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.