Built-in-electric field and carbon nanotube supporting enabled Co₃O₄/CeO₂ heterostructures with efficient and durable activities for nitrate-to-ammonia conversion

Development of efficient and durable catalysts for the conversion of nitrate to ammonia is of great significance; however, it remains a great challenge due to the involvement of complex multiple electron-proton transfer steps. This work reports that through built-in-electric field (BIEF) establishment and carbon supporting, aminated doped carbon nanotube supported Co₃O₄/CeO₂ hetero-nanoparticles (Co₃O₄/CeO₂@NCNTs) with high activity and stability for the nitrate-to-ammonia conversion are obtained. The Co₃O₄/CeO₂@NCNTs achieve an NH₃ yield rate of 14.85 ± 0.25 mg h⁻¹ cm⁻² with a Faradaic efficiency (FE) exceeding 97.1 ± 1.6 %, and show no observable activity loss over 120 h of the NO₃^-RR. Their Co₃O₄ mass activity for the NH₃ production is 1.47 times higher than the Co₃O₄@NCNTs. Investigations reveal that the NCNT support enhances the electrical conductivity of the catalyst, thereby lowering the resistance-induced energy losses. Additionally, it facilitates the adsorption of NO₃^- through the electronic coupling between Co₃O₄/CeO₂ and NCNTs. The BIEF promotes the charge redistribution between Co₃O₄ and CeO₂, enhancing the adsorption of NO₃^- on Co₃O₄. CeO₂ promotes the H₂O adsorption and the active hydrogen formation across the Co₃O₄/CeO₂ interface while suppressing the H₂ evolution. It facilitates the hydrogenation steps involved in the nitrate-to-ammonia conversion. Furthermore, the Co₃O₄/CeO₂ heterostructuring contributes to the shortening of the Co-O bond length, thereby increasing the stability of the Co₃O₄/CeO₂@NCNTs. Intriguingly, the Co₃O₄/CeO₂@NCNTs demonstrate great promises for applications in industrial-scale NH₃ production and environment remediation of NO₃^--polluted water.