Extended Data Fig. 2: Investigation of the reaction performances by using directly added H₂O₂ and in-situ generated H₂O_2.

a, Schematic overview of N₂ oxidation using in-situ generated H₂O₂ from oxygen reduction reaction (ORR). b, The histogram of HNO₃ formation rates and Faradaic Efficiency with different concentration of FeSO₄ (Typical reaction conditions: 0.25 mol·L⁻¹ Li₂SO₄ with pH adjusted to 3 by H₂SO₄, P_O2/P_N2 =1/1, 0 V vs. RHE). c, The schematic overview that N₂ was oxidated to HNO₃ by ·OH from Fenton reaction. d, The formation rate of HNO₃ at different concentrations of FeSO₄ (8 mol·L⁻¹ of H₂O₂ and 100 mL·min⁻¹ of N₂). The produced trace amount of HNO₃ is due to the use of high concentration H₂O₂ (8 mol·L⁻¹), which can still produce certain amount of OH radicals for N₂ oxidation even in the absence of FeSO₄.

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