Monolayer triphosphates MP₃ (M = Sn, Ge) with excellent basal catalytic activity for hydrogen evolution reaction

Atomically thin two-dimensional (2D) materials have received intense research interest due to their novel properties and promising applications in nanodevices. By using density functional theory (DFT) calculations, we investigate catalytic activities of several newly predicted two-dimensional (2D) triphosphides GeP₃, SnP₃ and InP₃ monolayers for hydrogen evolution reaction (HER). The calculation results show that GeP₃ and SnP₃ monolayers are active catalysts for HER with suitable free energy of hydrogen adsorption in the basal plane. In particular, the Gibbs free energy of hydrogen adsorption (ΔG_H*) of GeP₃ is 0.024 eV, a value even more favorable compared to the precious-group-metal (PGM) catalyst Pt. Moreover, the 2D GeP₃ and SnP₃ are intrinsically compatible with the graphene substrate so that the HER performance can be improved via building a hybrid multilayer with graphene sheet. The charge transfer from GeP₃ or SnP₃ to graphene, estimated to be 0.1278e or 0.2157e, can significantly enhance the electric conductivity and promote the electrocatalytic activity. Although the electronic band structure of GeP₃ and SnP₃ can be tuned by external strain, we find that the HER performance of GeP₃ and SnP₃ monolayer is actually insensitive to the external strain, a feature desirable for the catalytic application. The desirable properties for HER with nearly zero Gibbs free energy render 2D GeP₃ and SnP₃ promising candidates for future application in electrocatalysis.