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

Abstract

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 H2SO4 and NaOH, and a solid-phase physical separation using CHCl3-H2O, 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 m2 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 TEABF4/ACN electrolytes at 1 A g−1. The extracted Cr in the form of Cr2O3 was used to produce high-voltage cathode material, LiMnCrO4. 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.