Role of Interfacial Water Structure in the Electroreduction of NO over Cu₂O

The electrochemical nitric oxide reduction reaction (NORR), which utilizes water as the sole hydrogen source, has the potential to facilitate ammonia production while concurrently mitigating pollutants. However, limited research has been dedicated to characterizing the structure of interfacial water due to the challenges associated with probing this intricate system, impeding the development of more efficient catalysts for the NORR process. Herein, the Cu₂O microcrystals with distinct exposed facets, including {100}, {110}, and {111}, are employed for the model catalysts to investigate interfacial water structure and intermediate species in the NORR process. The results from shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) indicated that the NORR performance in 0.1 M Na₂SO₄ (with heavy water as the solvent) was positively correlated to the proportion of hydrated Na⁺ ion water. In addition, a sequence of intermediates from the NORR, including *NOH, *NH, *NH₂, and *NH₃, was detected by employing a combination of multiple <i>in situ</i> characterization methods. Furthermore, in conjunction with experimental results and theoretical calculations, we revealed the potential reaction pathway of NORR. This study offers novel insights into the NORR mechanism and valuable guidance for the design of high-performance catalysts for ammonia production.