Upcycling of Multi-Metal Contaminated Wastewater into High-Entropy Layered Double Hydroxide for Oxygen Evolution Reaction

The rapid growth of the electric vehicle industry has driven up nickel demand for batteries. However, the release of various metals during the smelting of nickel-containing ore leads to complex multi-metal contaminated smelting wastewater. Herein, CaFe layered double hydroxide (denoted as CaFe) is synthesized for the treatment of multi-metal contaminated wastewater, achieving removal efficiencies of 98.0%, 98.6%, 100%, and 100% for Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺, respectively. The quasi-situ X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) results indicate the formation of high-entropy LDH of CaCoNiCuZnFe by the isomorphic substitution of Ca²⁺ in CaFe. Meanwhile, lattice distortion and the formation of metal vacancies can be observed due to the introduction of metals with different ionic radii and the dissolution of Ca²⁺. Given the stability and abundant active sites of high-entropy material, the CaCoNiCuZnFe shows good OER performance with an overpotential of 310.7 mV at 10 mA cm⁻² and long-term stability of 250 h. Density functional theory (DFT) calculations reveal that lattice distortion optimizes intermediate adsorption energy by enhancing M─O covalency and metal vacancy activates lattice oxygen by generating non-bonding oxygen, which synergistically triggers the lattice oxygen mechanism (LOM). This strategy converts multi-metal contaminated wastewater resources into valuable products and achieves dual goals of environmental remediation and resource utilization.