Facile synthesis of B/N co-doped 2D porous carbon nanosheets derived from ammonium humate for supercapacitor electrodes

Abstract

In this work, we report a facile method for preparing the B/N co-doped 2D porous carbon nanosheets (BNHCs) with high contents of boron (3.41–3.96 at.%) and nitrogen (5.1–6.09 at.%) via annealing the mixtures of ammonium humate and H3BO3. The ammonium humate is used as nitrogen-containing carbon precursor, and H3BO3 acts as boron source and pore-forming agent. Moreover, we demonstrate firstly that the existence of H3BO3 can enhance the graphitization degree of BNHCs by inducing the conversion of BCO2 to BC3 with increasing the H3BO3/ammonium humate mass ratio to 2. BNHC-1.5 exhibits the highest specific surface area of 592 m2 g−1 among all the samples, and BNHC-2 shows the enhanced graphitization degree and highest mesopore ratio (60.5%). In a three-electrode system, the BNHC-1, BNHC-1.5 and BNHC-2 exhibit high specific capacitances of 305 F g−1, 311 F g−1 and 225 F g−1 at 0.2 A g−1, and 64 F g−1, 125 F g−1 and 120 F g−1 at ultrahigh current density of 100 A g−1, respectively. Moreover, as assembled symmetric supercapacitor electrodes with high active material mass loading (∼180 μm, ∼13 mg cm−2), BNHCs deliver high specific capacitances of 170–210 F g−1 at 0.05 A g−1, and BNHC-2 presents an outstanding cyclic stability (94.8% capacitance retention after 10,000 cycles), making them promising candidates for practical supercapacitor application.