Nanocellulose/N, P dual-doped graphene composites coupled with aqueous and a sodium alginate-based electrolyte for supercapacitors application

In this paper, innovative solutions are proposed to solve the problem of gravimetric/volumetric performance imbalance in graphene-based electrodes, as well as the technical challenges faced by existing gel electrolytes, such as poor water retention, low ion transport efficiency, and limited temperature adaptability. Herein, Nanocellulose/N, P dual-doped graphene composites (NNPGs) were successfully prepared by the hydrothermal process with graphene oxide (GO), nanocellulose (NC), and triammonium phosphate as precursors. In addition, using sodium alginate (SA), GO, NC, and KOH as starting materials, a new gel electrolyte material (SGNK) with renewable capacity, broad operating temperature range, and excellent water retaining ability was successfully synthesized. Benefiting from the good porous structure, excellent pseudocapacitive properties, and high bulk density of NNPGs, the aqueous symmetric supercapacitor based on NNPG20 exhibits high gravimetric and volumetric specific capacitance (288.2 F g⁻¹, 409.2 F cm⁻³), good rate capability, and favorable cycle stability. More importantly, the flexible solid-state supercapacitors (FSSCs) fabricated with SGNK and NNPGs deliver high specific capacitance (216.8 F g⁻¹), benign renewable performance, excellent bending resistance, and a wide operating temperature range. In summary, the SGNK and NNPGs developed in this work have important reference value for the design of advanced energy storage devices.