Upcycling electroplating sludge metals into ultrathin NiFeAl-LDH nanosheets for advanced energy storage applications

Abstract

Recovering heavy metals from industrial solid waste and upgrading them into high-value products is of great significance for addressing environmental pollution and promoting resource recycling. In this study, electroplating sludge containing mainly Ni, Fe, and Al was used as the raw material, and by adding nickel chloride to regulate the M(II)/M(III) ratio, the Ni, Fe, and Al in the sludge were converted into high-value NiFeAl-LDH nanosheets with excellent electrochemical properties. At a current density of 1 A g⁻¹, NiFeAl-LDH-2 exhibits a specific capacitance of 1763.4 F g⁻¹. When assembled as the cathode with activated carbon as the anode in a hybrid supercapacitor (HSC), the highest energy density reaches 43.89 Wh kg⁻¹ at a power density of 800 W kg⁻¹. Furthermore, the HSC demonstrates minor capacity decay over 10,000 cycles at a high current load of 4 A g⁻¹, and after connecting two HSC devices in series, the LED indicator light can easily be illuminated. The solid-state NiFeAl-LDH-2//AC hybrid supercapacitor demonstrates potential application in portable electronic devices due to its excellent electrochemical properties, making it feasible to upgrade electroplating sludge into battery electrode materials.