Preparation of manganese/nitrogen-sulfur carbon electrodes from black liquor of bamboo pulp for supercapacitors

Biomass-derived porous carbons from low-cost lignin are the promising candidate electrode for aqueous supercapacitors. Notably, the poor charge storage ability severely hinders the industrial production. The sodium lignosulphonate was firstly prepared by methylsulfonation with formaldehyde (HCHO) and sodium sulfite (Na2SO3). Then, lignin-based N-S co-doped porous carbon materials (LNSC) were prepared via one-step carbonization with sodium lignosulphonate as raw material and urea as a nitrogen source dopant and mild activator. And, MnCO3 nanowires were prepared and loaded on LNSC to fabricate manganese/nitrogen-sulfur carbon composites (LNSC/Mn-x) with high electrochemical performance. The prepared LNSC/Mn-40 was dominated by micro-mesopores with a total pore volume of 1.01 cm3 g-1 and a specific surface area of up to 770.68 m2 g-1. In a three-electrode system, LNSC/Mn-40 showed a specific capacitance of 234.92 F g-1 at 0.5 A g-1 in 6 M KOH electrolyte, greatly better than LNSC (151.98 F g-1 at 0.5 A g-1), while the symmetric supercapacitor demonstrated a maximum energy density of 7.21 Wh kg-1 at a power density of 5765 W kg-1 along with good cycling stability of 69.77% capacitance retention for up to 10000 cycles. The results suggested that lignin can be considered as an ideal candidate for porous carbon electrode for supercapacitors and reduce industrial production cost.