Dynamic Quantification of Nitrogen Species in Acidic Titanium-Catalyzed Nitrate Reduction toward Ammonia

The electrochemical reduction of NO3– to NH3 offers a sustainable pathway for nitrogen recycling and can have significant implications for future chemical production. Key challenges in this domain include identifying the transient nature of reactive intermediates and the quantitative measurement of reaction products. These areas are critical for mechanistic insights that can inform future technological development. Here, we report an analysis of NO3– reduction on a metallic Ti surface, enabled by experimental methodologies with exceptional sensitivity and time resolution for the identification and quantification of NO3– reduction species. Combining gas chromatography, ion chromatography, and electrochemical mass spectrometry, we identified and quantified key reduction products (NH4+, H2, NO3–, NO2–, N2O), including difficult-to-detect species NO. Ti electrodes achieved high NH4+ Faradaic efficiency, averaging 82.3% at −1.0 V vs RHE, while for the first time, quantifying detectable NO and N2O. The appearance of NO supports its role as a reaction intermediate, while N2O formation points to an alternative N pathway that does not produce NH3. We also observed increased H2 production, likely linked to Ti hydride formation, that coincides with decreases in NO and N2O production. These findings advance our understanding of NO3– reduction and offer new avenues for rationally designing catalysts that enhance NH4+ selectivity and efficiency.