Atmosphere-free activation methodology for holey graphene/cellulose nanofiber-based film electrode with highly efficient capacitance performance

An efficient chamber-induced activation method was applied for the preparation of holey graphene/cellulose nanofiber-based film with high specific surface area (SSA) and multiple channels through the graphene nanosheets. With the cellulose nanofiber (CNF) simultaneously serving as “dispersing agent,” “spacer,” and “activating agent,” the graphene oxide (GO) nanosheets are perforated by the pyrolysis gas from CNF in the confined space inside the hybrid films, uniformly dispersed, and sandwiched between CNF networks with less agglomeration and restacking. Additionally, we have proved that H₂O and H₂ are primarily responsible for the activation and etching of GO/CNF film. As the CNF content increases, the mesoporosity of the activated reduced GO/CNF (A-RGO/CNF) film increases, and the graphene nanosheets show more nanopore perforations. Benefitting from the high SSA, high density, moderate mesoporosity, and abundant channels for ion diffusion through the graphene nanosheets, the A-RGO/CNF film exhibits the highest specific capacitance of 323 (236) F g⁻¹ (F cm⁻³) at 1 A g⁻¹. For the A-RGO₅/CNF₅ film containing half CNF and half GO, an excellent comprehensive electrochemical performance including superior rate performance (208 (160) F g⁻¹ (F cm⁻³) at 60 A g⁻¹) is exhibited. Moreover, the A-RGO₅/CNF₅ electrode in an all-solid-state flexible symmetric supercapacitor delivers a high specific capacitance of 250 (193) F g⁻¹ (F cm⁻³) at 1 A g⁻¹. This study provides a novel idea for the preparation of holey graphene-based film for supercapacitor electrodes. The strategy of simultaneously employing CNF as “dispersing agent,” “spacer,” and “activating agent” also offers a new vision for the assembly of homogeneous nanohybrid material and the utilization of pyrolysis gas.