Energy-efficient tandem Nitrate-to-Ammonia electrochemical reduction

Energy-efficient tandem Nitrate-to-Ammonia electrochemical reductionMarcelo Chavez a, Sebastian Murcia a, Joan Ramon Morante aa Catalonia Institute for Energy Research (IREC), Sant Adrià de Besos, 08930, Barcelona, Spain.Materials for Sustainable Development Conference (MATSUS)Proceedings of MATSUS Spring 2024 Conference (MATSUS24)#MatInter - Materials and Interfaces for emerging electrocatalytic reactionsBarcelona, Spain, 2024 March 4th - 8thOrganizers: Marta Costa Figueiredo and María Escudero-EscribanoOral, Marcelo Chavez, presentation 325DOI: https://doi.org/10.29363/nanoge.matsus.2024.325Publication date: 18th December 2023The global transition to sustainable energy sources and the evolution toward a hydrogen-based economy demand energy formats that enable prolonged storage and efficient transportation from remote, renewable energy-rich locations. Liquefied energy forms, notably ammonia (NH3), are gaining favor as viable alternatives, serving not only as a prominent energy carrier but also playing a crucial role as feedstock for the chemical and fertilizer industries. In this context, highly efficient nitrate electroreduction (NO3-RR) emerges as a pivotal process for sustainable NH3 production, promising to overcome limitations associated with the current Haber-Bosch process. However, existing electrocatalysts face significant drawbacks in productivity yield, energy efficiency, and stability, especially under industrial conditions. The NO3-RR process involves an eight-electron transfer assisted by protons, generating multiple intermediates that can diminish overall efficiency, particularly when NH3 is the desired end product. Several studies recognize the reduction of NO3- to nitrite (NO2-) as the rate-determining step (RDE), with subsequent chemical and electrochemical steps occurring after the formation of NO2-. Consequently, at low overpotentials with negligible competition from the Hydrogen Evolution Reaction (HER), the deoxygenation of adsorbed NO2- determines the overall NO3-RR, accentuating the importance of targeting this step to maximize NH3 generation. The accumulation of NO2- intermediate byproducts in the electrolyte necessitates the simultaneous acceleration of NO3-RR and NO2-RR to NH3, presenting a challenging yet promising approach for efficient ammonia generation. This study introduces a tandem NO3-RR process, involving sequential electrochemical processes converting NO3- to NO2- and then NO2- to NH3. An employed composite electrocatalyst of Titanium Dioxide with oxygen vacancies (TiO2-x) deposited on a Copper oxide (I)-copper (Cu2O-Cu) surface, coupled with an optimized flow-cell configuration, produces compelling results toward NH3: a Faradaic Efficiency (FENH3) of 97%, selectivity (SENH3) of 80%, and a productivity yield of 0.45 mmol h-1 cm-2. The cooperative synergy of intrinsic properties of the electrode composition and cell configuration enables high Half-Cell (EENH3) and full-cell (EECELL) energy efficiencies (52% and 43%, respectively). In summary, our tandem NO3-RR process represents a significant advancement in addressing the challenges of sustainable ammonia production, providing a promising and efficient approach for environmentally friendly energy applications. Acknowledgements:IREC also acknowledges support from CERES project (PID2020- 116093RB-C42). M.E.C. acknowledges the Formacion Profesional de Investigadores Program (PRE2018-083575). © FUNDACIO DE LA COMUNITAT VALENCIANA SCITOnanoGe is a prestigious brand of successful science conferences that are developed along the year in different areas of the world since 2009. 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