Electrochemical Nitrate Reduction to Ammonia for Boron-Nitrogen Co-Doped Carbon Electrocatalyst in Various Electrolytes

Electrochemical nitrate reduction enables direct NH 3 production from wastewater. Herein, a boron − nitrogen co-doped carbon (BNC) catalyst was synthesized from substituted terpyridine, and the effects of various electrolytes were systematically studied. In 0.1 M HNO 3 , NH 3 Faradaic efficiency (FE) reached ~ 50% at −0.5 to − 0.6 V vs. RHE with negligible intermediate NO 2 − production. In 0.1 M KNO 3 , NO 2 − dominated at low potentials, while NH 3 FE reached ~ 60% at −0.88 V and remained stable to −1.11 V vs. RHE. During 1 −hour electrochemical nitrate reduction reaction (NO₃RR), the electrolyte shifts to an alkaline environment due to proton supply. Adding 0.5 M K 2 SO 4 increased NH 3 yield rate without altering the FE. Further addition of 0.1 M KH 2 PO 4 enhanced proton supply, suppressed NO 2 − production, and increased the NH 3 FE to 72.2% at − 1.17 V and NH 3 yield rate to 435 μmol h −1 mg cat −1 at − 1.25 V vs. RHE. Except for HNO 3 , the yield rate of NH 3 in all electrolytes is linearly related to the electrical charge amount. Using the electrochemical impedance spectroscopy analysis of the various electrolytes, each interface environment between electrolyte and BNC catalyst for the electrochemical NO 3 RR was discussed and clarified. It was demonstrated that increasing proton supply through phosphate adsorption at the interface enhanced the NH 3 FE of the NO₃RR.