Hierarchical porous biochar from Eastern spruce as a supercapacitor electrode material

This study focuses on the production of activated biochar from Eastern spruce (Picea orientalis), a coniferous biomass, for use as an electrode material in supercapacitors. Biochar obtained at 900 °C was chemically activated with KOH at 800 °C using biochar/KOH mass ratios of 1:2, 1:3, and 1:4. The activation process produced porous carbons with a hierarchical pore structure and enlarged surface areas ranging from 555.8 to 1295 m2 g−1. The biochar activated with a 1:4 KOH ratio (ES8K4) exhibited the best electrochemical performance, delivering a specific capacitance of 206 F g−1 at 0.1 A g−1 in a three-electrode configuration. Its superior performance is attributed to a more accessible pore architecture with a lower micropore volume fraction, broader pore size distribution, improved graphitization, and oxygen-containing surface groups that enhanced wettability and electrolyte accessibility. The electrode retained 93.3% of its initial capacitance after 10,000 cycles at 5 A g−1. In a symmetric two-electrode configuration, ES8K4 delivered a specific capacitance of 47 F g−1 at 0.5 A g−1, along with maximum energy and power densities of 6.3 Wh kg−1 and 4374 W kg−1, respectively. The symmetric device also retained 89.1% of its initial capacitance after 10,000 cycles at 5 A g−1. These findings demonstrate that Eastern spruce-derived activated biochar is a promising sustainable electrode material for supercapacitor applications.