperature, leading to poor flexibility of nanofibers, while resilience of SiO₂ nanofiber aerogels is related to solid content. The energy loss coefficient and resilient rate of the aerogels fabricated with 0.5% (in mass) solid content are 0.6 and 55.2%, respectively. Further data shows that the resilience of SiO₂ nanofiber aerogels is dominated by effective nanofiber length and the curvature radius of nanofibers. Based on the above results, a relationship of resilience model is established and proved through nanofiber buckling theory. With a reduction in curvature radius, achievable through enhancement of nanofiber flexibility and increase in effective nanofiber length, the compressive resilient rate of aerogels increases. The present study provides theoretical guidance for the design of SiO₂ nanofiber aerogels with high resilience.

Flexible thermoelectric devices, capable of generating electricity from the slight temperature difference between the human body and the environment, demonstrate significant potential for continuous power supply in wearable devices. However, the poor thermoelectric performance still limits their widespread application. This study reports a method for fabricating high-performance flexible thermoelectric thin films using inkjet printing. AgCuTe nanowires prepared by a chemical transfer method were dispersed in ethanol to form the ink with no significant sedimentation, which could be stably and continuously sprayed to print p-type thermoelectric films on polyimide substrates. Dense thermoelectric films were then obtained through thermal treatment by a spark plasma sintering furnace, and the effect of sintering temperature on thermoelectric properties was studied. The results showed that the film sintered at a pressure of 10 MPa and a temperature of 400 ℃ for 15 min possessed a room temperature power factor of 432 µW·m^-1·K^-2, which is 182% higher than that of inkjet-printed p-type Bi₂Te₃ films (a room temperature power factor of 153 µW·m^-1·K^-2) reported in literature. This advancement further expands the application of inkjet printing in the field of flexible thermoelectrics and provides more possibilities for the fabrication of a new generation of high-performance flexible thermoelectric devices.

As a kind of important functional material, flexible piezoelectric materials can realize the effective conversion between mechanical energy and electrical energy, with the advantages of good toughness, high plasticity and light weight. Therefore, they can be attached to the human body to obtain human or environment information in real time, which is widely used in the fields of motion detection, health monitoring, and human-computer interaction. Due to high requirements of various three-dimensional (3D) structures of the flexible piezoelectric materials, additive manufacturing has been extensively utilized to fabricate different kinds of piezoelectric materials. This technology is expected to break the bottleneck of traditional processing of piezoelectric material by improving the structural design freedom and the performance of flexible piezoelectric materials, and provides enormous potential and opportunities for the application of flexible piezoelectric materials. Based on the introduction of the classification and features of flexible piezoelectric materials, this paper explained the main additive manufacturing technologies, including fused deposition modeling, direct ink writing, selective laser sintering, electric-assisted direct writing, stereolithography, and inkjet printing that commonly used in processing these materials. Then, various structural designs, such as multi-layer structure, porous structure, and interdigital structure for the flexible piezoelectric materials produced by different additive manufacturing approaches were reviewed. Moreover, the applications of additive manufactured flexible piezoelectric materials in energy harvesting, piezoelectric sensing, human-computer interaction, and bioengineering were introduced. Finally, the challenges faced by additive manufacturing on processing flexible piezoelectric materials and the development trends in the future were summarized and prospected.

Recently, perovskite solar cells have developed marvelously of which power conversion efficiency (PCE) achieved 26.1%, but the mechanical bending and environmental stability of flexible perovskite solar cells (F-PSCs) have remained major obstacles to their commercialization. In this study, the quality and crystallization of perovskite thin films were enhanced by adding agarose (AG). The interaction mechanism, PCE, mechanical bending and environmental stability of the assembled F-PSCs were investigated. It was found that the perovskite films modified by the optimal concentration of AG (3 mmol/L) exhibited denser and smoother morphology, higher crystallinity and absorbance, the lowest defect state density, and lower charge transfer resistance of 2191 Ω. Based on the optimal photoelectric properties, PCE increased from 15.17% to 17.30%. TiO₂ nanoparticles (0.75 mmol/L) were further introduced to form a synergistic interaction with AG (3 mmol/L), which provided a rigid backbone structure, and thus enhanced the mechanical and environmental stability of perovskite layers. After 1500 cycles of bending (3 mm in radius), the AG/TiO₂ co-modified F-PSCs maintained 84.73% of initial PCE, much higher than the blank device (9.32%). After 49 d in the air, the optimal F-PSCs still maintained 83.27% of initial PCE, superior than the blank device (62.21%). This work provides possibility for preparing highly efficient and stable F-PSCs.

Developing novel low-dimensional materials for terahertz electromagnetic shielding and absorbing applications represents a critical research frontier. Their unique electrical, mechanical, and electromagnetic responses hold great potential in enabling more efficient solutions for electromagnetic shielding and absorbing. Two-dimensional transition metal carbides, nitrides, and carbonitride MXenes have already demonstrated excellent electromagnetic shielding and absorbing performance in the low-frequency spectrum. MXenes possess high conductivity, low density, and high flexibility, which are advantageous for future portability and integration of terahertz devices and systems. However, practical implementation of MXene-based terahertz electromagnetic shielding and absorption materials faces challenges in adhesion stability, environmental resilience, and high-temperature tolerance, hindering their suitability for aerospace and future next generation communication applications. Moreover, in terahertz frequency band, lacking more comprehensive and reliable electromagnetic scattering and absorbing measurement methods limits the development of THz shielding and absorbing materials. Extensive research efforts have targeted on these limitations, exploring fundamental architectural and theoretical aspects of prevalent electromagnetic materials. This review specifically highlights the terahertz electromagnetic shielding and absorption characteristics inherent in various MXenes and their compositions, such as Ti₃C₂T_x, Mo₂Ti₂C₃T_x, Mo₂TiC₂T_x, Nb₄C₃T_x, and Nb₂CT_x. Additionally, this review envisages the forthcoming challenges and prospects of MXenes as a pivotal electromagnetic shielding and absorbing material within the terahertz frequency band.

