Stretchable, self-healing, adhesive and anti-freezing ionic conductive cellulose-based hydrogels for flexible supercapacitors and sensors

Conductive hydrogels have great application potential in flexible electronic devices. Nevertheless, it is a huge challenge to fabricate multifunctional conductive hydrogels simultaneously integrated with high conductivity, self-healing performance, adhesiveness and anti-freezing ability. Herein, multifunctional ionic conductive hydrogels composed of sodium carboxymethyl cellulose, polyacrylic acid and NaCl are designed via a facile one-pot polymerization method based on the tannic acid-ferric ions autocatalytic system. The multifunctional hydrogel shows high stretchability (1170%, 104 kPa), an elastic modulus of 0.088 MPa, a toughness of 0.680 MJ m-3 and adhesiveness (wood: 22.95 +/- 2.59 kPa). Metal coordination and H-bonding endow the hydrogel with good self-healing (98.3% for strain recovery), and NaCl is responsible for high ionic conductivity (2.818 S m-1) and anti-freezing performance (conductivity of 1.738 S m-1 at - 25 degrees C). The multifunctional hydrogel is assembled into a flexible supercapacitor with a high specific capacitance of 144.94 F g-1, long-term stability (15,000 cycles) and low-temperature tolerance (- 27.5 degrees C). A flexible strain sensor based on the multifunctional hydrogel has a gauge factor of 6.77 (750-1050%) and is applied for monitoring human motions. The multifunctional hydrogel also can serve as a flexible bioelectrode to detect electromyographic and electrocardiographic signals, even working at low temperature (- 7 degrees C).