Electrocatalytic Nitric Oxide Reduction to Yield Ammonia over Fe₃C Nanocrystals

Nitric oxide (NO), which generally originates from vehicle exhaust and industrial flue gases, is one of the most serious air pollutants. In this case, the electrochemical NO reduction reaction (NORR) not only removes the atmospheric pollutant NO but also produces valuable ammonia (NH₃). Hence, through the synthesis and modification of Fe₃C nanocrystal catalysts, the as-obtained optimal sample of Fe₃C/C-900 was adopted as the NORR catalyst at ambient conditions. As a result, the Fe₃C/C-900 catalyst showed an NH₃ Faraday efficiency of 76.5% and an NH₃ yield rate of 177.5 μmol·h^–1·cm^–2 at the working potentials of –0.8 and –1.2 V versus reversible hydrogen electrode (vs. RHE), respectively. And it delivered a stable NORR activity during the electrolysis. Moreover, we attribute the high NORR properties of Fe₃C/C-900 to two aspects: one is the enhanced intrinsic activity of Fe₃C nanocrystals, including the lowering of the energy barrier of rate-limiting step (*NOH→*N) and the inhibition of hydrogen evolution; on the other hand, the favorable dispersion of active components, the effective adsorption of gaseous NO, and the release of liquid NH₃ products facilitated by the porous carbon substrate.