Hydrophilic engineering of VO_X-based nanosheets for ambient electrochemical ammonia synthesis at neutral pH

Achieving fast electrocatalytic nitrogen reduction reaction (NRR) at ambient conditions has an important implication to the low-cost synthesis of ammonia, a paramount raw material for agricultural and chemical industries. However, ambient NRR is severely challenged by the lack of active electrocatalysts and a serious competition between hydrogen evolution reaction (HER) and NRR. Herein, we report a low-cost, oxygen-deficient, and multivalent vanadium oxide (mVO_x) nanosheets mixed with reduced graphene oxide (rGO) as an active electrocatalyst for NRR. The testing results show a high ammonia yield of 18.84 μg h^-1 mg_cat.^-1 and a remarkable faradaic efficiency of 16.97% at -0.35 V versus reversible hydrogen electrode in a neutral 0.1 M Na₂SO₄ electrolyte. The outstanding performance is correlated by theoretical calculations to the hydrophilicity and high concentration of oxygen vacancies in mVO_x, which promote nitrogen/water activation and lower the energy barrier for NRR. The presented insights of tailoring hydrophilicity via defect engineering are expected to significantly influence future designs of high-performance NRR electrocatalysts.