A new MoCN monolayer containing stable cyano structural units as a high-efficiency catalyst for the hydrogen evolution reaction

In the hydrogen evolution reaction (HER), it is essential to find a high-efficiency and nonprecious electrocatalyst comparable to Pt, which needs to have rich inherently active sites and good conductivity. By combining a global minimum structure search and first-principles calculations, a hitherto unknown 2D MoCN monolayer was found, which can be considered as a structure in which Mo atoms interact with the stable CN units through triple bonds. The resultant MoCN monolayer possesses superior thermodynamic, dynamic, thermal, and mechanical stabilities, as well as inherent metallicity. In particular, it can exhibit outstanding HER catalytic activity due to the presence of many active sites with near-zero ΔG_H* values, whose density totals 1.80 × 10¹⁵ sites per cm², even more than Pt. In addition, we also propose a series of other 2D monolayers containing stable CN units (i.e., MoC₂N, MoCN₂ and MoC₂N₂), all of which can uniformly show high stability and good HER catalytic activity. Applying strain can further effectively improve the activities of C-rich (MoC₂N) and N-rich (MoCN₂) monolayers, inducing considerably high HER catalytic performance. For the MoCN, MoC₂N and MoCN₂ monolayers, the most active sites are located at the Mo-C-N chain involved. All these fascinating findings can not only provide new excellent candidates but also new insights into the design of highly efficient and nonprecious HER electrocatalysts as an alternative to Pt in the near future.