Upcycling distillery waste: N, P, Fe Co-doped porous biochar from excess sludge of sauce-flavor liquor for high-performance supercapacitors

Abstract

Enhancing supercapacitor performance by incorporating heteroatoms into biochar represents a fascinating strategy. Our study presented an uncomplicated process for creating porous biochar simultaneously doped with nitrogen (N), phosphorus (P), and iron (Fe). The source material was excess sludge from sauce-flavor liquor production, which conveniently provided high initial N and Fe content for the resulting biochar. The phosphorus originated from phytic acid, while gentle activation was achieved using potassium carbonate (K₂CO₃). We found that adjusting the K₂CO₃ proportion and activation heating allowed precise control over the final material's characteristics, including its pore network, surface chemistry, plus the ultimate N, P, and Fe levels. Through electrochemical assessment, the N, P, Fe/BC-700-2 sample demonstrated superior performance, exhibiting a specific capacitance up to 141.7 F g⁻¹ when tested at a 1 A g⁻¹ current density in 6 M KOH electrolyte. This efficacy stemmed from several contributing elements: a large specific surface area (BET, 824.5 m² g⁻¹), abundant structural imperfections coupled with extensive mesoporosity, and advantageous synergistic effects arising from N, P, Fe co-incorporation. This investigation demonstrates that transforming sauce-flavor liquor excess sludge (SFLS) into heteroatom-enriched biochar not only offers significant promise for developing advanced supercapacitor electrode materials but also provides a sustainable pathway for valorizing problematic industrial waste.