Water induced ultrathin Mo2C nanosheets with high-density grain boundaries for enhanced hydrogen evolution

Probing the direct effect of grain boundaries as active catalytic sites is very challenging. Here, the authors reveal that the d(z)(2) orbital energy level of Mo atoms in grain boundaries exhibits an intrinsic relationship with the hydrogen evolution activity. Grain boundary controlling is an effective approach for manipulating the electronic structure of electrocatalysts to improve their hydrogen evolution reaction performance. However, probing the direct effect of grain boundaries as highly active catalytic hot spots is very challenging. Herein, we demonstrate a general water-assisted carbothermal reaction strategy for the construction of ultrathin Mo2C nanosheets with high-density grain boundaries supported on N-doped graphene. The polycrystalline Mo2C nanosheets are connected with N-doped graphene through Mo-C bonds, which affords an ultra-high density of active sites, giving excellent hydrogen evolution activity and superior electrocatalytic stability. Theoretical calculations reveal that the d(z)(2) orbital energy level of Mo atoms is controlled by the MoC3 pyramid configuration, which plays a vital role in governing the hydrogen evolution activity. The d(z)(2) orbital energy level of metal atoms exhibits an intrinsic relationship with the catalyst activity and is regarded as a descriptor for predicting the hydrogen evolution activity.

Automated summary

Probing the direct effect of grain boundaries as active catalytic sites is challenging, but the d(z)(2) orbital energy level of Mo atoms shows an intrinsic relationship with the hydrogen evolution activity. Controlling grain boundaries is an effective way to improve the hydrogen evolution reaction performance of electrocatalysts. The construction of ultrathin Mo2C nanosheets with high-density grain boundaries on N-doped graphene through water-assisted carbothermal reaction strategy provides a higher density of active sites, resulting in excellent hydrogen evolution activity and superior electrocatalytic stability.