Skin‐Inspired and Self‐Powered Piezoionic Sensors for Smart Wearable Applications

Bio-inspired by tactile function of human skin, piezoionic skin sensors recognize strain and stress through converting mechanical stimulus into electrical signals based on ion transfer. However, ion transfer inside sensors is significantly restricted by the lack of hierarchical structure of electrode materials, and then impedes practical application. Here, a durable nanocomposite electrode is developed based on carbon nanotubes and graphene, and integrated into piezoionic sensors for smart wearable applications, such as facial expression and exercise posture recognitions. The nanocomposite electrode provides abundant channels for ion transfer because of its hierarchically porous structure. Carbon nanotubes not only prevent restacking of graphene nanolayers, but also connect them across out-plane dimension. The piezoionic skin sensors present a high degree of linearity in a wide strain range with high sensitivity, and long cycling life with bending strains beyond 20 000 s. Further, a smart bracelet based on flexible sensors is fabricated for accurate posture recognition of badminton exercise, valuable to athlete training.