Electrocatalytic reduction of nitrogen oxyanions (NO_x⁻ , x =3 and 2) to ammonia (NH₃) under ambient conditions is an alternative to the Haber-Bosch process (HBP). Recent catalysts are vulnerable to low-rate and -selectivity NH₃ synthesis due to the multi-step electron–proton transfer process and water as a proton donor, especially in neutral media. Herein, we introduce sulfur species into Co₃O₄ spinel nanosheets (S-Co₃O₄) inspired by the bio-nitrogenase of metal-sulfur clusters to alleviate the above dilemma. The S₅-Co₃O₄ exhibits an NH₃ yield rate of 174.2 mmol h⁻¹ g⁻¹ at − 0.6 V versus reversible hydrogen electrode (RHE) with a Faradaic efficiency of 89.9 %, nitrate (NO₃⁻ ) as feedstock. Furthermore, nitrite (NO₂⁻) reduction possesses comparable NH₃ Faradaic efficiency (87.6 %) and a higher yield rate (314.5 mmol h⁻¹ g⁻¹) at the same conditions. Theoretical calculations demonstrated that sulfur species reduce the free energy change of formation *H, boosting the activation of *NO_x (x = 3 and 2). A two-electrode device, S₅-Co₃O₄ as bifunctional catalysts, demonstrates excellent NH₃ Faradaic efficiency (>95 %) over a wide voltage range for NO₂⁻ RR, while the anode produces high value-added benzoic acid.