Effect of CNF ratio and pressure on structural and electrochemical performance of hybrid hydrogel for flexible free-standing electrode and sensors.

A 2D flexible hydrogel (GO/CNF) with layered structure and superhydrophilic is synthesized via cross-linking and self-assembling of graphene oxide (GO) with cellulose nanofiber (CNF) through microwave-assisted hydrothermal. CNF acts as "dispersant" and "spacer", making GO nanosheets uniformly disperse on their surface with less agglomerations. The carboxyl groups and hydrophilicity of CNF effectively improve the charge storage capacity of carbon materials through interactions. When the mass ratio of GO to CNF is 3:1, the GO/CNF exhibits an excellent comprehensive electrochemical performance as free-standing electrodes, with the specific capacitance reaching 295 F/g at 0.5 A/g in three-electrode system. The influence of press pressure on GO/CNF reveals that increasing the pressure improves the hydrophilicity of the electrode, favoring their wettability to aqueous electrolyte. GO/CNF-6 possesses the highest degree of graphitization, and delivers a highest mass specific capacitance up to 493 F/g at 0.5 A/g. Flexible solid-state symmetric supercapacitor with GO/CNF-6 as electrodes exhibits an energy density of 20.6 Wh/kg at a power density of 250 W/kg. The good flexibility and biocompatibility of the devices show sensitive current response to biological signals, endowing them potential application prospect in wearable portable electronics and human motion detections.