How Ir-Rh Alloys Improve Electrochemical Ammonia Oxidation Activity Studied by Density Functional Theory

The electrochemical ammonia oxidation reaction (AOR) has applications in hydrogen storage and ammonia waste remediation. Using density functional theory, we investigate the mechanism of AOR on Ir, Rh, and their alloys at varied atomic ratios Ir75Rh25, Ir50Rh50, and Ir25Rh75 towards N2(g), NO2–(aq) and NO3–(aq) formation. This work introduces a method for computational alloy design by considering both electronic energy and configurational entropy. The structures considered are selective to N2(g) formation and all favoured *N-N coupling. An Ir50Rh50 alloy was found to reduce the theoretical onset potential for N2(g) formation relative to pure Ir while not exhibiting a downhill coupling step corresponding to catalyst poisoning by *N as shown for pure Rh, consistent with previous experimental work. The formation of NO2–(aq) and NO3–(aq) demand significantly higher potentials, typically limited by the final hydroxylation step before desorption.