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 (NO3−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 NO3−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 Co3O4 as model system, we reveal that the oxygen vacancies on crystal facet can greatly promote water dissociation and capture HER intermediate for NO3−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 NO3−RR, which provides a significant insight into the catalyst designing and hydrogenation mechanism.