Porous carbon materials (PCMs) have been extensively investigated as electrode materials for supercapacitors, yet are severely hindered by low capacitance and energy density. Herein, we reported the efficient synthesis of a ternary B, N, P-doped PCMs (termed as BNP-C) via polymer dehalogenation strategy. The atomic contents of B, N, and P, as characterized by XPS, are 11.5, 1.1, and 0.8 %, respectively, yet intriguingly resulting in limited water splitting activity due to the overwhelmingly presented B dopant. This specific feature can be taken advantage of for effectively expanding the workable voltage window while maintaining large capacitances of aqueous supercapacitors (ASCs). Besides, the BNP-C exhibited porous 3D structure, hierarchical porous structure, and large surface area of 1118.5 m2 g-1, which simultaneously ensured the BNP-C-assembled ASC with superior capacitive performance. As confirmed by both Dunn and Trasatti methods, pseudocapacitance remarkably contributed ~44.9 and ~40.2 % respectively in overall capacitances for the BNP-C, which was mainly credited to the heavy decoration of B. In addition, the BNP-C symmetric ASC delivered very good long-term stability and high specific energy of 12.0 and 10.9 Wh kg-1 in acidic and alkaline electrolytes, respectively.