Deep Electron Redistributions Induced by Dual Junctions Facilitating Electroreduction of Dilute Nitrate to Ammonia

Abstract The electronic states of metal catalysts can be redistributed by the rectifying contact between metal and semiconductor e.g., N‐doped carbon (NC), while the interfacial regulation degree is very limited. Herein, a deep electronic state regulation is achieved by constructing a novel double‐heterojunctional Co/Co 3 O 4 @NC catalyst containing Co/Co 3 O 4 and Co 3 O 4 /NC heterojunctions. When used for dilute electrochemical NO 3 − reduction reaction (NO 3 RR), the as‐prepared Co/Co 3 O 4 @NC exhibits an outstanding Faradaic efficiency for NH 3 formation (FE NH3 ) of 97.9%, –0.4 V versus RHE and significant NH 3 yield of 303.5 mmol h −1 g cat −1 at –0.6 V at extremely low nitrate concentrations (100 ppm NO 3 − ‐N). Experimental and theoretical results reveal that the dual junctions of Co/Co 3 O 4 and Co 3 O 4 /NC drive a unidirectional electron transfer from Co to NC (Co→Co 3 O 4 →NC), resulting in electron‐deficient Co atoms. The electron‐deficient Co promotes NO 3 − adsorption, the rate‐determining step (RDS) for NO 3 RR, facilitating the dilute NO 3 RR to NH 3 . The design strategy provides a novel reference for unidirectional multistage regulation of metal electronic states boosting electrochemical dilute NO 3 RR, which opens up an avenue for deep electronic state regulation of electrocatalyst breaking the limitation of the electronic regulation degree by rectifying contact.