(639a) New Insights into Electrochemical Ammonia Oxidation on Transition Metals from First Principles

Electrooxidation of ammonia to dinitrogen plays a crucial role within the nitrogen transformation cycle. It has many applications including electrochemical sensing of ammonia, wastewater remediation, and direct ammonia fuel cells. While platinum (Pt) based catalysts, specifically terminated with (100) facets, have shown promising activity. They still suffer from a large overpotential (~0.5 V) and surface deactivation¹. One approach that has been utilized to tackle these issues is the use of platinum based alloys. While these alloys have shown some improvements compared to pure platinum catalysts, the lack of a clear mechanistic understanding of ammonia electrooxidation at the electrode/electrolyte interface has hindered significant improvements. Using Grand-Canonical Density Functional Theory (GC-DFT)², we investigate the reaction mechanism at the electrode/electrolyte interface under constant potential conditions for various transition metals and surface terminations.

The thermodynamics for NH₃ oxidation to N₂ on various transition metals was mapped out, and kinetic barriers for dimerization reactions were calculated through GC-DFT. These results are used to understand the superior activity of platinum amongst the transition metals. In addition we will rationalize some of the experimental results that were observed for platinum based alloys. Lastly some of the key mechanistic insights will be highlighted which can then be exploited in new strategies to design more active, selective and robust electrocatalysts for ammonia oxidation

1. Katsounaros, I. et al. On the mechanism of the electrochemical conversion of ammonia to dinitrogen on Pt(1 0 0) in alkaline environment. J. Catal. 359, 82–91 (2018).
2. Pillai, H. S. & Hongliang, X. New Insights into Electrochemical Ammonia Oxidation on Pt(100) from Grand-Canonical Density Functional Theory. Ind. Eng. Chem. Res. Submitted.