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Electrocatalytic synthesis of ammonia from nitrate reduction: the role of copper and its oxides as efficient catalysts

Abstract

The electrocatalytic synthesis of ammonia from the reduction of nitrate ions has emerged as a promising technology to replace the energy-intensive Haber-Bosch process. Ammonia can be synthetized electrochemically with interesting efficiencies and formation rate values, and when coupled with a sustainable energy matrix, a "green" seal can be obtained. Among several metals, Cu has shown the fastest rate-determining step of nitrate to nitrite, the highest electrocatalytic reduction kinetics and weak hydrogen evolution ability in low overpotentials. When combining it with Cu oxides, an outstanding activity and selectivity is observed for the formation of ammonia. Atomistic calculations have reported the stabilization of NOHad intermediate as the main responsible for the excellent performance to ammonia production, going through successive reduction steps to hydroxylamine and then ammonia. We propose in this project the electrosynthesis of ammonia from the reduction of nitrate ions on Cu-based oxides as electrocatalysts with different surface and bulk compositions. The idea relies on the better understanding of why copper and its oxides seem to catalyze the reaction effectively. For this aim, we intend to apply in situ (FTIR and Raman) and on line (DEMS and GC) techniques coupled to the electrochemical cell in order to monitor the molecular aspects of the reaction and in combination with the physical characterization of the catalyst (TEM, XPS, XRD, AFM, etc), draw a close correlation between the material properties with the electrocatalysis of the nitrate reduction reaction. The synergic combination of the expertise of both proponents of this project will facilitate a deeper mechanistic investigation of energy conversion reactions, aiming the development of more efficient and selective catalysts. As an additional outcome, a long-term joint cooperation will be strengthened. (AU)

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