Aqueous ZIHCs combine the high energy density of batteries with the high power density and long service life of supercapacitors. Their nonflammable aqueous electrolytes also offer safety and environmental advantages. However, conventional activated-carbon cathodes are dominated by micropores that restrict the movement of hydrated zinc ions and provide insufficient active sites, limiting energy density and cycling durability. Nitrogen doping can improve ion transport, wettability and charge storage, but conventional nitrogen sources, including cyanides and amines, can be costly and environmentally harmful. Sustainable alternatives are therefore needed to produce better-performing cathodes from abundant waste resources.
A study (DOI: 10.48130/scm-0026-0010) published in Sustainable Carbon Materials on 10 March 2026 by Xuesong Zhang's team, China Agricultural University, reports that co-processing biomass and PU waste produces a porous, nitrogen-functionalized cathode with high capacitance, energy density and cycling stability.
The researchers first mixed biomass with PU at different mass ratios and carbonized the mixtures at 800 °C under argon. The resulting carbon precursors were then activated with potassium hydroxide (KOH), creating nitrogen-doped hierarchical porous carbons (NHPCs). Dealkalized lignin was initially used as a model biomass, while reed, corn stover and pine sawdust were subsequently examined to test the method's adaptability. The team varied both the PU-to-biomass ratio and the KOH-to-carbon ratio to identify the best preparation conditions. Scanning electron microscopy, X-ray diffraction, Raman spectroscopy, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy and nitrogen adsorption–desorption measurements were used to characterize morphology, chemical composition, defects, functional groups and pore structure. Electrochemical behavior was evaluated through cyclic voltammetry, galvanostatic charge–discharge testing and electrochemical impedance spectroscopy. The cathodes were first assessed in a three-electrode system and then assembled with zinc-foil anodes and zinc sulfate aqueous electrolyte in coin-cell ZIHCs. Moderate KOH activation generated interconnected micro-, meso- and macropores, whereas excessive activation damaged pore walls and conductive pathways. The optimized material, N-3@AC-4, was obtained using a biomass-to-PU mass ratio of 3:1 and a KOH-to-carbon-precursor ratio of 4:1. It featured a three-dimensional interconnected porous structure with a surface area exceeding 1,100 m² g⁻¹. Nitrogen-containing surface groups improved electrolyte wettability and supplied additional electrochemically active sites, while the hierarchical pores shortened ion-diffusion distances. In the three-electrode system, N-3@AC-4 achieved a specific capacitance of 430.6 F g⁻¹ at 0.1 A g⁻¹. When incorporated into a ZIHC, it maintained 356.9 F g⁻¹ at the same current density and delivered an energy density of 126.89 Wh kg⁻¹ at a power density of 80 W kg⁻¹. The device also preserved approximately 85% of its capacitance after 5,000 cycles at 5 A g⁻¹, with coulombic efficiency close to 100%.
Overall, the study demonstrates that two widespread waste streams—biomass residues and discarded PU—can be co-upcycled into functional carbon cathodes for aqueous ZIHCs. The method replaces conventional nitrogen reagents with PU as an integrated nitrogen source while creating a pore structure suited to zinc-ion transport and storage. Further optimization of pore architecture and heteroatom doping could increase practical energy density and advance scalable cathodes for grid-level renewable-energy storage.
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References
DOI
10.48130/scm-0026-0010
Original Source URL
https://doi.org/10.48130/scm-0026-0010
Funding information
This work was supported by National Natural Science Foundation of China (52206290), the Disciplinary Breakthrough Project of Ministry of Education (MOE, #00975101), and the earmarked fund for CARS (Grant No. 36).
About Sustainable Carbon Materials
Sustainable Carbon Materials (e-ISSN 3070-3557) is a multidisciplinary platform for communicating advances in fundamental and applied research on carbon-based materials. It is dedicated to serving as an innovative, efficient and professional platform for researchers in the field of carbon materials around the world to deliver findings from this rapidly expanding field of science. It is a peer-reviewed, open-access journal that publishes review, original research, invited review, rapid report, perspective, commentary and correspondence papers.