An environment-friendly method to prepare fulvic acid-based porous carbon for high energy density supercapacitors

Abstract

Low energy density (E_g) of supercapacitors (SCs) severely limits their industrial applications. Enhancing the voltage window of SCs is an effective method to achieve a square-fold increase in E_g. 3D hierarchical porous carbons (FPs) with high yield (14.5 %) and high conductivity (87 S m⁻¹) were prepared by an interfacial self-assembly method using low-cost biomass fulvic acid (FA) as a carbon resource and employs P123 as a structure-directing agent. The soft template P123 establishes a key role in the formation of FPs. It not only enhances the pore connectivity of FPs but also induces an interfacial orientation of the carbon micro-domains in FA. Furthermore, high-temperature annealing can repair the carbon network of FPs, thus FPs are endowed with high electrical conductivity, low carbon defects and low oxygen content (4.1 at.%), which leads to superior voltage-withstanding properties. By exploiting its structural advantages, the optimized sample FP800 exhibits a specific surface area of 1938 m² g⁻¹, sp² carbon (88.5 %), a high mesopore ratio of 30.76 % and a high voltage of 3.2 V in commercial TEABF₄/PC electrolyte. It gets high C_g of 107 F g⁻¹ at 1 A g⁻¹, high rate performance (C_10/0.05) of 82.0 % and maximum E_g of 39.1 Wh kg⁻¹. Furthermore, it also obtains an ultra-stable lifespan with 90.6 % capacity retention after 60,000 cycles. Compared to FP750 and FP850, FP800 has a more reasonable electrochemical performance.