Treatment and utilization of chromium-tanned leather waste for energy materials as an alternative approach to current energy technologies: a review

The textile and footwear industries generate over 1.2 million tons of chromium-tanned leather waste annually, posing severe environmental and health risks due to the presence of toxic Cr(III) and Cr(VI) compounds. This review critically evaluates current treatment technologies and valorization strategies for repurposing this waste into high-performance energy materials. Although leather waste contains up to 50 to 60% organic content and 3 to 5% chromium, its potential as a carbon-rich precursor remains underexplored. This review is the first to comprehensively address its application in energy systems, with a focus on electrochemical performance, specific surface area (ranging from 300 to 1200 m 2 /g in modified carbonized materials), and environmental impact mitigation. Promising approaches include hybridization with carbonized biomass, metal oxides, and conductive polymers, resulting in materials suitable for supercapacitors, batteries, fuel, and solar cells. Life-cycle assessment (LCA) studies show up to 30% reduction in environmental footprint compared to conventional synthetic materials. Despite these advances, challenges remain in scaling laboratory successes to industrial production. The review concludes that while significant strides have been made, further research is needed to optimize material properties, improve process economics, and fully integrate LCA into development pipelines to support sustainable, large-scale implementation of leather waste-derived energy materials.