The electrochemical performance of supercapacitors using porous carbon as electrodes is strongly affected by the fabrication process of carbon material. KOH is commonly used as an activator combined with urea as a nitrogen dopant. However, the roles of KOH and urea in pore structure configuration and the electrochemical behavior of porous carbon electrodes are still ambiguous. Herein, the optimum porous carbon is obtained when KOH and urea are used simultaneously. KOH is used as a pore-forming substance, whereas urea is employed as a nitrogen source for the nitrogen doping of porous carbon, which increases its defect sites while reducing the graphitization degree. More importantly, urea also expands pores as a pore-enlarging agent, inducing interconnected porous structures. As a result, a hierarchical porous structure is formed and ascribed to the synergistic effect of KOH and urea, and the specific surface area reached 3282 m² g⁻¹ for sample PC800-4. The specific capacitance is 319 F g⁻¹ at 0.5 A g⁻¹ with excellent cycling stability over 2500 cycles. Furthermore, the symmetric supercapacitor reaches an excellent energy density of 11.6 W h kg⁻¹ under 70.0 W kg⁻¹ in a 6 M KOH electrolyte. Our work contributes to the rational designation of the porous carbon structure for supercapacitor applications.

Triple‐doped (P, S and N) peanut‐shell carbon (PSN‐PSC) was fabricated by a flexible one‐step strategy. The obtained carbon displayed large specific surface area and multiple porous structures, hence it was suitable in applying on supercapacitor as electrode materials. Steam explosion was performed to pretreat peanut shells for the purpose of preliminarily creating pore structure. Potassium phosphate was used as activating agent and supplied phosphorus atom. Thiourea was added as pore‐generating agent, as well as nitrogen and sulfur sources. The extremely high specific surface area (2046 m² g⁻¹) and hierarchical porous structure of the PSN‐PSC increased the accessibility of the carbon surface to the electrolyte, which shortened the ion diffusion pathway. Besides, the heteroatoms (P, S, N) doping improved the ability of energy storage and capacitive property. The synergistic effect of heteroatom doping and hierarchical structure endowed PSN‐PSC with the highest specific capacitance of 334.7 F g⁻¹ at 0.1 A g⁻¹ and with remarkable cycle stability of 96 % retention for 10000 cycles in 6 m KOH electrolyte in a three‐electrode system with a 3.0 mg cm⁻² mass loading of PSN‐PSC. Furthermore, the PSN‐PSC symmetric supercapacitor reached an excellent energy density of 19.92 Wh kg⁻¹ under 70 W kg⁻¹ in a 6 m KOH electrolyte. This work demonstrates a novel, convenient method for fabricating heteroatom doped carbon electrode materials, especially based on pretreated biomass wastes.