From Raman Spectral Fingerprints to Interfacial Diagnostics in Nitrate Electroreduction.

Electrochemical nitrate reduction to ammonia couples nitrogen-pollutant remediation with sustainable ammonia synthesis, yet its complex interfacial reaction network remains difficult to resolve. In situ Raman spectroscopy provides access to aqueous interfacial chemistry, adsorbed NOx species, dynamic catalyst phases, and local microenvironments under operating conditions. However, many studies still rely mainly on peak assignment, even though the mechanistic reliability of individual spectral features varies substantially. This Perspective presents a Raman-centered diagnostic framework for nitrate electroreduction. Raman signals are organized into four interfacial readouts: adsorbed nitrate and nitrite species, hydrogenated nitrogen intermediates, catalyst reconstruction, and interfacial water and ion structures. An evidence hierarchy is introduced to assess Raman assignments through isotope labeling, potential-, time-, and space-resolved measurements, multimodal validation, and quantitative correlations with product distributions. Emerging opportunities in evidence-ranked spectral atlases, interpretable data-driven analysis, and online Raman monitoring are also discussed. By moving beyond isolated spectral fingerprints, in situ Raman spectroscopy serves as a dynamic interfacial probe for understanding, comparing, and ultimately controlling nitrate electroreduction.