Tuning the Selectivity for High Yield Ammonia Production in Electrochemical Nitrate Reduction using Sulfur and...

The electrocatalytic nitrate (NO₃ ^-) reduction reaction (NO₃RR) offers a promising pathway for synthesizing value-added ammonia (NH₃) while removing NO₃ ^- pollutants. However, this reaction is hindered by NO₃ ^- adsorption and slow kinetics involving multiple proton and electron transfer steps. In pursuit of an efficient catalyst, a sulfur and nitrogen-rich carbon catalyst, SNC 700, with a cuboidal morphology is presented for selective electrochemical NO₃ ^- reduction to NH₃. The SNC 700 catalyst exhibited a higher NH₃ Faradaic efficiency (F.E.) of 97.83% and an extremely low F.E. of nitrite (NO₂ ^-, ≈ 0.69%) compared to the counterpart NC 700 catalyst (F.E._NH3 42.85%, F.E. _NO2- 9.92%) at a potential of -0.6 V vs. RHE. Complementary insights from in-situ Raman spectroscopy and microelectrochemical studies revealed the reaction pathway, highlighting a rapid reduction of NO₃ ^- intermediate and more favorable hydrogenation over SNC 700 catalyst compared to NC 700. This suggests that incorporating sulfur into the nitrogen-containing carbon structure enhances hydrogen adsorption, leading to improved NO₃ ^- to NH₃ selectivity. This work presents a straightforward and practical approach to address the challenges of limited NO₃ ^- reduction selectivity, particularly for carbon-based materials.