Balancing Hydrogen Evolution and Hydrogenation Reaction via Facet Engineering for Efficient Conversion of Nitrate to Ammonia in Actual Wastewater

Abstract Due to the competitive relationship between nitrate reduction reaction (NO 3 − RR) and hydrogen evolution reaction (HER), the conventional approach to improve Faradaic efficiency is to select a catalyst without HER activity. Nevertheless, such a strategy not only limits the application of HER catalysts in NO 3 − RR, but also causes insufficient hydrogen source, thereby sacrificing ammonia yield rate. We believe that HER catalysts should not be excluded from hydrogenation reduction. Herein, taking traditional water electrolysis material Co 3 O 4 as model system, we reveal that the oxygen vacancies on crystal facet can greatly promote water dissociation and capture HER intermediate for NO 3 − RR, successfully shifting the reaction pathway from hydrogen evolution to nitrate hydrogenation. Beyond material development, we construct a hybrid reactor and achieve an ammonia recovery rate of 1216.8 g‐N m −2 d −1 in nuclear industry wastewater with ultra‐high nitrate concentration. This study breaks through the limitation of HER catalyst in NO 3 − RR, which provides a significant insight into the catalyst designing and hydrogenation mechanism.