Energy-efficient electrochemical ammonia production from dilute nitrate solution

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 [Ni 0.75 Fe 0.25 (OH) 2 ](CO 3 ) 0.125 (Ni 3 Fe-CO 3 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 NO 3 − reduction to NH 3 . The Ni 3 Fe-CO 3 LDH/Cu foam hybrid electrode exhibits an 8.5-fold higher NH 3 yield compared to a pristine Cu surface, while exhibiting an NH 3 selectivity of 95.8% at 98.5% NO 3 − conversion. The best half-cell energy efficiency (36.6%) was recorded while achieving 96.8% faradaic efficiency at −0.2 V in 5 mM NO 3 − (aq) . Highly efficient electrochemical nitrate reduction could be key for sustainable ammonia production. Our NiFe LDH/Cu foam electrode exhibits an NH 3 selectivity of 95.8% with 98.5% nitrate conversion.