H3PO4-Assisted Synthesis of Apricot Shell Lignin-Based Activated Carbon for Capacitors: Understanding the Pore Structure/Electrochemical Performance Relationship

The main focus of this study was to give an idea for the value added from lignin and further understand the pore structure/electrochemical performance relationship. A case study of using H3PO4-assisted apricot shell lignin (ASL) was used to synthesize apricot shell lignin-based activated carbon (AAC) for capacitors. Considering performance and cost, the activation temperature of ASL was 550 °C. The as-obtained AAC-3 possesses the highest specific surface area (1474.82 m2/g) and the highest mass-specific capacitance (169.05 F/g) upon the current density of 0.5 A/g. Compared with the correlation coefficient (R2) of specific surface area and mass-specific capacitance, the R2 of V0.85–1.93 nm and mass-specific capacitance was higher. Therefore, when employing a three-electrode configuration with a 6 M KOH electrolyte, the V0.85–1.93 nm can be used as a universal predictor of mass-specific capacitance at a low current density ranging from 0.50 to 10.00 A/g. Additionally, such a range of characterized pore size (0.85–1.93 nm) exhibited 2.83–6.43 times the diameters of K+ and OH–.