Engineering CoO/Co3O4 Heterostructures Coupled with Adjacent Fe Single Atoms to Boost Tandem Electrocatalytic Nitrate Reduction for High-Efficiency Ammonia Production

Abstract

Electrocatalytic nitrate reduction offers a promising and sustainable technology for ammonia synthesis. However, the different adsorption configurations of *NO3 and *NO2 intermediates pose significant challenges for a single active site to simultaneously optimise their binding energies. A key issue lies in the accumulation of nitrite on the Fe single-atom site, resulting in the sluggish kinetics of the subsequent deoxygenation and hydrogenation steps. To effectively deal with this issue, in this work, a novel tandem catalyst was developed by integrating atomically dispersed Fe single atoms with adjacent CoO/Co3O4 heterostructures to boost the electroreduction of NO3− to NH3. The obtained tandem catalyst structure delivered a remarkable Faradaic efficiency of 99.6% and an exceptional ammonia yield rate of 2.28 mmol h−1 mgcat.−1. Density functional theory calculations were also conducted, indicating that the CoO/Co3O4 heterostructure can efficiently tune the adsorption geometry of nitrite, thereby accelerating the electroreduction of nitrite to ammonia. Through elucidating both the detailed reaction pathway and tandem catalytic mechanism, this work provides valuable insights for the rational design of next-generation single-atom-based eNO3RR electrocatalysts.