Revealing the kinetics characteristics of low-temperature electrocatalytic ammonia oxidation reaction

Abstract

Electrocatalytic ammonia oxidation reaction (AOR) serves as a critical pathway for the direct utilization of ammonia energy at low-temperature. However, its reaction kinetic mechanism is complicated, and quantitative characterization under multiple operating conditions remains insufficient. In this study, electrochemical tests combined with in situ surface-enhanced Raman spectroscopy (SERS) are first conducted to investigate the variation laws of AOR process and kinetic characteristics under multiple operating conditions. An extra nitrogen redox cycle pathway, distinct from the Gerischer-Mauerer mechanism, is identified during the PtIr-catalyzed AOR process, in which the intermediate N3− strongly adsorbs onto Pt, occupying active sites and thereby reducing the AOR rate. Key kinetic parameters including exchange current density and transfer coefficient, are derived from the comprehensive experimental data to elucidate their evolutionary trends under complex operating conditions. Furthermore, the functional relationship between onset potential, exchange current density, and operating parameters is analyzed, enabling the prediction of key kinetic parameters under specific operating condition, which could provide important theoretical support for understanding and improving the devices involving AOR such as direct ammonia fuel cell and ammonia electrolysis cell.