Flexible Two-Dimensional Ti3C2 MXene Films as Thermo-Acoustic Devices.

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