Shrub waste spins supercapacitor gold for zinc-ion storage

A discarded ornamental shrub could soon power electric buses. Researchers at Northwest A&F University report that Aucuba japonica, normally chipped for mulch, becomes a high-performance cathode when heated for minutes under microwave irradiation with phosphoric acid and steam. The combined activation enlarges micropores from 0.54 nm to 0.71–1.13 nm—exactly the dimensions needed to host the 0.86 nm hydrated zinc ions that ferry charge in zinc-ion hybrid supercapacitors (ZiHSCs). The resulting carbon, labeled PHAC, shows 1 490 m² g⁻¹ surface area and 58 % mesopore volume; its oxygen-rich surface lowers charge-transfer resistance to 12.97 Ω. In coin-cell testing the PHAC cathode delivers 269 mAh g⁻¹ at 0.2 A g⁻¹ and retains 64 % capacity when the current is pushed to 100 A g⁻¹. When paired with a zinc-foil anode, the full device provides 210 Wh kg⁻¹ at 1.3 kW kg⁻¹—tripling the energy density of earlier biomass-carbon devices—and survives 20 000 cycles with only 6 % fade. In situ X-ray diffraction reveals that sulfate-assisted Zn₄SO₄(OH)₆·5H₂O crystallites form reversibly on the carbon surface, storing charge without lattice swelling that degrades graphite. Molecular dynamics simulations confirm that the enlarged slit pores reduce desolvation energy from +0.12 eV to –0.94 eV, accelerating ion transport and suppressing dendrites. Techno-economic assessment indicates PHAC can be produced for roughly one-third the cost of coconut-shell carbon, suggesting a scalable route to cobalt- and lithium-free storage for grid and automotive applications.

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DOI

https://doi.org/10.1016/j.jobab.2025.08.002

Original Source URL

https://www.sciencedirect.com/science/article/pii/S236996982500057X

Journal

Journal of Bioresources and Bioproducts