Computational Screening of Rutile Oxides for Electrochemical Ammonia Formation

Industrial scale production of ammonia at ambient conditions represents a potential economic and environmental break-through. By mimicking the naturally occurring enzymatic process, ammonia could be produced electrochemically from N-2 and water. To date, no such mechanism has come close to the production rates required for commercial viability. In this article, we present the results of a screening for possible catalysts, where density functional theory (DFT) calculations were performed on 11 transition metal dioxides in the rutile structure. The aim was to find candidates that were stable and active toward ammonia formation while simultaneously suppressing the competing reaction of H-2 evolution. The most promising rutile oxide candidates are found to be the (110) facets of NbO2, ReO2 and TaO2, showing promise of producing ammonia at relatively low onset potentials of -0.57 V, -1.07 V and -1.21 V vs the standard hydrogen electrode, respectively. IrO2 was found to be the most active catalyst for this reaction with an onset potential of -0.36 V, but its surface might be poisoned by adsorbed hydrogen atoms.