Mechanism of Ammonia Oxidation to Dinitrogen, Nitrite, and Nitrate on 𝛽-Ni(OH)2 from First-Principles Simulations

The electrocatalyzed ammonia oxidation reaction (AOR) is a potential pathway toward waste ammonia remediation, energy generation, and the synthesis of value- added products. To date, mechanistic studies have focused on elucidating the progress of AOR on Pt-based catalysts with an established pathway for N2 only. In this work, density functional theory was applied to determine the lowest energy intermediates towards nitrogen gas, nitrite, and nitrate formation on 𝛽-Ni(OH)2, a promising electrocatalyst material for AOR. It was found that dinitrogen formation progresses via NH-NH coupling while nitrite and nitrate formation occurs via deprotonation to adsorbed N and subsequent hydroxylation to form oxygenated intermediates. This work is the first to report a mechanism for nitrite and nitrate formation and will also serve as a benchmark for future studies on Ni-based materials.