Unlocking Quantum Catalysis in Topological Trivial Materials: A Case Study of Janus Monolayer MoSMg

Abstract

The emerging field of topological catalysis has received significant attention due to its potential for high-performance catalytic activity in the hydrogen-evolution reaction (HER). While topological materials often possess fragile surface states, trivial topological materials not only offer a larger pool of candidates but also demonstrate robust surface states. As a result, the search for topological catalysts has expanded to include trivial schemes. In this study, a novel 2D Janus monolayer, MoSMg, which demonstrates exceptional obstructed atomic insulating behavior, is presented. Crucially, this trivial metallic topological state exhibits clean obstructed surface states, leading to a significant enhancement in catalytic performance for the HER in electrochemical processes, particularly under high hydrogen coverage. Moreover, the edge sites of this MoSMg monolayer exhibit even more superior catalytic activity, characterized by near-zero Gibbs free energies. In these findings, the way is paved for exploring new avenues in the design of quantum electrocatalysts, especially within the realm of trivial topological materials.

Keywords: Gibbs free energies; hydrogen‐evolution reaction catalysts; obstructed Wannier charge centers; obstructed atomic insulators; obstructed edge states.

Figure 1

a) Top and side views of the Janus monolayer MoSMg, with the unit cell indicated by black dashed lines. b) The 2D Brillouin zone and its projection onto the [010] edge. c) Phonon dispersion calculated for the MoSMg monolayer. Nine phononic bands corresponding three atoms in the unit cell. d) Ab initio molecular dynamics simulation of MoSMg at 300 K using a 5 × 5 × 1 supercell configuration. A slight thermal‐induced structural fluctuation can be seen from the initial and final lattice captures.

Figure 2

a) The electronic band structure of the Janus monolayer MoSMg with the consideration of the spin–orbital coupling effect. Inset illustrates the distribution and location of the OWCCs. b) Edge state for the [010] edge projection with the metallic obstructed edge state. c) Three hydrogen adsorption sites on the MoSMg monolayer and the charge‐transfer visualization at S1 site. d) Calculated ΔG _H* for hydrogen adsorption at different sites.

Figure 3

a,b) Calculated ΔG _H* with H coverage on the MoSMg monolayer for S1 and S3 sites, respectively. c,d) The corresponding atomic structure of hydrogen adsorption on the S1 and S3 sites of the 3 × 3 MoSMg monolayer surface.

Figure 4

a) The hexagonal unit cell of Janus monolayer MoSMg with the lattice constant indicated. b) The transformed orthorhombic unit cell, which is obtained by using the rotation transformation matrix (R) presented. Two different border terminations can be derived, namely, armchair and zigzag. c,d) Zigzag and armchair terminations of the nanoribbons (along with lattice parameters) and their corresponding edge Fermionic accumulations.

Figure 5

a) Calculated ΔG _H* for hydrogen adsorption at two edge sites of the monolayer MoSMg. The two insets illustrate the zigzag and armchair edge sites with the hydrogen stabilized at the Mo positions. b) Volcano plot for ΔG _H* of the two edge sites with that of various pure noble metals, topological Weyl semimetals, and other experimentally synthesized 2D monolayer materials and typical topological catalysts. The data are taken from the literature.^{[ 18} , ²² , ³⁰ , ³¹ , ³² , ⁷⁵ , ⁸⁴ , ⁸⁵ , ⁸⁶ , ^{87 ]} c) The edge DOSs around the Fermi level for the two edge sites. d,e) Plot of the d‐band center (ε _d) and edge DOSs as a function of ΔG _H* for the two edge sites.