Spatially strain‐induced and selective preparation of Mo _<i>x</i> N ( <i>x</i>  = 1, 2) as a highly effective nanoarchitectonic catalyst for hydrogen evolution reaction in a wide pH range

Developing highly efficient catalysts for the hydrogen evolution reaction (HER) is crucial to commercial water splitting in the global efforts to mitigate fossil fuel combustion and combat global climate change. Molybdenum nitrides (Mo x N) such as γ‐Mo 2 N and δ‐MoN are promising HER catalysts. Although δ‐MoN has better HER characteristics, controllable preparation of the materials is still challenging. Herein, selective preparation of γ‐Mo 2 N and δ‐MoN is demonstrated by controlling the spatial stress. The hybrid δ‐MoN and N‐doped carbon composite (MoN/NC) consists of MoN layers and 1‐nm‐thick carbon layers. The carbon layers polarized by the high valence state of Mo in MoN provide the adsorption sites for H + , and the NC layers also facilitate electron transport during the catalytic process. As a result, MoN/NC exhibits remarkable HER activity such as low overpotentials of 93, 211 and 141 mV to attain a current density of 10 mA·cm −2 as well as small Tafel slopes of 44.5, 83.2 and 65.4 mV·dec −1 in acidic, neutral and basic electrolytes of 0.5 mol·L −1 H 2 SO 4 , 1 mol·L −1 PBS, and 1 mol·L −1 KOH, respectively. The spatial stress effects enable selective preparation of specific phases in catalysts, and the pertinent mechanism provides important guidance to the preparation and optimization of advanced catalysts.