In recent years, pressure sensors have been widely applied in the fields of smart wearable textile, health detection, and electronic skin. The emergence of the two-dimensional nanomaterial MXene has brought a brand-new breakthrough for pressure sensing. Ti₃C₂T_x is the most popular studied MXene in the field of pressure sensing and shows good mechanical, electrical properties, excellent hydrophilicity, and extensive modifiability, enabling it an ideal material for pressure sensing. Hence, researchers have conducted a lot of explorations and studies on design and application of MXene in pressure sensors in recent years. Herein, the preparation technologies and antioxidant methods are summarized. Design of MXene-based microstructures is also introduced, including aerogels/porous structural materials, hydrogels, flexible substrates, and films, which are beneficial to improve the response range, sensitivity, and flexibility of pressure sensors, and promote the rapid development of pressure sensors. The mechanisms of MXene pressure sensors are further broached, including piezoresistive, capacitive, piezoelectric, triboelectric, battery typed and nanofluidic. MXene has been applied in a wide range of sensors for various mechanisms due to its excellent characteristics. Finally, the chance and challenge in the synthesis, properties, and pressure sensing performance of MXene materials are prospected.

Two-dimensional (2D) transition metal carbides/nitrides (MXenes), since their discovery in 2011, have attracted great attention in the fields of energy storage, catalysis, sensors, electromagnetic interference shielding and microwave absorption and so on, owing to their special 2D layered structure, excellent electrical conductivity and electrochemical properties. In recent years, with the deep understanding of MXenes, the research on the realm related to optoelectronic properties has been widely concerned. Unlike other application fields, optoelectronic devices based on MXenes focus on extending semiconductor properties, including tunable band gap of the MXenes via design of the surface functional groups and layer control, etc., so as to achieve their transformation from metal to semiconductor properties. This paper revolves around the photoelectric properties of MXenes, mainly introduce its application in flexible optoelectronic devices, and systematically describe their current status and trend in transparent electronic devices, photodetectors, image sensors, transistors, and artificial neural vision network systems. The challenges and future development prospects of MXenes-based flexible optoelectronic devices are also proposed.

Flexible sensors have wide applications in various fields such as biomedicine, environmental monitoring and smart wearable devices, as they can adapt to diverse complex environments and curved surfaces. This study aimed to develop resilient and flexible oxygen sensors based on fluorescence quenching. A flexible oxygen sensing component was prepared, comprising aluminum silicate fibers as the support, polydimethysiloxane (PDMS) as the matrix, and platinum tetrakis pentafluorophenyl porphyrin (PtTFPP) as the oxygen probe. The component exhibited superhydrophobicity with a water contact angle of 152°, which was beneficial for maintaining integrity in humid atmospheres and aqueous solutions. It showed the fluorescence quenching effect towards gaseous oxygen and dissolved oxygen in water, which could be well fitted by the Stern-Volmer equation with K_SV constants of 0.020 h·Pa^-1 for the gaseous oxygen and 2.94 L·mmol^-1 for the dissolved oxygen. The component also demonstrated good reversibility and fast response in rapidly altered atmosphere, with a response time of 0.9 s from nitrogen switching to oxygen and a recovery time of 2.7 s from oxygen switching to nitrogen. Additionally, the PtTFPP-PDMS component displayed remarkable stability concerning its relative fluorescence intensity and water contact angle even after exposure to 100 ℃ steam for 15 h, soaking in pH 1-10 aqueous solutions, and enduring 400 bending cycles. The aluminum silicate fiber-supported PtTFPP-PDMS film developed in this study exhibited excellent fluorescent oxygen sensing properties and stability, making it a promising candidate for oxygen sensors, and suitable for determination of gaseous and dissolved oxygen in challenging environments.

Selenium (Se) is considered as a new generation energy storage material of lithium-selenium (Li-Se) battery due to its high volume specific capacity (3253 mAh·cm^-3) and high electronic conductivity (1×10^-5 S·m^-1). To address the problems of volume expansion, fast capacity decay, and low utilization of active materials during its charging-discharging process, a ZIF-L derived nitrogen-doped nanosheets/selenium (Se@NC/CC) flexible self-supported composite electrode is designed in this study for lithium-selenium battery by growing two-dimensional zinc-based metallic organic framework (ZIF-L) on carbon cloth (CC). The rich microporous structure in the nitrogen-doped carbon nanosheets can effectively alleviate the volume expansion during the reaction process, and the doping of heteroatoms N helps to adsorb Li₂Se and reduce the loss of active substances. In particular, it is found that there is strong chemical bonding between Se and C in the Se@NC/CC electrode, which also helps to reduce the loss of active materials and improve the performance. Electrochemical results show that the initial discharge specific capacity of the Se@NC/CC electrode is 574 mAh·g^-1 at a current density of 0.5C (1.0C=675 mAh·g^-1), demonstrating a high initial discharge specific capacity. At a current density of 2.0C, the initial discharge specific capacity is 453.3 mAh·g^-1, which maintains at 406.2 mAh·g^-1 after cycling for 500 cycles and it also displays excellent rate performance compared to literature. Such a flexible self-supported selenium cathode designed in this study provides a new research route on the design of selenium host materials for advanced alkali metal-selenium batteries.