A flexible Zn-ion capacitor based on wood derived porous carbon and polyacrylamide/cellulose nanofiber hydrogel

To achieve the sustainable development of portable electronic device, there arises an urgent need for exploiting the safe and wearable energy storage device from natural resources. Herein, a flexible Zn-ion hybrid capacitor (ZIHC) is developed using the oil palm wood derived hierarchical porous carbon (PC) and cellulose nanofiber (CNF)-based hydrogel as cathode and electrolyte, respectively. The PC is synthesized via the KOH-assisted carbonization approach, which exhibits high surface area of 1210.05 m2·g-1 and hierarchical porous structure that can offer abundant active sites to accumulate electrolyte ions and accelerate the diffusion of electrolyte ions. Through in-situ polymerization and impregnation strategies, the polyacrylamide/cellulose nanofiber (PAM/CNF) hydrogel electrolyte with high ionic conductivity (17.7 mS·cm-1) is successfully produced. Consequently, a flexible ZIHC based on the as-prepared PC and PAM/CNF hydrogel electrolyte delivers a favorable specific capacity of 67.4 mAh·g-1 at 0.2 A·g-1, a large energy density of 53.7 Wh·kg-1 at 152.9 W·kg-1, and remarkable cycling stability. Furthermore, the ZIHC possesses a stable capacitive behavior in different bending states. This work provides guidance for the sustainable development of portable energy storage device from the abundant, renewable, inexpensive woody biomass.