Metalloid-doping in SMoSe Janus layers: first-principles study on efficient catalysts for the hydrogen evolution reaction

B, Si, and Ge dopants are inserted into SMoSe Janus layers (JLs) at Mo, S, and Se as well as at interstitial sites. Spin-polarized density functional theory calculations are employed to investigate the modified structural and electronic properties of the layers, the energetics of dopant incorporation, and the effect of doping on the interaction of the two-dimensional material with hydrogen. The detailed structural analysis exposes the influence of dopant atomic sizes on lattice distortion. The formation energy E-f of dopant X (X = B, Si, and Ge) at substitutional and interstitial sites is studied for two different chemical environments: (i) bulk X - or X-rich conditions, and (ii) dimer X-2 - or X-poor conditions. It is found that under X-poor conditions, the stability of the dopants is always higher. Doping at the S site is energetically most favored, with E-f(B) < E-f(Si) < E-f(Ge). The electron redistribution in the JLs due to the presence of dopants is explored using Bader analysis. Atomic sites with a number of electrons different from that on atoms in pristine SMoSe JLs may be potential hydrogen traps and are therefore interesting for the hydrogen evolution reaction (HER). Consequently, the interaction of H atoms with these sites is studied and the H adsorption energy is calculated. While pristine SMoSe JLs repel H, several attractive sites are found in the vicinity of the dopant atoms. In order to quantify the feasibility of the doped SMoSe JLs for use as a catalyst for the HER, the free adsorption energy is determined. The data show that all dopants may improve SMoSe for HER applications. The most favorable sites are B at S and Se, Si at Mo and S, and Ge at Mo and S. In particular, adsorption and desorption of H on B-doped (at S and Se sites) and on Ge-doped (at an Mo site) JLs may be rapid. The present results demonstrate the potential of metalloid-doped SMoSe JLs as efficient HER catalysts.