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A flexible piezoelectric composite is composed of a polymer matrix and piezoelectric ceramic fillers to achieve good mechanical flexibility and processability. The overall piezoelectric performance of a composite is largely determined by the piezoelectric filler inside. Thus, different dispersion methods and additives that can promote the dispersion of piezoelectric ceramics and optimal composite structures have been actively investigated. However, relatively few attempts have been made to develop a filler that can effectively contribute to the performance enhancement of piezoelectric devices. In the present work, we introduce the fabrication and performance of the composite piezoelectric devices composed of Li-doped ZnO nanowires (Li: ZnO NWs) grown on the surface of MXene (Ti 3 C 2 ) via the hydrothermal process. Through this approach, a semiconductor−metal hybrid structure is formed, increasing the overall permittivity. Moreover, the Ti 3 C 2 layer can serve as a local ground in the composite so that the ferroelectric phase-transformed Li: ZnO NWs grown on its surface can be more effectively polarized during the poling process. In addition, the NW-covered surface of Ti 3 C 2 prevents the aggregation of metallic Ti 3 C 2 particles, promoting a more uniform electric field distribution during the poling process. As a result, the output performance of the piezoelectric nanogenerator (PENG) fabricated with a Li: ZnO NW/Ti 3 C 2 composite was greatly improved compared to that of the devices fabricated with Li: ZnO NWs without the Ti 3 C 2 platform. Specifically, the Li: ZnO NW/Ti 3 C 2 composite piezoelectric nanogenerator (PENG) demonstrated a twofold higher output power density (∼9 μW/cm 2 ) compared with the values obtained from the PENG devices based on Li: ZnO NWs. The approach introduced in this work can be easily adopted for an effective ferroelectric filler design to improve the output performance of the piezoelectric composite. KEYWORDS: piezoelectric nanogenerator (PENG), zinc oxide (ZnO) nanowires on MXene (Ti 3 C 2 ), hydrothermal growth, composite, phase transition

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Fe 3 O 4 nanoparticles dispersed on single-walled carbon nanotube (SWCNT) composites are synthesized through a simple in-situ co-arc discharge process followed by an annealing process. A well-integrated Fe 3 O 4 /SWCNT composite exhibiting the strong microwave absorption (MA, À36.9 dB at 10.5 GHz) and a wide effective bandwidth (5.5 GHz) is obtained by controlling the annealing conditions. The high effective MA performance of this composite was ascribed to the well integration of magnetic nanoparticles (Fe 3 O 4 ) on the SWCNT, creating a synergetic effect. This work demonstrates an economical approach to produce Fe 3 O 4 /SWCNT composites with good MA performance.