▎ 摘　　要

Acid-stable, non-noble catalysts are promising for hydrogen evolution reaction (HER); however, they get easily damaged when used in acidic electrolytes, thus reducing the HER lifetimes. Moreover, completely blocking catalysts from acidic electrolytes degrades HER performance. To achieve a balance between the HER lifetime and performance, we vary the number of N-doped graphene layers (1-2, 2-3, and 3-5 layers) encapsulating NiMo nanoparticles as efficient HER catalysts and obtain the optimal number of protective layers. Our data show that 3-5 graphene layers achieved the best balance, with a stable current density of 100 mA cm(-2) for 25 h in 0.5 M H2SO4. Density functional theory calculations are performed to show the effect of encapsulating graphene layer number on the catalytic activity and protection of non-noble NiMo in acidic electrolytes.