Free radicals promote electrocatalytic nitrogen oxidation.

In this work, we introduce hydroxyl radicals into the electrocatalytic nitrogen oxidation reaction (NOR) for the first time. Cobalt tetroxide (Co 3 O 4 ) acts not only as an electrocatalyst, but also as a nanozyme (in combination with hydrogen peroxide producing ˙OH), and can be used as a high-efficiency nitrogen oxidation reaction (NOR) electrocatalyst for environmental nitrate synthesis. Co 3 O 4 + ˙OH shows an excellent nitrogen oxidation reaction (NOR) performance among Co 3 O 4 catalysts in 0.1 M Na 2 SO 4 solution. At an applied potential of 1.7 V vs. RHE, the HNO 3 yield of Co 3 O 4 + ˙OH reaches 89.35 μg h -1 mg cat -1 , which is up to 7 times higher than that of Co 3 O 4 (12.8 μg h -1 mg cat -1 ) and the corresponding FE is 20.4%. The TOF of Co 3 O 4 + ˙OH at 1.7 V vs. RHE reaches 0.58 h -1 , which is higher than that of Co 3 O 4 (0.083 h -1 ), demonstrating that free radicals greatly enhance the intrinsic activity. Density functional theory (DFT) demonstrates that ˙OH not only can drive nitrogen adsorption, but also can decrease the energy barrier (rate-determining step) of N 2 to N 2 OH*, thus producing great NOR activity.