Upcycling chrome-tanned leather waste into electrode materials for supercapacitors and high-voltage Li-ion batteries

Conventional disposal methods of chromium-tanned leather waste (CTLW) pose significant environmental pollution and potential leaching of heavy metals into soil and water. To address this issue, we designed a sustainable recycling method to convert CTLW into value-added products through chromium extraction and activated carbon production. Three different approaches, including two solution-phase extractions using H 2 SO 4 and NaOH, and a solid-phase physical separation using CHCl 3 -H 2 O, were introduced to remove Cr from the chemically activated biochar. The physicochemical analysis shows no trace of Cr in the final carbon sample, which is highly microporous and has a specific surface area of 1934 m 2 g −1 . The activated carbon was then used in a symmetric supercapacitor and tested in organic and aqueous electrolytes. The cell exhibits a maximum specific capacitance of 181.4 F g −1 in 6 M KOH, and 112.8 F g −1 in 1 M TEABF 4 /ACN electrolytes at 1 A g −1 . The extracted Cr in the form of Cr 2 O 3 was used to produce high-voltage cathode material, LiMnCrO 4 . The prepared Li-half cell shows a high specific capacity of 192.7 mAh g −1 along with notable stability and coulombic efficiency. This dual-functional approach mitigates environmental hazards and promotes sustainable resource utilization for energy storage applications. • A novel solid-phase physical separation method is developed for removing Cr from tanned leather waste. • Physicochemical analysis shows 99% of Cr extracted from the activated carbon after the acidic, basic and physical separation. • Cr 2 O 3 derived from leather waste is used for the synthesis of high-voltage cathode material LiMnCrO 4 . • The recovered activated carbon as a symmetric supercapacitor electrode shows excellent performance in aqueous electrolyte.