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

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/Co₃O₄@NC catalyst containing Co/Co₃O₄ and Co₃O₄/NC heterojunctions. When used for dilute electrochemical NO₃ ^- reduction reaction (NO₃RR), the as-prepared Co/Co₃O₄@NC exhibits an outstanding Faradaic efficiency for NH₃ formation (FE_NH3) of 97.9%, -0.4 V versus RHE and significant NH₃ yield of 303.5 mmol h^-1 g_cat ^-1 at -0.6 V at extremely low nitrate concentrations (100 ppm NO₃ ^--N). Experimental and theoretical results reveal that the dual junctions of Co/Co₃O₄ and Co₃O₄/NC drive a unidirectional electron transfer from Co to NC (Co→Co₃O₄→NC), resulting in electron-deficient Co atoms. The electron-deficient Co promotes NO₃ ^- adsorption, the rate-determining step (RDS) for NO₃RR, facilitating the dilute NO₃RR to NH₃. The design strategy provides a novel reference for unidirectional multistage regulation of metal electronic states boosting electrochemical dilute NO₃RR, which opens up an avenue for deep electronic state regulation of electrocatalyst breaking the limitation of the electronic regulation degree by rectifying contact.