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

Abstract

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 Fe₄N, a tandem disproportionation reaction and nitridation–carbonation route for building a multi-layer core–shell oxide/nitride/C catalyst, such as MoO₂/Fe₄N/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 NO₃RR conversion displays a very high NH₃ yield rate of up to 11.10 mol_NH3 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 NO₃RR assisted by the MoO₂/Fe₄N/C electrocatalyst can be carried out in 0.50–1.00 M KNO₃ 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 Fe₄N for the NO₃RR.