First-Principles Studies On The Hydrogen Evolution Reaction Activity Of MoN Surface

Hydrogen energy as an ideal clean energy has attracted wide attention.A highly efficient catalyst has been explored to replace precious platinum for hydrogen production:δ1-andδ3-MoN,the two most stable phases of molybdenum nitride,show a potential application in hydrogen evolution as their excellent corrosion resistance and high conductivity.However,we still lack the theoretical study about HER on their different surfaces.In order to simulate the realistic condition during heterogeneous catalysis,detailed atomic structure of each MoN surface（the*O and*OH）is determined by surface Pourbaix diagram.Then,the effect of different adsorption sites and coverage on hydrogen evolution activity was systematically studied and the exchange current density of the surface also was calculated.Finally,by analyzing the density of states of surface atoms as adsorption sites,we also explore the relationship between the band centers and the free energy of H adsorption（ΔG_H）.This work is expected to contribute to the theoretical understanding of HER on differentδ1-andδ3-MoN surfaces and provide guidance for corresponding experiments on them.Our specific research results are as following:（1）.Mo and N atoms on the MoN surface are the active sites for hydrogen evolution reaction in the aqueous environment.（2）.It is interesting that severalδ1-andδ3-MoN surfaces demonstrate comparable exchange current density,e.g.,（110）,（101）and（001）N ofδ₁-MoN,and（110）ofδ₃-MoN with 0.17,1.76,1.97 and 0.17 m A cm^-2,respectively.（3）.Further exploration of hydrogen evolution shows that the*O and*OH could change the catalytic site of one MoN surface,and weak the hydrogen adsorption ability.This is attributed to the downshift of Mo d-band center in top layer caused by the*O and*OH.And the hydrogen adsorption ability on catalytic sites of N and O atoms also follow the p-band center theory,respectively.