Toluidine Blue Functionalized Macadamia Shell Derived Porous Carbon for Enhanced Supercapacitor Performance

This study proposes a synergistic strategy to prepare composite electrode materials by combining porous carbon derived (MNSC) from waste macadamia nut shell (MNS) with redox-active toluidine blue (TB), which effectively suppresses the TB “shuttle effect” and significantly enhances pseudocapacitive energy storage and device energy density. MNSC was synthesized via pre-carbonization and KOH activation, and the optimal MNS-1 exhibited a specific surface area of 1979.38 m²·g⁻¹ and a specific capacitance of 247.57 F·g⁻¹ in 1 M H 2 SO 4 at 1 A·g⁻¹. TB was loaded onto the MNS skeleton via electrostatic self-assembly to form TB-x@MNS-x composites, which were characterized by SEM, XRD, FT-IR, XPS, Raman, and BET. The optimized TB-300@MNS-1 achieved a specific capacitance of 412.9 F·g⁻¹ at 1 A·g⁻¹, with a pseudocapacitive contribution of 80.5% at 1 mV·s⁻¹ and rapid charge transfer. The symmetric supercapacitor assembled with TB-300@MNS-1 electrodes delivered an energy density of 34.81 Wh·kg⁻¹ at 400 W·kg⁻¹, retaining 76.8% capacitance after 10,000 cycles. This work provides a feasible, low-cost design strategy for enhancing the energy density of carbon-based supercapacitors through organic molecule functionalization.