Electrochemical reduction of nitrate to ammonia on ultra-stable amorphous Co–P electrocatalyst

Abstract

Electrocatalytic reduction of nitrate (NO3−) to ammonia (NH3) is garnering increasing interest due to its potential to reduce CO2 emissions as a substitute for the Haber-Bosch process, while also mitigating NO3− pollution. However, it remains a challenge to achieve a current density exceeding 300 mA cm−2 while maintaining the stability of catalysts. Additionally, the anodic oxygen evolution reaction, characterized by slow kinetics and high energy barriers, severely impedes the widespread adoption of NH3 formation from NO3− reduction. Therefore, in this study, we introduce amorphous phosphorus-doped cobalt catalysts (Co–P@NF) prepared via a facile electrodeposition process for efficient NO3− reduction and hydrazine oxidation. The incorporation of phosphorus in Co–P@NF facilitates electron migration from phosphorus to cobalt, enhancing *H provision for efficient hydrogenation of the intermediate *NO2−. This results in a current density of 2 A cm−2 at −0.3 V, with a faradaic efficiency for NH3 of 91% in an electrolyte containing 1 M NO3−. Moreover, the Co–P@NF catalyst exhibits remarkable long-term stability, maintaining an NH3 faradaic efficiency exceeding 90% and a current density of 799 mA cm−2 after 82 hours of electrolysis. Furthermore, Co–P@NF displays high catalytic activity in promoting the rate-determining step of hydrazine oxidation, from *N2H2 to *N2H. The incorporation of the HzOR (hydrazine oxidation reaction)-assisted NO3−RR (nitrate reduction reaction) unit significantly reduces the cell voltage to 0.34 V at 300 mA cm−2.