Insights into the role of cation vacancy for significantly enhanced electrochemical nitrogen reduction

Electrochemical nitrogen reduction reaction (NRR) at ambient conditions offers a promising picture for renewable production of ammonia (NH₃), but its practical implementation is strictly restricted by lacking efficient catalysts. Defect engineering as an effective strategy has been applied to promote the electrochemical NRR activity. Unfortunately, in contrast to anion vacancy, the study of cation vacancy for insight into the relationship between the activity and structure of NRR electrocatalysts is still very scarce. Herein, we designed a superior cation-vacancy NRR electrocatalyst by fabrication of MoN nanocrystals with abundant Mo vacancies embedded in N-doped hierarchical porous carbon framework for the first time. Compared with the pre-reported anion-vacancy electrocatalysts, it exhibits an impressive improvement for NRR activity (NH₃ yield: 76.9 μg h⁻¹ mg⁻¹_cat.). We identified Mars-van Krevelen pathway during NRR process by joint ¹⁵N₂ isotopic tracer experiments with nuclear magnetic resonance spectroscopy. First-principles calculations revealed the critical role of Mo vacancy in regulating the electronic properties of MoN and shifting the rate-limiting step of NRR that significantly reduces the reaction barrier. Our findings of creating cation defects in nitrides to catalyze N₂ fixation pave a new avenue for synthesizing realistic and high-efficiency NRR electrocatalysts.