Nanostructural design of biomass-derived porous carbons for advanced supercapacitors

: Almond shell, a representative lignocellulosic biomass, is employed as a precursor to fabricate porous carbons with tunable local graphitic nanocrystalline domains and hierarchical porosity via H 2 SO 4 pretreatment followed by H 3 PO 4 activation and high-temperature pyrolysis. Comprehensive structural analyses reveal 6 M H 2 SO 4 pretreatment leads to lignin enrichment and promotes locally ordered graphitic domains, while constructing a mesopore-dominated network with a specific surface area of 1180 m 2 g -1 and mesopore fraction of 97.7%. In contrast, excessive acid pretreatment at 12 M shifts the pore structure toward smaller pores and introduces more oxygen-containing groups. In 6 M KOH aqueous electrolyte, a symmetric supercapacitor based on the best performing material AC6-600(1000) delivers high specific capacitance of 152.9 F g -1 at 1 A g -1 , retaining 83.2% of that capacitance at 20 A g -1 . It also maintains 81.1% of its initial capacitance after 100000 cycles at 10 A g -1 . A flexible, free-standing, high-mass-loading electrode (∼14.3 mg cm -2 ) fabricated from AC6-600(1000) achieves areal capacitance of 1715.2 mF cm -2 , areal energy density of 228.7 μWh cm -2 , further confirm the excellent rate capability of AC6-600(1000). Density functional theory (DFT) calculations show locally ordered carbon surfaces exhibit stronger adsorption toward K + ions, establishing a correlation between nanocrystalline order and interfacial charge storage. This work proposes a “nanocrystalline–pore co-design” strategy for biomass-derived carbons into advanced device performance in supercapacitors.