High-performance and flexible sodium ion-based electrochemical devices toward self-powered wearable volatile organic compounds sensing system

Abstract

Self-powered wearable electronic systems are considered the ideal solution to realize ubiquitous Internet-of-Things (IoT), personalized healthcare, and point-to-care diagnosis. Here, we demonstrate the integration of a high-performance and ultra-stable sodium ion-based micro-supercapacitor (MSC) and a high-sensitive sensor for self-powered wearable Volatile Organic Compounds (VOC) sensing systems. It is found that a sodium-based solid electrolyte exhibited high ionic conductivity, reaching 2.4 mS cm−1 at 70 °C. Further, the inclusion of TiO2 NPs additive in the solid electrolyte can reduce the crystallinity and expand the electrode/electrolyte interface, which increases about 2.25 times in the capacitance of sodium ion-based MSC. PDMS-encapsulated MSC showed ultra-stability of capacitance retention (approximately 98.8 %) after 50,000 cycles while also achieving a high flexibility of 1000 cycles with a minimal capacitance change. As a proof-of-concept of a self-powered wearable sensor, it is demonstrated that an integrated polymer electrolyte-based VOC sensor powered by a charged-MSC can continuously operate for more than 4000 s (over 1.1 h) in the ethanol/nitrogen gas chamber. Therefore, we believe that our integration of sodium ion-based electrochemical storage and VOC sensor capabilities will pave a way to revolutionize the approach of wearable electronic applications toward self-powered systems.