With the rapid development of conductive polymers, they have shown great potential in room-temperature chemical gas detection, as their electrical conductivity can be changed upon exposure to oxidative or reductive gas molecules at room temperature. However, due to their relatively low conductivity and high affinity toward volatile organic compounds and water molecules, they always exhibit low sensitivity, poor stability, and gas selectivity, which hinder their practical gas sensor applications. In addition, inorganic sensitive materials show totally different advantages in gas sensors, such as high sensitivity, fast response to low concentration analytes, high surface area, and versatile surface chemistry, which could complement the conducting polymers in terms of the sensing characteristics. It seems to be a win-win choice to combine inorganic sensitive materials with polymers for gas detection due to their synergistic effects, which has attracted extensive interests in gas-sensing applications. In this review, we summarize the recent development in polymer-inorganic nanocomposite based gas sensors. The roles of inorganic nanomaterials in improving the gas-sensing performances of conducting polymers are introduced and the progress of conducting polymer-inorganic nanocomposites including metal oxides, metal, carbon (carbon nanotube, graphene), and ternary composites are presented. Finally, a conclusion and a perspective in the field of gas sensors incorporating conducting polymer-inorganic nanocomposite are summarized. Graphical Abstract

Fully integrated ultrathin, transparent and foldable energy storage devices are essential for the development of smart wearable electronics, yet typical supercapacitor electrodes are substrate-supported which limits their thickness, transparency and mechanical properties. Employing freestanding transparent electrodes with no substrate support could bring ultrathin, foldable and designable supercapacitors closer to reality. Herein, we report a freestanding, ultrathin (<5 μm), highly conductive (3 × 10⁴ S cm⁻¹), highly transparent (>84% transmittance) and foldable metallic network electrode, loaded with MnO₂ by electrochemical deposition, as a supercapacitor electrode. The freestanding metallic network electrode is fabricated via a simple and low-cost laser direct-writing micro-patterning technique followed by a selective electrodeposition process, where the metallic network patterns, network periods, metal thickness and also the electrode film patterns can be designed for different applications. The obtained freestanding MnO₂@Ni network electrode delivers an outstanding areal capacitance of 80.7 mF cm⁻² and long-term performance stability (96.3% after 10 000 cycles). Moreover, the symmetric solid-state supercapacitors employing the freestanding MnO₂@Ni network electrode not only show high areal capacitance as well as high optical transparency (>80% transmittance), but also can be tailored, attached, folded, rolled up, and crumpled into any object or various shapes with only slight performance degradation. The advent of such freestanding transparent metallic network electrodes may open up a new avenue for realizing fully integrated ultrathin, foldable and designable supercapacitors towards self-powered wearable electronics.

2D MXenes are highly attractive for achieving ultrafast and stable lithium/sodium storage due to their good electric conductivity and abundant redox active sites. While, effective strategies for scalable preparation of oligolayered MXenes are still under exploration. Herein, oligolayered Ti₃C₂T_x MXene is successfully obtained after conventional synthesis of multilayered Ti₃C₂ and subsequent delamination process via an organic solvent of tetramethyl-ammonium hydroxide (TMAOH). Comprehensive electrochemical study reveals that surface-controlled redox reaction dominated the charge storage behavior of oligolayered Ti₃C₂T_x with fast reaction kinetics. Impressively, the obtained oligolayered Ti₃C₂T_x exhibits excellent lithium/sodium storage performance, featured for a high specific capacity of 330 mAhg⁻¹ at 1.0 Ag⁻¹ after 800 cycles for lithium storage and 280 mAhg⁻¹ at 0.5 Ag⁻¹ after 500 cycles for sodium storage. Such impressive performance will advance the development of oligolayered Ti₃C₂T_x based materials for lithium/sodium storage and even broaden their application into energy storage.

Compact, transparent and flexible 5G multiple-input multiple-output (MIMO) and millimeter wave (mmW) array antennas with Ni-based embedded metallic mesh (EMM) nanotechnology are presented for the next-generation wireless communication in emerging applications, such as smart wearable devices, vehicle radars, and smart 5G remote devices. The EMM has the advantages of high conductivity, superior transparency, and mechanical stability. To simultaneously enhance the transparency and radiation efficiency, the selected structures of EMM are proposed and analyzed. The designed 5G MIMO antenna based on the EMM exhibits superior transparency of 93%, optimal radiation efficiency up to 85%, isolation above 20 dB, envelope correlation coefficient (ECC) under 0.005, and operation in 5G n79 band (4.4~5 GHz). The measured results are in good agreement with the simulated results. In addition, transparent and flexible 5G mmW arrays with a maximum gain of 9.6 dBi and scanning angle of approximately ± 75° are demonstrated in the 26 GHz and 28 GHz bands.