A comparative study of physically activated biochars with multiple aqueous binders for sustainable supercapacitors

Abstract

Electric double-layer capacitors were fabricated using CO 2 -activated carbons derived from three biochar precursors, two industrial Finnish biochars and an in-house willow biochar, combined with water-based chitosan and styrene-butadiene rubber/carboxymethyl cellulose binders. The study examines how precursor-dependent pore development and binder formulation affect device performance in neutral aqueous NaCl. Under identical activation conditions, A-G-BC combined the highest activation yield, 64%, with the highest BET surface area, 918 m 2 /g, and total pore volume, 0.750 cm 3 /g. HS-2D-NLDFT analysis showed that A-G-BC contained a substantially larger mesopore volume of 0.446 cm3/g, whereas A-C-BC and A-W-BC exhibited similar micropore volumes and micropore fractions. Symmetric two-electrode devices operated from 0 to 1.2 V showed predominantly electric double-layer behaviour. A-G-BC with SBR/CMC delivered 23.9 F/g at 5 mV/s and retained 14.1 F/g at 100 mV/s, while also exhibiting the lowest ESR and leakage current. However, A-C-BC with SBR/CMC produced a slightly higher low-rate GCD capacitance, showing that BET area alone did not determine charge storage. Selected devices retained 96 to 97% of their capacitance after 10,000 cycles, and A-G-BC with SBR/CMC retained 93.65% after the segmented 90 h voltage-hold ageing test. The results show that precursor dependent pore texture and electrode formulation jointly influence resistance, rate response and stability in water processed biochar based supercapacitors. FESEM, Raman spectroscopy and XPS further identified precursor dependent differences in morphology, carbon structure and surface chemistry following activation, while post exposure FESEM provided a qualitative comparison of formulation dependent electrode morphology.