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Polyimide-based nitrogen-doped ordered mesoporous carbon was successfully synthesised utilising SBA-15 as a hard template. By controlling the molar ratio of 4,4′-oxydianiline to pyromellitic dianhydride during copolymerising and carbonisation, nitrogen-doped ordered mesoporous carbon (NOMCx) with various nitrogen content and pore distribution were obtained. When the molar ratio of 4,4′-oxydianiline to pyromellitic dianhydride was 6, NOMC6 presented the highest content of nitrogen (7.94 wt%) and moderate specific surface area (890 m2 g−1). Accordingly, NOMC6 showed a high specific capacitance of 282 F g−1 at 0.1 A g−1, and excellent cycle stability (no capacitance loss over 10,000 cycles) in 1 M H2SO4. The synthesised ordered mesoporous carbons do not show a significant decrease of capacitive performance in the current density range of 2 to 20 A g−1. Furthermore, a symmetrical supercapacitor consisting of two NOMC6 electrodes exhibited an energy density of 4.77 Wh kg−1 at power density of 500 W kg−1 (1 A g−1).

To meet the demand for high-power-density and long lifespan surpercapacitors (SCs), the Ni–P@Ni HL/CC-1h with a core–shell structure (Ni–P sphere as the core and nanoflake with the Ni and Ni–P heterogeneous layer as shell) was constructed via a facile strategy. The strategy included hydrothermal synthesis of Ni–P spheres with large Ni surface layer on carbon cloth (Ni–P@Ni HL/CC) and subsequent chemical dealloying using HCl as etching solution in order to remove the redundant Ni substances. The morphology, composition, and electrochemical performances of raw Ni–P@Ni HL/CC and the corresponding samples obtained by different dealloying times (0.5, 1, and 2 h) were characterized. Interestingly, the Ni–P@Ni HL/CC-1h presents a unique structure with a nanoflake shell and a porous core, which can provide a large number of exposed active sites, accelerate electrolyte ion diffusion and support ultra-long cycling. Furthermore, the Ni species existing in the outer flake can increase the conductivity and promote the capacitance during the charge–discharge processes. The Ni–P@Ni HL/CC-1h exhibited high specific capacity of 280.8 C g−1 at current density of 1 mA cm−2, high rate retention of 76.2% at 20 mA cm−2. The maximum specific capacity could reach 388.8 C g−1 at 8 mA cm−2, and maintained the 92.6% retention after 3000 cycles. Moreover, the Ni–P@Ni HL/CC-1h//AC all-solid-state asymmetric supercapacitor (ASC) exhibited high specific capacity, 86.0% retention after 10,000 cycles and high energy density of 27.6 Wh kg−1 at power density of 942.8 W kg−1.