(331b) Electrochemical Recycling N from Wastewater Towards Fossil-Free NH3 Production Using Dispersed Ru Atom in Cu Metal Catalyst: An Ab-Initio Study.

The use of fertilizes has led to nitrate buildup in water systems, and now routinely exceed health and safety levels. In this work, we use density functional theory calculations to examine electrolytic nitrate reduction pathways on Ru in Cu single atom alloy (SAA) catalysts as compared to the parent Cu and Ru bulk material. We examine two potential pathways, reduction to N₂, which is useful if the water is to be consumed, or NH₃, which could be used in concentrated water to cyclically produce fertilizes, closing the nitrate cycle with lower energy input. Specifically, we map the minimum reaction pathways for nitrate reduction to N₂, NH₃ and other reduction products on the Cu[111], Ru single atom in Cu[111] and Ru[001] surfaces. The Ru SAA and Ru bulk enhance the electrocatalytic performance because they bind NO₃ more strongly, thus increasing the surface concentration of the desired reactants. Similarly, the Cu catalyst preferentially directs reduction along the N₂ pathway because the N-surface bonds are weaker. Thus the formation of N-N bonds is favored over N-H bonds by 1.0 eV. The Cu-Ru has 0.3 eV smaller reaction barriers for NH bond association as compared to N₂ association. With higher reaction barriers for N₂ and nitrous oxide reaction pathways over Cu-Ru catalyst, it synergistically reduces by-product formation, with selectivity towards NH₃ production. Lastly, we use microkinetic models to build correlations between applied potential and Nitrate concentration to expected reactor performance, showing the criticality of moderate, but not overly high potentials, in order to maximize production of NH₃ or N₂ rather H₂.