Oxygen and Nitrogen Co‐enriched Sustainable Porous Carbon Hollow Microspheres from Sodium Lignosulfonate for Supercapacitors with High Volumetric Energy Densities

Abstract

Abstract Oxygen and nitrogen co‐enriched hierarchical porous carbon hollow microspheres are synthesized by using biomass‐derivative sodium lignosulfonate as a feedstock through a facile and scalable process. This four‐step synthesis process involves spray drying, thermal stabilization, carbonization, and post nitric acid modification. The as‐obtained carbon exhibits a moderate but efficient porosity (specific surface area of 991 m 2 g −1 , total pore volume of 0.75 cm 3 g −1 ), small particle size of 0.2–5 μm, high electrode density of 0.45 g cm −3 , and abundant surface oxygen/nitrogen species (13.12 at.%/0.97 at.%). Its electrochemical performance is evaluated by assembling into supercapacitors in 7 M KOH electrolyte. The three‐electrode cell presents a high gravimetric capacitance of 284 F g −1 at 0.1 A g −1 and good rate capability of 43.6 % at 20 A g −1 . While the two‐electrode cell gives an impressive volumetric capacitance of 21.2 F cm −3 at 0.1 A g −1 , marvelous volumetric energy density of 2.9 Wh L −1 at 11.3 W L −1 , and remarkable cycling stability of 93.4 % capacitance retention after 10000 cycles, which is superior or comparable to that of commercial activated carbon.