Efficient utilization of lignin residue for activated carbon in supercapacitor applications

Lignin is an organic polymer that is a key structural material in most plant support tissues. However, only 2% of lignin produced worldwide is commercially utilized; while the remainder is burned as fuel. It has been proven that a high carbon content and extensively bridged polymer structure are useful in creating high-value products. Herein, larch and the lignin obtained using the Klason and organosolv methods were converted into activated carbon samples for use as supercapacitors. This lignin showed higher values in carbonization yield. All other activated samples exhibited similar physical and electrochemical properties, pore structures, and surface areas. Transmission electron microscopy revealed that all samples had partially graphitic structures, which provide electron pathways and energy storage capabilities. Lignin-derived activated carbon shows the highest gravimetric specific capacitance (131 F g−1, at 1 mA cm−2), specific capacitance retention ratios of cycling stability (99% at 10 mA cm−2 for 10,000 cycles), and rate capability (91% at 30 mA cm−2). These results suggest high yield, good cycling stability, high capacitance, and eco-friendly material for supercapacitor electrodes.