Hierarchically Porous Carbons from Almond Residues via Hydrothermal Pretreatment and Mild K2CO3 Activation for Aqueous Zinc Hybrid Supercapacitors

Shaj, Densa A. ; Alvira, Darío ; Antorán, Daniel ; Sebastián, Víctor ; Manyà, Joan J. (Universidad de Zaragoza)

Resumen: Agricultural residues offer a scalable feedstock for sustainable carbon electrodes, yet achieving high electrochemical performance in aqueous zinc-ion hybrid supercapacitors (ZHSCs) often relies on harsh activating agents and low carbon yields. Here, almond-tree pruning residues (AT) and almond shells (AS) are converted into porous carbons via hydrothermal pretreatment (HTC) followed by mild K2CO3 activation, enabling hierarchical porosity while limiting excessive burnoff. The HTC-assisted route markedly enhances N2-accessible surface area and mesopore volume, improving electrolyte accessibility and ion-transport pathways, while the presence of oxygen-containing groups contributes to favorable interfacial interactions in aqueous media. AT-derived carbons consistently outperform AS counterparts, highlighting the strong influence of precursor architecture on activation efficiency and pore connectivity. In a two-electrode aqueous ZHSC configuration (Zn metal anode; porous carbon cathode), the best performing AT-derived electrode delivered a specific capacity of 142 mAh g–1 at 0.1 A g–1 with 91% capacity retention after 10,000 cycles at 10 A g–1. Electrolyte chemistry plays a key role in durability: zinc trifluoromethanesulfonate (ZTFS) provides higher capacity retention and improved reversibility than ZnSO4, consistent with a more uniform Zn deposition and the formation of a less crystalline, fluorine-containing interphase, as evidenced by post-mortem analyses. Electrochemical impedance spectroscopy and galvanostatic intermittent titration techniques further support faster interfacial kinetics and more favorable transport in the best-performing carbon, in line with its balanced hierarchical porosity and surface chemistry. The device achieves an energy density of 87.8 Wh kg–1 at 62.3 W kg–1 and retains 37.9 Wh kg–1 at 13.6 kW kg–1, matching or surpassing many biomass-derived ZHSC cathodes prepared using more corrosive chemicals. Overall, this work demonstrates a greener, yield-efficient pathway to high-performance carbon cathodes for aqueous zinc-based hybrid energy storage.

Idioma: Inglés

DOI: 10.1021/acs.energyfuels.6c00654

Año: 2026

Publicado en: Energy and Fuels (2026), [16 pp.]
ISSN: 0887-0624

Financiación: info:eu-repo/grantAgreement/ES/DGA/T22-23R
Financiación: info:eu-repo/grantAgreement/EC/HORIZON EUROPE/101120311/EU/Towards innovative and affordable sodium- and zinc-based electrochemical energy storage systems composed of more sustainable and locally-sourced materials/eNargiZinc

Tipo y forma: Article (Published version)

Área (Departamento): Área Ingeniería Química (Dpto. Ing.Quím.Tecnol.Med.Amb.)