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

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. 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.