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.