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

Abstract

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 ($$, $$, and $$) toward $$(g), $$(aq), and $$(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 $$(g) formation and all favored *N–N coupling. An $$ alloy was found to reduce the theoretical onset potential for $$(g) formation relative to pure Ir while not exhibiting a downhill coupling step corresponding to catalyst poisoning by *N as shown for pure Rh, consistent with previous experimental work. The formation of $$(aq) and $$(aq) demand significantly higher potentials, typically limited by the final hydroxylation step before desorption.