Hypercoordinated Si/Ge driving excellent HER catalytic performance in new TM2X (X = Si and Ge) monolayers: a high-throughput investigation by screening transition metal elements

Abstract

Designing nonprecious and highly efficient HER electrocatalysts is a challenging but crucial task. Through first-principles structure search calculations, we have identified two-dimensional (2D) Co₂Si and Co₂Ge materials containing planar hypercoordinated Si/Ge. Further, based on these two fascinating structures, a series of additional TM₂X (X = Si and Ge) monolayers with the hypercoordinated Si/Ge are also obtained by screening 3d, 4d, and 5d transition metal atoms. Almost all of these 2D monolayers can exhibit high thermodynamic, dynamical, thermal, and mechanical stabilities, as well as inherent metallicity. Among them, a total of nine monolayers, including planar, quasi-planar, or buckled TM₂Si (TM = Co, Fe, Pd, and Pt) and TM₂Ge (TM = Co, Ni, Fe, Pd, and Ir) systems, can uniformly present high HER catalytic activity. Particularly, the Co₂Si, Co₂Ge, and Ni₂Ge monolayers containing the planar hypercoordinated Si/Ge can exhibit considerably high HER catalytic activity over a wide range of θ_H* coverages (even up to 3ML). Their active site density can reach as high as 3.471 × 10¹⁵ to 4.341 × 10¹⁵ site per cm², surpassing many reported materials and even Pt. A related analysis of the catalytic mechanism has been conducted. These remarkable findings can be beneficial for the future realization of excellent HER catalysts.