(186d) Indium (Hydroxy)Oxide Films on Platinum Nanoparticles for CO Electrooxidation

The submonolayer deposition of metal (hydroxy)oxide materials on platinum surfaces has been shown to result in strong catalytic performance for bifunctional reaction mechanisms such as electrochemical CO oxidation in alkaline environments. Reducible 3d transition metal (hydroxy)oxides have been investigated for these reactions due to their ability to adsorb OH^- from the electrolyte or to change their oxidation state to produce the neutral OH_ad intermediate. However, in our recent experimental work, we showed that indium, a post-transition metal for which reduction is thermodynamically unfavorable under CO oxidation conditions, outperformed 3d transition metals for CO oxidation, giving an overpotential of ~200 mV lower than pure Pt. These findings indicate that indium oxide surfaces may allow for the facile cleavage of HO – H bonds in H₂O, thereby improving CO oxidation activities.

In this work, we employ first-principles calculations on various indium (hydroxy)oxide films on a Pt(111) substrate to explain the process by which this system achieves low overpotentials for CO electrooxidation. Our results show that the stability range of indium (hydroxy)oxide phases is modified when these phases are present as a monolayer on Pt(111) as compared to the range of stabilities predicted from bulk energetics alone. Further, phases that have been underexplored in the literature, such as InOOH and In(OH)₃, are shown to be relevant under CO oxidation conditions. In addition, hydroxylated In₂O₃(111) demonstrated distinctive stability trends as compared to films of In₂O₃ alone. The effect of the stability trends in these unique surface phases on CO oxidation are then analyzed, and the results are used to explain the low, observed experimental overpotential. These results suggest that this indium catalyst may be suitable for other bifunctional, electrochemical reactions such as the hydrogen evolution reaction, and also argue for the consideration of metals beyond transition metals for similar reactions.