Nitrogen-Doped Porous Carbon Enabled by a Dual-Functional NH ₄ Cl-Assisted Strategy for Quasi-Solid-State Supercapacitors

The development of high-performance supercapacitor electrode materials critically depends on the concurrent optimization of porosity and heteroatom doping. Herein, a simple NH 4 Cl-assisted dual-functional strategy is proposed to convert inedible sprouted potato starch into nitrogen-doped porous carbon, enabling the simultaneous modulation of pore structure and nitrogen configuration within a single thermal process. Systematic comparisons of different nitrogen sources (melamine, urea, and NH 4 Cl) under identical synthesis conditions reveal that NH 4 Cl exhibits more evident dual-functional roles in the present system, contributing to both pore regulation and nitrogen incorporation. Its presence is proposed to influence the distribution state of Zn-containing species during activation, which may contribute to the formation of a high-surface-area porous structure (1589 m 2 g –1, 97% micropore contribution) favorable for charge storage. Meanwhile, as a nitrogen source, NH 4 Cl effectively introduces graphitic nitrogen (34.98% of total nitrogen, and 2.51 of absolute content), facilitating electron transport and interfacial charge transfer. The resulting NPCT-N electrode delivers a high specific capacitance of 438 F g –1 at 1 A g –1 and maintains 270 F g –1 under a commercial-level mass loading of 10 mg cm –2 . Furthermore, a gel-based quasi-solid-state flexible symmetric supercapacitor assembled with this electrode achieves an energy density of 32 Wh kg –1 at 900 W kg –1, with two devices connected in series providing a stable output voltage of 3.6 V. This NH 4 Cl-assisted approach provides a simple route for converting inedible sprouted potato starch into nitrogen-doped porous carbon for energy storage applications.