Black liquor-derived porous carbons from rice straw for high-performance supercapacitors

Abstract

Rice straw is pretreated with KOH aqueous solution and the resulting liquid is used to synthesize a black liquor-derived porous carbon (BLPC) in which KOH acts as both lignin extraction solvent and chemical activation agent. The addition of melamine into the black liquor leads to an increase in the surface area (2646m2g−1), pore volume (1.285cm3g−1) and promotes the formation of nitrogen covalent bonds in the carbon materials (N-BLPC). Melamine used as additive has dual roles as nitrogen source and pore modifier of the carbon material. The as-prepared materials have specific capacitances of 242Fg−1 (BLPC) and 337Fg−1 (N-BLPC) when used as electrodes in 6M KOH electrolyte at a current density of 0.5Ag−1. The assembled N-BLPC-based symmetric supercapacitor shows stable cycling (>98% retention after 3000 cycles at 10Ag−1). The proposed strategy offers a facile method to produce porous carbons from waste black liquor in biorefinery or pulp and paper processes.