Filling the nitrogen vacancies with sulphur dopants in graphitic C3N4 for efficient and robust electrocatalytic nitrogen reduction

Exploring active and durable metal-free electrocatalysts represents a promising direction for electrocatalytic N-2 reduction reaction (NRR). Herein, by filling the nitrogen vacancies (NVs) with S dopants in graphitic C3N4, we showed that the resultant S-NV-C3N4 could be an efficient and robust metal-free NRR catalyst in neutral solution. S-NV-C3N4 with a high S concentration of 5.2 at.% exhibited a fascinating NRR performance with an NH3 yield of 32.7 mu g h(-1) mg(-1) and a Faradaic efficiency of 14.1 % at -0.4 V (vs. RHE), considerably outperforming pristine C3N4 and NV-containing C3N4. S-NV-C3N4 also showed exceptional durability for at least 20 h, in stark contrast to the inferior stability of NV-containing C3N4. Density functional theory calculations disclosed that the filled S dopants could break the scaling relation to effectively stabilize *N2H and destabilize *NH2 on S-NV-C3N4, leading to more optimized adsorption of NRR intermediates and a significantly reduced energy barrier. Meanwhile, the competitive HER can be effectively suppressed on S-NV-C3N4 due to the high energy barrier for water dissociation.