Interfacial Electric State Reconstruction of CuS Nanosheets via Indium-Doping for Electro-Removal of Heavy Metal Anions

Electro-reductive removal of heavy metal anions holds great potential for clean production. However, its application is hindered by a low removal efficiency and high energy consumption, due to inefficient electron and mass transfer under strong electrostatic repulsion and the occurrence of undesirable side reactions. In this study, we doped atomic In into the CuS nanoparticles to modify the built-in electric state of the CuS lattice, thus enhancing the reduction and removal of Cr2O72– (Cr(VI)). The In-doped CuS electrode (0.08In-CuS) achieves a 100% reduction efficiency for Cr(VI) within 20 min, with a Faradaic efficiency of 97.42%, and completely removes total Cr within 100 min, with kinetic constants five times higher than those of CuS. Detailed characterization and theoretical simulations revealed that the introduction of atomic In results in the deformation of the triangularly coordinated and tetrahedrally coordinated Cu layers and the displacement of atoms in the CuS lattice. The electron-deficient state of In resulted in a polarization of the electron distribution of Cu, thus promoting strong adsorption of both Cr(VI) and Cr(III). This work highlights the necessity of modulating the intrinsic electric field of the electrode surface in order to achieve the effective removal of heavy metal anions.