Coupling Anodic Reactions in Electrochemical Nitrate Reduction to Ammonia

Abstract

Ammonia is a widely produced chemical globally, primarily used in fertilizers and chemical products. Recently, it has gained attention as a green hydrogen carrier due to its high hydrogen content and energy density. However, the conventional Haber-Bosch process for ammonia synthesis is energy-intensive, requiring high temperatures and pressures. Also, it is a significant source of CO₂ emissions. To address these environmental concerns, the electrochemical nitrate reduction reaction (NO₃RR) has emerged as a promising approach for green ammonia production, utilizing nitrate from wastewater and renewable energy sources. While most previous research focuses on cathodic ammonia production, it needs to emphasize the importance of optimizing anodic reactions in NO₃RR systems to reduce energy consumption and improve efficiency. The conventional oxygen evolution reaction (OER), typically coupled with NO₃RR, is kinetically slow and requires a high standard potential. Therefore, alternative anodic reactions with lower standard potentials not only save energy but also yield valuable byproducts. Furthermore, coupling NO₃RR with anodic reactions like zinc oxidation allows for power generation, where a positive cell potential indicates spontaneous reactions. This dual approach, energy saving and generation, opens new pathways for sustainable ammonia production, reducing overall energy demands while supporting the shift toward green ammonia systems.