<p>A range of N-doped porous carbon nanostructures (NPCNSs) with different mesoporous morphologies were synthesized through hydrothermal method by using the cationic surfactant 1-hexadecyl-3-methyl imidazole bromine salt (CMMB) as a soft template. By adjusting the ratio of water/ethanol and the amount of cationic surfactants, the controlled morphologic structure (particle size and morphology of carbon nanospheres) is easily achieved. The synthesized N-doped carbon nanostructures are characterized by adjustable particle size, specific surface area, pore capacity, and high proportion of doped heteroatoms N and O. In the 6 M KOH electrolyte, the representative NPCNSs-1.2-10 as the capacitor electrode has excellent electrochemical capacitance (184.68 F g⁻¹ at 0.2 A g⁻¹), high capacitance retention (102 F g⁻¹ at 20 A g⁻¹), and excellent cycling stability (capacitance retention 90.36% at 10 A g⁻¹ after 5000 cycles).</p> Graphical abstract <p></p>