Non-noble Metal Single Atoms Anchored on Janus Transition Metal Dichalcogenide Monolayers for Hydrogen Evolution Reaction

Combining non-noble metal atoms with a transition metal dichalcogenide (TMD) monolayer is a promising strategy for designing single-atom catalysts (SACs) tailored for the hydrogen evolution reaction (HER). Our extensive first-principles calculations incorporating the implicit solvation model show that single-atom (SA) Cu and Zn anchored on vacancy-defected Janus TMD MXY monolayers (where M = W or Mo; X/Y = S, Se, or Te) exhibit better catalytic activity for the HER. As the electronegativity of the X atoms at the top surface gradually increases relative to that of the Y atoms at the bottom surface, the bond of Cu–M or Zn–M correspondingly strengthens. This effect weakens the adsorption of hydrogen atoms on either Cu or Zn, promotes the formation of SA-Cu and SA-Zn at the vacancy sites, and increases the hydrogen adsorption Gibbs free energy. The application of a 1% biaxial tensile strain to Janus TMD monolayers increases the Cu–M or Zn–M bond strength and simultaneously reduces the formation energies of SA-Cu and SA-Zn. The strong correlation between the electronegativity difference of the top and bottom chalcogen atoms and the catalytic activity of the Cu and Zn atoms highlights a distinct mechanism for designing non-noble metal SACs for the HER by utilizing Janus TMD monolayers and strain engineering.