Oxygen- and Nitrogen-Enriched Honeycomb-Like Porous Carbon from Laminaria japonica with Excellent Supercapacitor Performance in Aqueous Solution

Oxygen- and nitrogen-enriched honeycomb like porous carbon was synthesized using Laminaria japonica as precursor by ethanol extraction and chemical activation. The resultant materials had a cavity morphology with wall thickness from 0.15 to 0.93 mu m, high specific areas (2000 m(2)/g), a hierarchical micropore-mesopore structure, high oxygen (17.7 wt %), and moderate nitrogen (1.5 wt %) contents. At 1 A/g and 50 A/g, the honeycomb-like porous carbon displayed a prominent capacitance of 381 and 268 F/g in KOH electrolyte (6 mol/L), and 382 and 160 F/g in H2SO4 electrolyte (1 mol/L), respectively. Moreover, in KOH aqueous electrolyte (6 mol/L), the symmetric honeycomb like porous carbon electrode offered a maximum single electrode capacitance (248 F/g, 1 A/g), energy density (8.6 Wh/kg), and high capacitance retention of 91% after 10 000 cycles at 2 A/g. The synergism of developed pore structure with developed micropore structure, honeycomb-like morphology, and oxygen-/nitrogen-enriched chemical groups provided a high ion-accessible surface area and shorter diffusion path for electrolyte ions. High wettability resulted in high specific capacitance, good rate capability, and cycling stability as supercapacitor electrodes.