Here we report that the plasma-etching processed commercial titanium nitride (TiN-PE, PE represents plasma-etching) that was first treated by ball-milling method (TiNBM, BM represents ball-milling) is highly electrochemically active for the nitrogen (N2) reduction reaction (NRR) to NH3. The results demonstrate that the TiN-PE as NRR electrocatalyst can deliver a yield rate of NH3 of 3.32 × 10−10 mol s−1 cm−2 (4.1 mg h−1 gcat.−1) with a Faradaic efficiency of 9.1% at −0.6 V (vs. RHE) in 0.1 M Na2SO4 solution (pH = 3.2). The X-ray photoelectron spectroscopy (XPS) analysis indicates that the titanium oxynitride (TiOxNy) with high oxygen content on TiN surface was significantly enhanced by this plasma-etching approach, which is electrocatalytically active species for NRR. The 15N isotopic labeling experimental results using 15N2 as the feeding gas verify that the syntheized NH3 product during NRR is composed of 15N in 15NH4+ (the enrichement of 64%) and 14N in 14NH4+ (the enrichment of 36%), indicating that the NRR process follows the Mars–van Krevelen mechanism.