Nitrite Electroreduction to Ammonia Promoted by Molecular Carbon Dioxide with Near‐unity Faradaic Efficiency

Abstract

Electrochemical reduction of nitrite (NO 2 À ) offers an energy-efficient route for ammonia (NH 3 ) synthesis and reduction of the level of nitrite, which is one of the major pollutants in water. However, the near 100 % Faradaic efficiency (FE) has yet to be achieved due to the complicated reduction route with several intermediates. Here, we report that carbon dioxide (CO 2 ) can enhance the nitrite electroreduction to ammonia on copper nanowire (Cu NW) catalysts. In a broad potential range (À 0.7 ~À 1.3 V vs. RHE), the FE of nitrite to ammonia is close to 100 % with a 3.5-fold increase in activity compared to that obtained without CO 2. In situ Raman spectroscopy and density functional theory (DFT) calculations indicate that CO 2 acts as a catalyst to facilitate the *NO to *N step, which is the rate determining step for ammonia synthesis. The promotion effect of CO 2 can be expanded to electroreduction of other nitro-compounds, such as nitrate to ammonia and nitrobenzene to aniline.

Multicomponent catalyst design for CO2/N2/NOxelectroreduction

“…In addition, electroreduction of other NO x molecules, such as NO ( x = 1) and NO 2 − ( x = 2), to NH 3 has been also reported but will not be discussed in the current review. 25–28…”

Recent developments and prospects for engineering first-row transition metal-based catalysts for electrocatalytic NOx− reduction to ammonia

“…Sun's group demonstrated that the faradaic efficiencies of copper catalysts could reach approximately 100% for NO 2 − reduction within a wide range of potentials assisted by CO 2 . 74 The causes of the enhanced performance due to CO 2 are described in Fig. 7c.…”