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.