Publication date: 15th December 2025
Biomass-derived porous carbons are attractive electrode materials for sustainable supercapacitors [1], yet the rational coupling of local graphitic order with hierarchical porosity remains challenging [2]. Herein, almond shell, a representative lignocellulosic biomass, is employed as a precursor to construct a series of porous carbons with tunable local graphitic nanocrystalline domains and hierarchical structures. By combining H₂SO₄ pretreatment at different concentrations (0, 6, and 12 M) with H₃PO₄ activation and two-step thermal treatment, porous carbons denoted as AC0-600(1000), AC6-600(1000), and AC12-600(1000) are obtained. Comprehensive FTIR, SEM, HRTEM, XRD, Raman, N₂ adsorption–desorption isotherms, and XPS analyses reveal that 6 M H₂SO₄ pretreatment enriches lignin and promotes the formation of locally ordered graphitic domains, while simultaneously constructing a mesopore-dominated pore network with a specific surface area of 1180 m² g⁻¹ and a mesopore fraction of 97.7%. In contrast, 12 M pretreatment introduces excessive micropores and oxygen-containing functional groups, which has shown to be detrimental. In 6 M KOH aqueous electrolyte, a symmetric supercapacitor based on AC6-600(1000) delivers a high specific capacitance of 152.9 F g⁻¹ at 1 A g⁻¹, retains 83.2% of its capacitance at 20 A g⁻¹, and maintains 91.5% and 81.1% of its initial capacitance after 20000 cycles at 5 A g⁻¹ and 100000 cycles at 10 A g⁻¹, respectively. A flexible, free-standing, high-mass-loading electrode (~14.3 mg cm⁻²) fabricated from AC6-600(1000) achieves an areal capacitance of 1715.2 mF cm⁻², a maximum areal energy density of 228.7 µWh cm⁻², and a volumetric energy density of 3.1 mWh cm⁻³, while retaining 86.1% of its capacitance after 3000 cycles. Pouch-type symmetric devices further confirm the excellent rate capability. Density functional theory (DFT) calculations show that locally ordered carbon surfaces exhibit stronger adsorption toward K+ ions, thereby establishing a clear correlation between nanocrystalline order and interfacial charge storage. This work proposes a “nanocrystalline–pore co-design” strategy that provides a structural design framework for effectively translating the intrinsic properties of biomass-derived carbons into high device-level performance in supercapacitors.
The authors would like to acknowledge the financial support provided by Ministerio de Ciencia y Innovacion (MCIIN), the Agencia Estatal de Investigacion (AEI) and the European Regional Development Fund (FEDER) (grants PID2024-157199OB-C21) and the Severo Ochoa Centres of Excellence programme, Grant CEX2021–001214-S, for this research activities. L.P. Wang also acknowledges his scholarship (No. 202206420015) under China Scholarship Council.
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