Computational studies on structural and electronic properties of NiCo₂S₄ (001)/KOH electrolyte interface

In this work, we present a study on the atomic details and the electronic structure of the NiCo₂S₄/KOH electrolyte interface via first-principles calculation. Both Ni-terminated and CoS₂-terminated NiCo₂S₄ (001) surfaces are studied in order to understand the electronic structure of the interface and surface reactivity. The surface free energy indicates that the Ni-capped NiCo₂S₄ (001) surface is more stable than the CoS₂-capped one. Upon adsorption, KOH received more electrons (0.1e) from the latter surface than from the former and the planar average differential charge density indicates that a larger electric dipole forms in CoS₂-terminated NiCo₂S₄/KOH interface. These analyses prove that the CoS₂-terminated NiCo₂S₄ (001) surface presents a stronger affinity for OH⁻ in the electrolyte, which leads to the enhanced electrochemical performance. These results will not only contribute to a better understanding of the fundamental knowledge of the NiCo₂S₄/KOH electrolyte interface, but also provide a guidance as to enhance the electrochemical activity of NiCo₂S₄ materials, which will benefit the ultimate application of NiCo₂S₄ (001) as electrode material for electrochemical energy storage.