Shifting hydrogenation pathway via electronic activation for efficient nitrate electroreduction to ammonia in sewages

Abstract

Electrochemical hydrogenation reactions have attracted worldwide attention as a sustainable alternative to thermo-catalytic hydrogenations. Nevertheless, the Faradaic efficiency, in many cases, is limited by the competing side reaction of hydrogen evolution. In this work, we demonstrate that the hydrogenation pathway can be effectively modulated by electronic activation near the interface. In a heterostructure consisting of a Cu foam matrix and Co₃O₄ decoration layer (Co@Cu), the surface Co is effectively activated by electrons transferring from underneath Cu, leading to strongly promoted reactant adsorption and weakened Co-H bonding. Consequently, the hydrogenation pathway on the Co site shifts from H-H coupling to nitrate reduction, resulting in an outstanding nitrate reduction reaction (NO₃⁻RR) Faradaic efficiency of 97.67%. A hybrid reactor combining electroreduction and membrane separation is further constructed to realize an NH₃ recovery rate as high as 857.1 g-N m⁻² d⁻¹ from actual sewage. The results can be generalized for other electrochemical hydrogenation reactions for energy and environment applications.