In recent decades, flexible and wearable devices have been extensively investigated due to their promising applications in portable mobile electronics and human motion monitoring. MXene, a novel growing family of 2D nanomaterials, demonstrates superiorities such as outstanding electrical conductivity, abundant terminal groups, unique layered-structure, large surface area, and hydrophilicity, making it to be a potential candidate material for flexible and wearable devices. Numerous pioneering works are devoted to develop flexible MXene-based composites with various functions and designed structures. Therefore, the latest progress of the flexible MXene-based composites for wearable devices is summarized in this review, focusing on the preparation strategies, working mechanisms, performances, and applications in sensors, supercapacitors, and electromagnetic interference shielding materials. Moreover, the current challenges and future outlooks are also discussed.
Hydrogel electrolytes have high room-temperature conductivity and can be widely used in energy storage device. However, hydrogels suffer from the inevitable freezing of water at subzero temperatures, resulting in the diminishment of their conductivity and mechanical properties. How to achieve high conductivity without sacrificing hydrogels' flexibility at subzero temperature is an important challenge. To address this challenge, a new type of zwitterionic polymer hydrogel (polySH) electrolytes is fabricated. The anionic and cationic counterions on the polymer chains facilitate the dissociation of LiCl. The antifreezing electrolyte can be stretched to a strain of 325% and compressed to 75% at −40 °C and possesses an outstanding conductivity of 12.6 mS cm −1 at −40 °C. A direct hopping migration mechanism of hydrated lithium-ion through the channel of zwitterion groups is proposed. The polySH electrolyte-based-supercapacitor (SC) exhibits a high specific capacitance of 178 mF cm −2 at 60 °C and 134 mF cm −2 at −30 °C with a retention of 81% and 71% of the initial capacitance after 10 000 cycles, respectively. The overall merits of the electrolyte will open up a new avenue for advanced ionic conductors and energy storage device in practical applications.
Paper-based
substrates have been increasingly attractive in flexible
electronics technology as flexible support substrates due to their
advantages of availability, environmental friendliness (as disposable,
degradable, and renewable materials), and foldability. Hereby, a facile
method for installation of p-type and n-type semiconductor legs in
the thickness direction of a paper substrate was established. A transparent
paper-based thermoelectric generator prototype by impregnating the
paper with resin was then fabricated. The resulting transparent paper-based
thermoelectric generator with 10 thermocouples showed excellent mechanical
flexibility. The generator maintained a maximum voltage and an output
power of ∼8.3 mV and ∼10 nW, respectively, at a temperature
difference of 35 K after 1000 bending cycles. This work offers a promising
strategy for the development of paper-based thermoelectric generators
that are adaptable to a wide variety of complex curved surface heat
source. Therefore, the heat recovery efficiency in both human and
natural environments can be greatly improved.
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