Hydrogen evolution on different facets of δ1- MoN and δ3-MoN: Considering the adsorbed oxygen and hydroxyl by Surface Pourbaix diagrams

delta(1)-and delta(3)-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. 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. It is interesting that several delta(1)-and delta(3)-MoN surfaces demonstrate comparable exchange current density, e.g., (101) and (001)N of delta(1)-MoN, and (110) of delta(3)-MoN with 1.76, 1.97 and 0.17 mA cm(-2), respectively. This work is expected to contribute to the theoretical understanding of HER on different delta(1)-and delta(3)-MoN surfaces, and provide guidance for corresponding experiments on them. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

The delta(1)-and delta(3)-MoN phases show potential applications in hydrogen evolution due to their excellent corrosion resistance and high conductivity. However, there is still a lack of theoretical studies on hydrogen evolution reactions on their different surfaces. Detailed atomic structure studies reveal that *O and *OH can change catalytic sites and weaken hydrogen adsorption abilities, providing important guidance for experiments and applications.