Plasma-etching enhanced titanium oxynitride active phase with high oxygen content for ambient electrosynthesis of ammonia

Abstract 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 (TiN BM, BM represents ball-milling) is highly electrochemically active for the nitrogen (N 2 ) reduction reaction (NRR) to NH 3 . The results demonstrate that the TiN-PE as NRR electrocatalyst can deliver a yield rate of NH 3 of 3.32 × 10 −10  mol s −1  cm −2 (4.1 mg h −1  g cat. −1 ) with a Faradaic efficiency of 9.1% at −0.6 V ( vs. RHE) in 0.1 M Na 2 SO 4 solution (pH = 3.2). The X-ray photoelectron spectroscopy (XPS) analysis indicates that the titanium oxynitride (TiO x N y ) with high oxygen content on TiN surface was significantly enhanced by this plasma-etching approach, which is electrocatalytically active species for NRR. The 15 N isotopic labeling experimental results using 15 N 2 as the feeding gas verify that the syntheized NH 3 product during NRR is composed of 15 N in 15 NH 4 + (the enrichement of 64%) and 14 N in 14 NH 4 + (the enrichment of 36%), indicating that the NRR process follows the Mars–van Krevelen mechanism.