Facile, cost-effective plasma synthesis of self-supportive FeSx on Fe foam for efficient electrochemical reduction of N2 under ambient conditions

The electrochemical N-2 reduction reaction (NRR) in an aqueous medium has recently aroused great attention for the synthesis of NH3 under ambient conditions. However, this process generally suffers from a low NH3 production rate and often requires a noble-metal based electrocatalyst with some sophisticated nanosynthesis method. This work reports a new non-precious, self-supportive iron sulfide (FeSx) NRR electrocatalyst, synthesized by a simple H2S-plasma treatment on low-cost Fe foam. The H2S-plasma treatment sulfurizes the Fe surface to afford a self-supportive FeSx thin layer on the Fe foam (FeSx/Fe). The synthesized FeSx/Fe foam can be directly used as the electrode for the NRR, and it is demonstrated to show a remarkable NH3 production rate of 4.13 x 10(-10) mol s(-1) cm(-2) and a high faradaic efficiency of 17.6%, significantly outperforming many other reported non-precious electrocatalysts. Further material characterization shows that the surface FeSx converts to the mackinawite FeS after the NRR; the mackinawite FeS is possibly the actual high-activity NRR electrocatalyst, and density functional theory calculation is further employed to elucidate the NRR mechanism. Given the high performance and low cost, we envision that the plasma-synthesized FeSx/Fe will be of great promise for the electrochemical NH3 synthesis under ambient conditions.