Facile synthesis of nitrogen-doped carbon materials with hierarchical porous structures for high-performance supercapacitors in both acidic and alkaline electrolytes

Abstract

In this report, we show that a facile and highly adaptable route based on the Schiff-base formation reaction can generate crosslinked polymer precursors for the fabrication of hierarchical porous nitrogen-doped carbon materials. The optimized sample with a moderate surface wettability, Brunauer–Emmett–Teller (BET) surface area, and heteroatom content displays outstanding supercapacitance performances in both acidic and alkaline electrolytes. Capacitances of 362 F g⁻¹ in 1 M H₂SO₄ and 374.5 F g⁻¹ in 6 M KOH at 0.5 A g⁻¹ as well as an excellent rate capability (75% and 79.5% capacitance retention at 30 A g⁻¹ in 1 M H₂SO₄ and 6 M KOH, respectively) are achieved, which are much better than those of the sample fabricated via a conventional synthetic route (acetic acid as the catalyst). Moreover, according to the differing slopes of the discharge portion, the overall specific capacitance is divided into electric double layer capacitor (EDLC) and faradaic capacitance, and EDLC and faradaic capacitance contributions to the overall specific capacitance are analyzed. It is found that the faradaic capacitance is mainly associated with the heteroatom content and the utilization of available heteroatoms. The EDLC capacitance is related to the BET surface area, surface wettability, and the concentration and ionic size of the electrolyte. This simple synthetic strategy may be of interest in the design of crosslinked polymer precursors, thus enabling the fabrication of carbon materials with unique electrochemical properties. Moreover, our finding on EDLC and faradaic capacitance contributions to the overall specific capacitance is crucial for the future fabrication of nitrogen-doped carbons for supercapacitors.