Structural Modulation through Se Vacancies on Zn-Doped NiSe₂ Nanoparticles for Expediting Electrocatalytic Hydrogen Evolution

Several distinctive approaches have been continuously explored in order to promote the electrocatalytic efficacy of transition metal chalcogenides. Herein, we envisioned to trigger the electrocatalytic HER activity of a chalcogenide, i.e., NiSe₂, through zinc doping and subsequent creation of selenium vacancies (V_Se) on the Zn-doped NiSe₂. Zn-doping on an electrocatalyst could judiciously tune its electronic structure, and subsequent creation of V_Se would afford active sites for hydrogen adsorption, thus facilitating the overall electrochemical HER process. Zn-doped NiSe₂ nanoparticles (Zn_xNi_1–xSe₂ NPs) with different amounts of Zn (as dopant) were synthesized, among which Zn_0.4Ni_0.6Se₂ NPs exhibited maximum electrocatalytic HER activity. Thereafter, Zn_0.4Ni_0.6Se₂ NPs were calcined at 400 °C for different time periods to induce different amounts of V_Se. Interestingly, Zn_0.4Ni_0.6Se₂ NPs calcined for 2 h (V_Se-Zn_0.4Ni_0.6Se₂-2H NPs) demonstrated a superior electrochemical HER performance compared to all the synthesized catalytic materials with a lesser overpotential and Tafel slope of 123 mV at 10 mA cm^–2 and 37.1 mV dec^–1. Theoretical calculations using the first-principles method were well in accordance with the experimental observations, wherein the V_Se-Zn_xNi_1–xSe₂ NPs as electrocatalysts portrayed the lowest hydrogen adsorption free energy in the energy profile. Additionally, V_Se-Zn_0.4Ni_0.6Se₂-2H NPs sustained excellent stability for 12 h in 0.5 M H₂SO₄.