Conductive, self-healing and adhesive cellulose nanofibers-based hydrogels as wearable strain sensors and supercapacitors

Conductive hydrogels show high potential for application in different areas including wearable electronic devices, human-computer interaction, electronic skin, and intelligent robots. Herein, a simple one-pot method was used to develop a conductive hydrogel by mixing cellulose nanofibers (CNF), polyvinyl alcohol (PVA)-borax and sodium chloride (NaCl) doped poly(3,4-ethylenedioxythiophene):poly (styrene sulfonate) (PEDOT:PSS). The CNF was introduced into PVA-borax gel system, obtaining a hydrogel with improved mechanical, self-healing, and adhesion properties via dynamic boron-ester bonding and multiple hydrogen bond crosslinking. The as- assembled strain sensor was highly sensitive (GF=3), when stretching quickly, it had a fast response time (170 ms) and wide strain sensing range (0-300 %). Moreover, the sensor accurately monitored joint movement and weak muscle throbbing in real time when attached to human skin. Furthermore, supercapacitors were assembled with hydrogel and carbon cloth electrodes, the hydrogel-based supercapacitor has an area specific capacitance of 23.57 mF/cm2 with a high cycle life of > 5000 cycles. This study offers guidance for constructing cellulose-based conductive hydrogel systems and promotes their application in flexible sensors and supercapacitors.