Objective Although biochar is widely used in energy and environmental electrode materials, its performance is often limited by bottlenecks such as insufficient specific surface area, unbalanced pore structure, and limited electrochemical activity. To overcome these limitations and achieve high-value utilization of agricultural waste, this study used bulk solid waste Sasangua cake (SC) as a precursor, aiming to prepare biochar electrode materials with high specific surface area, hierarchical pore structure, and high specific capacitance.

Method The study adopted the “pre-carbonization-KOH activation” preparation route to investigate the effects of activation temperature (600 and 750℃) on the material’s structure and performance. The ash content was measured using the standard combustion method to analyze material purity; N₂ adsorption-desorption was used to characterize structural parameters such as specific surface area, pore size distribution, and pore volume; cyclic voltammetry, galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) were employed to comprehensively evaluate the material’s specific capacitance, rate performance, and ion transport in 1 mol/L H₂SO₄和3 mol/L KOH electrolytes.

Result (1) The specific surface areas of SC-600 and SC-750 reach as high as 1 642.0 and 1 649.1 m²/g, respectively, exhibiting a hierarchical micro-, meso- and macroporous structure. The carbon content of SC-750 (82.17%) is significantly higher than that of SC-600 (64.09%), while its ash content decreases to 3.7% and the I_ᴅ/I_ɢ slightly increases to 1.089, indicating that high-temperature activation purifies the carbon skeleton while introducing more defects. (2) EIS fitting reveals that in H₂SO₄, the charge-transfer resistance (R_ct) of SC-600 (0.11 Ω) is much lower than that of SC-750 (0.36 Ω), whereas in KOH, the R_ct of SC-750 (0.19 Ω) is significantly lower than that of SC-600 (1.00 Ω), revealing the differentiated requirements of different electrolyte ions for the defect structure of the material. (3) The capacitance of the Sasangua cake-derived biochar material is dominated by electric double-layer capacitance. At 5 mV/s in H₂SO₄, the specific capacitance of SC-600 is 379.7 F/g, higher than that of SC-750 (278.3 F/g); however, at a current density of 0.5 A/g in H₂SO₄, the GCD specific capacitance of SC-750 reaches as high as 590 F/g, demonstrating excellent low-current capacity. (4) In KOH electrolyte, when the scan rate increases from 5 mV/s to 100 mV/s, the capacitance retention of SC-750 is 77.1%, significantly superior to the 69.2% of SC-600, indicating that an increase in mesopore proportion is beneficial for improving the rate performance.

Conclusion Through temperature regulation, a high-performance SC-based hierarchical porous biochar electrode material was successfully prepared, addressing the challenges of synergistic optimization of specific surface area and pore structure, as well as poor rate capability in traditional biomass-derived carbon materials. The positive role of high activation temperature in enhancing structural integrity and electrochemical kinetics was revealed.