Theoretical predication of the high hydrogen evolution catalytic activity for the cubic and tetragonal SnP systems

By means of density functional theory (DFT) calculations, we have systematically investigated the structures and hydrogen evolution reaction (HER) catalytic activities for the cubic and tetragonal SnP systems, both of which can be viewed as the stacking of SnP layers possessing structural features similar to the famous phosphorene. It is revealed that the (111) and (200) facets are the possible exposed surfaces of the cubic structure, while the possible exposed surfaces of the tetragonal structure are (101), (10), (110), (002) and (00) facets. The computed surface energies reveal that the P-terminated (111) surface and the (200) surface of the cubic SnP system as well as the P-terminated (101) and (10) surfaces and the (110) surface of the tetragonal SnP system can be considered as the more stable surfaces, in view of more favorable surface energy. The computed free energy values of H* (ΔGH*) show that all these stable surfaces can possess considerably high HER catalytic activity over a wide range of hydrogen coverage. It is found that the top sites over P atoms can serve as the most active sites on these surfaces, and the tetragonal structure can even exhibit a higher HER activity than the cubic structure. Moreover, the correlative catalytic mechanisms have been analyzed in detail. Coupled with the metallic conductivity, two kinds of bulk SnP systems can be very promising candidates as a high-performance and low-cost HER electrocatalyst. All these fascinating findings can be beneficial for promoting the application of excellent SnP-based materials in catalyzing the water splitting process.