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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 PCM (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 specific 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. Image 1 • Ternary B, N, P-doped carbon material was obtained via polymer dehalogenation. • High B loading of 11.5 at.% was achieved, which is key to suppress water splitting. • Thanks to heavy heterodoping, pseudocapacitance of BNP-C was much enhanced. • BNP-C rendered high capacitance of 518 F g−1 and maintained ∼260 F g−1 at 100 A g−1. • BNP-C achieved large workable voltage of 1.5 V and high energy of 12.0 Wh kg−1. [ABSTRACT FROM AUTHOR]