Decoding the Stability-Activity Paradox in Electrochemical Ammonia Oxidation: An Operando Perspective.

Electrochemical ammonia oxidation reaction (AOR) offers a promising avenue to produce a sustainable energy conversion system through ammonia fuel cell electrolyzers and green hydrogen generation at lower overpotential. Recently, several homogeneous and heterogeneous catalytic systems have been explored to facilitate the ammonia oxidation process. However, its practical applicability is hindered by catalyst instability and degradation under harsh reaction conditions, such as high pH and high anodic potential. Certain associated challenges of electrochemical ammonia oxidation include metal dissolution, leaching, agglomeration-induced catalytic deactivation, and the strong affinity of nitrogenous intermediates with metal sites, leading to catalyst poisoning. Identification of such minute changes occurring at the metal active site or electrode-electrolyte interface requires sophisticated characterization techniques under experimental conditions. Here in this perspective article, we first discuss the mechanistic pathway of AOR, followed by a discussion on noble or non-noble metal-based electrocatalysts for AOR. This perspective critically investigates the central origin of catalyst deactivation during the ammonia oxidation process, thereby portraying the relationship between the coordination geometry, electronic structure, and surface sensitivity, which predominantly governs the electronic long-term stability and functional intensity. Then, various electrochemical in situ techniques, such as in situ X-ray absorption spectroscopy (XAS), Raman spectroscopy, and Fourier transform infrared (FTIR), have been discussed for systematically studying the dynamic evolution of the active site, transient intermediates generated during AOR, and the local electronic and coordination structure of the catalyst. Finally, this perspective outlines future directions for the strategic synthesis of electrocatalysts, operando techniques, and durability engineering to propel the rational development of a sustainable and robust system for ammonia oxidation.