Stretchable Unsymmetrical Piezoelectric BaTiO₃ Composite Hydrogel for Triboelectric Nanogenerators and Multimodal Sensors

Improving output performance of triboelectric nanogenerators (TENGs) is crucial for expanding their applications in smart devices, especially for flexible and wearable bioelectronics. In this study, we design and fabricate a flexible, stretchable, and highly transparent TENG based on an unsymmetrical PAM/BTO composite film, made of polyacrylamide (PAM) hydrogel and BaTiO₃ nanocubes (BTO NCs, BTO), and the TENG performance can be tailored by adjusting the amount and distribution location of BTO. The stretchable hydrogel electrode could bear over 8 times stretching. By changing the content and distribution location of BTO in the unsymmetrical hydrogel film, the output of the fabricated TENGs could be improved, acting as pressure sensors with high sensitivity to distinguish a spectrum of forces (0.25–6 N) at the low frequency. The mechanism of the enhanced output performance of the PAM/BTO composite hydrogel-based TENG is discussed in detail. By integrating piezoresistive, piezoelectric, and triboelectric effects, the optimized TENG and piezoresistive sensors are used as multimodal biomechanical sensors for detecting the motions of human bodies, pressure, and curvature with high sensitivity.