Guoqing Zu

Imine‐linked covalent organic frameworks (COFs) have wide applications in molecular separation, gas storage, photocatalysis, electrocatalysis, energy storage, and optoelectronic devices because of their unique advantages such as good crystallinity, permanent porosity, and tunable pore structure. However, the practical applications of imine‐linked COFs in chemical catalysis and gas separation may be hindered due to their reduced chemical stability in acidic or basic conditions. Recently, various effective strategies have been developed to improve chemical stability of imine‐linked COFs. In this review, we summarize the important advances in improving the stability of imine‐linked COFs from the viewpoint of design strategies, including electron‐donating group substitution, steric tuning, fluorine substitution, redox conversion, six‐membered cyclization, five‐membered cyclization, and so on. Moreover, the challenges and perspectives are also described to promote the realization of stable imine‐linked COFs, which will meet the requirements of these materials in practical applications.

Imine‐linked covalent organic frameworks (COFs) have wide applications in molecular separation, gas storage, photocatalysis, electrocatalysis, energy storage, and optoelectronic devices because of their unique advantages such as good crystallinity, permanent porosity, and tunable pore structure. However, the practical applications of imine‐linked COFs in chemical catalysis and gas separation may be hindered due to their reduced chemical stability in acidic or basic conditions. Recently, various effective strategies have been developed to improve chemical stability of imine‐linked COFs. In this review, we summarize the important advances in improving the stability of imine‐linked COFs from the viewpoint of design strategies, including electron‐donating group substitution, steric tuning, fluorine substitution, redox conversion, six‐membered cyclization, five‐membered cyclization, and so on. Moreover, the challenges and perspectives are also described to promote the realization of stable imine‐linked COFs, which will meet the requirements of these materials in practical applications.

Self‐powered flexible electronic skins (e‐skins) are promising for sustainable wearable electronics. Aerogels have emerged as attractive sensing platforms for flexible e‐skins because of their high porosity, lightweight, and tunable electrical properties. However, the current self‐powered aerogel‐based e‐skins usually show poor stretchability as well as limited sensitivity and functionality. Here, we report a new kind of bioinspired high‐performance e‐skins—stretchable multi‐modal electrochemical type self‐powered aerogel‐based e‐skins capable of detecting pressure, gas, and temperature without interfering with each other. The device integrates vanadium pentoxide hollow microsphere/MXene‐based aerogel cathode and carbon nanotube/MXene‐based aerogel anode with poly (ionic liquid) ionogel electrolyte, achieving battery‐type self‐powered pressure and chemical sensing. The multi‐modal self‐powered aerogel‐based e‐skins combine high pressure sensitivity (60.83 kPa ⁻¹ ), low pressure detection limit (1.5 Pa), low NH ₃ detection limit (0.5 ppm), temperature sensing, reversible stretchability (30%), tensile strain insensitivity, and the capability of detecting both static and dynamic signals. This work offers a versatile multifunctional platform as next‐generation high‐performance stretchable electronics promising for e‐skins, human‐computer interfaces, health monitoring, and soft robots.

Stretchable and recyclable organic electrochemical transistors (OECTs) have emerged as a promising platform for flexible and green electronics. However, stretchable OECTs and OECT‐based sensors usually show limited transconductance and sensitivity. Herein, stretchable, recyclable, high‐transconductance, and multifunctional OECTs based on nanoporous semiconducting polymer aerogels are developed. The flexible nanoporous structures (pore size ≈ 10–160 nm) effectively facilitate ion penetration/transport and doping of semiconductor, significantly enhancing transconductance of the stretchable OECTs and sensitivity of the OECT‐based sensors. The resulting OECT achieves a high transconductance of 27.4 mS and high stretching stability. Notably, both the semiconducting aerogel and substrate are recyclable, achieving the recyclability of the OECTs. It is demonstrated that the stretchable nanoporous aerogel OECTs can be used as platforms for various applications, including ultrasensitive stretchable biosensors for monitoring trace amount of biomarkers in biological fluids, stretchable tactile electronic skins with an ultralow detection limit (0.5 Pa), and artificial synapses for neuromorphic simulation. This work provides a versatile strategy toward stretchable nanoporous semiconducting polymers promising for sustainable, stretchable, and highly sensitive electronics.

Recyclable organic electronics such as organic electrochemical transistors (OECTs) show great potential for sustainable bioelectronics and sensors. However, it is challenging to achieve recyclability of the OECTs, and the reported active layers of the OECTs typically feature dense semiconductor films with limited ion permeation/transport. Here, recyclable and flexible OECTs based on nanoporous aramid nanofibers/semiconducting polymer aerogels are developed. The resulting OECTs exhibit significantly enhanced ion permeation and transport and record-high transconductance of 136.5 mS among the OECTs with similar channel sizes. The aerogel OECT-based microfluidic dual-channel biosensor shows record-low detection limits of 10 and 1 pM in response to lactate and lysozyme, respectively, making it capable of identifying trace amounts of biomarkers in real body fluids such as saliva and tear. In addition, the semiconducting aerogels are recyclable, offering the possibility of reuse of the transistors. This work presents a powerful approach to recyclable semiconductor aerogels and ultrasensitive OECT biosensors for wearable/sustainable applications.

Stretchable organic electrochemical transistors (OECTs) are promising for flexible electronics. However, the balance between stretchability and electrical properties is a great challenge for OECTs. Here, high-performance stretchable all-gel OECTs based on semiconducting polymer gel active layers and poly(ionic liquid) ionogel electrolytes are developed. The all-gel network structures effectively promote ion penetration/transport and endows the OECTs with high stretchability. The resulting OECTs exhibit an excellent combination of ultra-high transconductance of 86.4 mS, on/off ratio of 1.2 × 10⁵, stretchability up to 50%, and high stretching stability up to 10000 cycles under 30% strain. We demonstrate that the all-gel OECTs can be used as stretchable pressure-sensitive electronic skins with a low detection limit for tactile perception of robotic hands. In addition, the all-gel OECTs can be applied as stretchable artificial synapses for neuromorphic simulation and highly sensitive stretchable gas sensors for simulating olfactory perception process and monitoring food quality. This work provides a general all-gel strategy toward high-performance flexible electronics.

The development of highly stretchable self‐powered electronic skins with a broad detection range is urgently needed but remains a great challenge. Herein, unprecedented highly stretchable, broad‐range‐response, supercapacitor‐type, one‐body, and self‐powered electronic skins are developed by assembling porous polyurethane/polypyrrole electrode, polyacrylic acid/polyacrylamide ionic gel electrolyte, and porous polyurethane/MXene electrode. The folded porous structure of the electrodes significantly enhances the stretchability, while the modulus‐gradient multilayer structure of the device effectively broadens the pressure detection range. The electronic skins combine self‐powered dynamic/static pressure sensing, ultrabroad detection range (20 Pa–3.5 MPa), ultrahigh stretchability up to 387%, excellent compression stability (5000 cycles under 195 kPa), and good stretching stability (500 cycles under 200% tensile strain). They have the capability of monitoring human body motions, physiological signals, and high pressures from motorcycle tires, as well as tactile sensing of robotic grippers. In addition, they can be applied for highly stretchable thermal management and electromagnetic shielding devices. This work provides a new strategy for the development of highly stretchable, broad‐range‐response, and multifunctional self‐powered wearable electronics and sensors.