Lithium stabilizes square-two-dimensional metal sheets: a computational exploration

Abstract

Based on the M₄-square-containing M₄Li₂ (M = Al, Ga, In, Tl, Ge, Sn, Pb, Sb, Bi, Cu, Ag, Au, and Hg) clusters, we computationally designed two-dimensional (2D) M₂Li sheets consisting of M₄-square motifs. The four M₂Li-I (M = Sb, Bi, Ag, and Au) monolayers with Li square sublayer sandwiched between two M square sublayers (P4/mmm space group) were confirmed to be stable (high cohesive energies, positive vibrational frequencies, moderate Young's moduli, and structural integrity during first-principles molecular dynamics simulations at 500 K), and the particle swarm optimization (PSO) method identified these constructed monolayers as the global minima in the 2D space. The three M₂Li-I (M = Sb, Bi, and Ag) monolayers demonstrated a half-auxetic behavior. Ag₂Li-I could well activate CO₂ and convert it into HCOOH by following the path * → *CO₂ → *OCHO → *HCOOH → *+HCOOH. Particularly, Ag₂Li-I shows great promise as an electrocatalyst for CO₂ reduction as its limiting potential is as low as 0.40 (0.27) V without (with) considering the solvent effect. Our theoretical explorations reveal that lithium can stabilize the square metal monolayers, and the stable square binary metal sheets exhibit diverse mechanical and electrochemical properties, which can be used in the fields of mechanics and electrochemical catalysis.