A hydrogen (H ) gas sensor based on a silicon (Si) nanomesh structure decorated with palladium (Pd) nanoparticles is fabricated via polystyrene nanosphere lithography and top-down fabrication processes. The gas sensor shows dramatically improved H gas sensitivity compared with an Si thin film sensor without nanopatterns. Furthermore, a buffered oxide etchant treatment of the Si nanomesh structure results in an additional performance improvement. The final sensor device shows fast H response and high selectivity to H gas among other gases. The sensing performance is stable and shows repeatable responses in both dry and high humidity ambient environments. The sensor also shows high stability without noticeable performance degradation after one month. This approach allows the facile fabrication of high performance H sensors via a cost-effective, complementary metal-oxide-semiconductor (CMOS) compatible, and scalable nanopatterning method.

MXenes have attracted great attention for their potential applications in electrochemical and electronic devices due to their excellent characteristics. Traditional sound sources based on the thermoacoustic effect demonstrated that a conductor needs to have an extremely low heat capacity and high thermal conductivity. Hence, a thin MXene film with a low heat capacity per unit area (HCPUA) and special layered structure is emerging as a promising candidate to build loudspeakers. However, the use of MXenes in a sound source device has not been explored. Herein, we have successfully prepared sound source devices on an anodic aluminum oxide (AAO) and a flexible polyimide (PI) substrates by using the prepared Ti3C2 MXene nanoflakes. Due to the larger interlayer distance of MXene, the MXene-based sound source device has a higher sound pressure level (SPL) than that of graphene of the same thickness. High-quality Ti3C2 MXene nanoflakes were fabricated by selectively etching the Ti3AlC2 powder. The as-fabricated MXene sound source device on an AAO substrate exhibits a higher SPL of 68.2 dB (f = 15 kHz) and has a very stable sound spectrum output with frequency varying from 100 Hz to 20 kHz. A theoretical model has been built to explain the mechanism of the sound source device on an AAO substrate, matching well with the experimental results. Furthermore, the MXene sound source device based on a flexible PI substrate has been attached to the arms, back of the hand, and fingers, indicating an excellent acoustic wearability. Then, the MXene film is packaged successfully into a commercial earphone case and shows an excellent performance at high frequencies, which is very suitable for human audio equipment.

This paper reports zinc oxide (ZnO)-coated piezoelectret polypropylene (PP) microfibers with a structure of two opposite arc-shaped braces for enhanced mechanical energy harvesting. The ZnO film was coated onto PP microfibers via magnetron sputtering to form a ZnO/PP compound structure. Triboelectric Nanogenerator (TENG) based on ZnO/PP microfiber compound film was carefully designed with two opposite arc-shaped braces. The results of this study demonstrated that the mechanical energy collection efficiency of TENG based on piezoelectret PP microfiber was greatly enhanced by the coated ZnO and high-voltage corona charging method. We found that, with the step-increased distance of traveling for the movable carbon black electrode, an electrical power with an approximately quadratic function of distance was generated by this mechanical-electrical energy conversion, because more PP microfibers were connected to the electrode. Further, with a full contact condition, the peak of the generated voltage, current, and charges based on the ZnO/PP microfibers by this mechanical-electrical energy conversion with 1 m/s reached 120 V, 3 μA, and 49 nC, respectively. Moreover, a finger-tapping test was used to demonstrate that the ZnO/PP microfiber TENG is capable of lighting eight light-emitting diodes.

Herein, a nanowelding technique is adopted to fabricate three-dimensional layer-by-layer Pd-containing nanocomposite structures with special properties. Nanowires fabricated from noble metals (Pd, Pt, Au, and Ag) were used to prepare Pd− Pd nanostructures and Pd−Au, Pd−Pt, Pd−Ag, and Pd−Pt−Au nanocomposite structures by controlling the welding temperature. The recrystallization behavior of the welded composite materials was observed and analyzed. In addition, their excellent mechanical and electrical properties were confirmed by performing 10,000 bending test cycles and measuring the resistances. Finally, flexible and wearable nanoheaters and gas sensors were fabricated using our proposed method. In comparison with conventional techniques, our proposed method can not only easily achieve sensors with a large surface area and flexibility but also improve their performance through the addition of catalyst metals. A gas sensor fabricated using the Pd−Au nanocomposites demonstrated 3.9-fold and 1.1-fold faster H 2 recovery and response, respectively, than a pure Pd−Pd gas sensor device. Moreover, the Pd−Ag nanocomposite exhibited a high sensitivity of 5.5% (better than that of other fabricated gas sensors) for 1.6% H 2 concentration. Therefore, we believe that the fabricated nanocomposites appear promising for wide applications in wearable gas sensors, flexible optical devices, and flexible catalytic devices.

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