Multi-layer core-shell metal oxide/nitride/carbon and its high-rate electroreduction of nitrate to ammonia

The electroreduction of nitrate to ammonia is both an alternative strategy to industrial Haber-Bosch ammonia synthesis and a prospective idea for changing waste (nitrate pollution of groundwater around the world) into valuable chemicals, but still hindered by its in-process strongly competitive hydrogen evolution reaction (HER), low ammonia conversion efficiency, and the absence of stability and sustainability. Considering the unique electronic structure of anti-perovskite structured Fe 4 N, a tandem disproportionation reaction and nitridation-carbonation route for building a multi-layer core-shell oxide/nitride/C catalyst, such as MoO 2 /Fe 4 N/C, is designed and executed, in which abundant Fe-N active sites and rich phase interfaces are in situ formed for both suppressing HER and fast transport of electrons and reaction intermediates. As a result, the sample's NO 3 RR conversion displays a very high NH 3 yield rate of up to 11.10 mol NH 3 g cat. −1 h −1 (1.67 mmol cm −2 h −1 ) with a superior 99.3% faradaic efficiency and the highest half-cell energy efficiency of 30%, surpassing that of most previous reports. In addition, it is proved that the NO 3 RR assisted by the MoO 2 /Fe 4 N/C electrocatalyst can be carried out in 0.50-1.00 M KNO 3 electrolyte at a pH value of 6-14 for a long time. These results guide the rational design of highly active, selective, and durable electrocatalysts based on anti-perovskite Fe 4 N for the NO 3 RR. An anti-perovskite Fe 4 N-based electrocatalyst (MoO 2 /Fe 4 N/C) shows excellent catalytic activity for the NO 3 RR, such as 11.10 mol NH 3 g cat. −1 h −1 NH 3 yield rate with a superior 99.3% faradaic efficiency and the highest half-cell energy efficiency of 30%.