Bifunctional Cofe-Spinel@Cu for Peroxymonosulfate Activation and Electrochemical Nitrate Reduction Towards High Purity Ammonia Production

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Ammonia is a valuable chemical feedstock and energy carrier with lower corbon footprint during conversion to H2. Haber-Bosch process is the predominant method for industrial NH3 production, but it is associated with high energy consumption and substantial CO2 emission. Recently, electrochemical nitrate reduction reaction (NO3RR), powered by renewable energy in ambient condition, has emerged as a promising method for sustainable NH3 production from nitrate containing wastewater. However, the purity of generated NH3 by NO3RR is also a critical issue that has been overlooked in state-of-the-art reports. In the case of nuclear and steelmaking wastewater, abundant nitrate ions and organic pollutants coexist. Therefore, additional step is required to separate the NH3 generated by the NO3RR from the wastewater matrix. Herein, we designed a coupled NO3RR-PMS activation electrocatalytic system to achieve a high-purity NH3 production. CoFe-spinel on Cu foam (CoFe/CF) was employed both as a cathode for NO3RR and catalyst for chemical PMS activation. The CoFe-spinel was prepared through a straightforward hydrothermal deposition on Cu foam, followed by cathodization in nitrate solution. It achieved 90% faradaic efficiency for NO3 --to-NH3 conversion and NH3 production rate of 1.10 mmol h-1 cm-2 at -0.4 V RHE, together with long-term durability for about 150 h (in 0.1 M nitrate solution at pH 14). Additionally, it demonstrated approximately 90% efficiency in removing organic pollutants via PMS activation (with 10 mg L-1 SMX solution at pH 14). Thus, the coupled NO3RR-PMS activation system, utilizing the CoFe/CF catalyst, produced NH3 with a high purity. The cathodization step generated CoFe2O4 nanostructure with well-developed oxygen vacancies, to provide plentiful active hydrogen for the observed cutting-edge figures of merit for NO3 --to-NH3 conversion. Operando analysis based on X-ray absorption spectroscopy is ongoing to reveal the genuine active site for PMS activation or NO3RR. The proposed system would offer an efficient technology for high-purity NH3 production from nitrate wastewater.