Developing alternative routes for ammonia (NH3) synthesis from nitrogen-containing species under mild conditions is a central challenge in sustainable catalysis. Single-walled carbon nanotubes (SWCNTs) containing intrinsic monovacancy defects provide a distinct class of active sites for electrochemical ammonia (NH3) production. Here, we investigate the reactivity of SWCNT monovacancies in the electrochemical reduction of nitrate (NO3-), nitrite (NO2-), and hydroxylamine (NH2OH) to NH3. We find that NO3- and NO2- reduction proceeds through a single proton-coupled electron transfer (PCET) pathway that requires regeneration of the vacancy site. In contrast, NH2OH reduction can occur through both vacancy-dependent and vacancy-independent mechanisms. At more negative potentials, NH2OH reacts at the regenerated vacancy to form either a ketone and NH3 or an oxime intermediate, which subsequently yields NH3 through additional PCET steps. These results establish SWCNT monovacancies as well-defined model systems for probing reaction mechanisms and guiding the design of efficient electrocatalysts for nitrate-to-ammonia conversion.
Jelušić et al. (Fri,) studied this question.