Energy-efficient electrochemical ammonia production from dilute nitrate solution

Abstract

Highly efficient electrochemical nitrate reduction could become a key process for sustainable ammonia production overcoming many limitations of the Haber-Bosch process. Current state-of-the-art electrocatalysts have severe drawbacks regarding yield, selectivity and energy efficiency when dealing with dilute nitrate solutions. Herein, we report a layered double hydroxide (LDH)/Cu foam hybrid electrocatalyst that offers a potential solution to this challenge. The [Ni0.75Fe0.25(OH)(2)](CO3)(0.125) (Ni3Fe-CO3 LDH) exhibits an appropriate kinetic energy barrier for the Volmer step generating hydrogen radicals as well as suppressing H-H bond formation by inhibition of the Heyrovsky step. The electrochemically generated hydrogen radicals transfer to a Cu surface enabling NO3- reduction to NH3. The Ni3Fe-CO3 LDH/Cu foam hybrid electrode exhibits an 8.5-fold higher NH3 yield compared to a pristine Cu surface, while exhibiting an NH3 selectivity of 95.8% at 98.5% NO3- conversion. The best half-cell energy efficiency (36.6%) was recorded while achieving 96.8% faradaic efficiency at -0.2 V in 5 mM NO3(aq)-.