Transparent, conductive cellulose hydrogel for flexible sensor and triboelectric nanogenerator at subzero temperature.

Herein, flexible, transparent and conductive cellulose hydrogels were directly fabricated by regenerating the chemically cross-linked cellulose in NaCl aqueous solution, without further treatment. NaCl played a dominant role on the mechanical, optical, conductive and anti-freezing properties of cellulose hydrogel, also endowed the hydrogel with safety. After optimization, the transparency, tensile strength, elongation at break and conductivity of the cellulose hydrogel reached 94 % at 550 nm, 5.2 MPa, 235 %, and 4.03 S/m, respectively, as well as low temperature tolerance down to -33.5 ℃. Furthermore, sensors based on cellulose hydrogel demonstrated fast response and stable sensitivity to tensile strain, compressive pressure, and temperature, at both room and subzero temperature, without obvious hysteresis. The cellulose hydrogel based triboelectric nanogenerator demonstrated stability and durability as energy harvester in harsh conditions. In addition, the established approach can be used to prepare flexible, transparent and conductive cellulose hydrogel with various salts, indicating universality, simplicity and sustainability for the fabrication of cellulose based flexible conductive devices.