Theoretical Trends in Particle Size Effects for the Oxygen Reduction Reaction

Abstract

Density Functional Theory / Oxygen Reduction Reaction / Structure Sensitivity / Nanoparticles / Size EffectA simple, first principles-based model of the oxygen reduction reaction (ORR) is used to determine ORR kinetics on the (111), (100), and (211) facets of eleven transition metals (Au, Ag, Pt, Pd, Ir, Cu, Rh, Ni, Ru, Co, Fe). For most metals, the unreconstructed (100) facets are found to have an activity comparable to, or slightly higher than, the (111) facets. In contrast, (211) steps are found to be significantly less active than the terraces, with the exception of the most noble metals. These results are combined with simple models of the geometries of catalytic nanoparticles to estimate the average ORR activity of Pt and Au nanoparticles of various sizes. On Pt, a modest decrease in the activity with decreasing particle size is predicted, while for Au, the opposite trend is found.

Origin of Oxygen Reduction Reaction Activity on “Pt3Co” Nanoparticles: Atomically Resolved Chemical Compositions and Structures

“…On the other hand, increasing the {100} and {111} step densities on the {111} and {100} terraces has shown to improve ORR activity in 0.1 M HClO 4 . 45,46 It should be noted that these experimental findings are not in agreement with recent DFT results, 86 which show that lowering the coordination number of surface atoms from low-index to high-index surfaces leads to stronger binding of oxygenated species and thus yields lower ORR activity. For example, high-index {211} surface with {100} steps on the {111} terrace is predicted to have lower ORR activity than the {111} surface.…”

Oxygen reduction reaction on stepped platinum surfaces in alkaline media

“…It is clear that this previous model is not able to reproduce the observed behavior at potentials below 0.82 V. In this model, adsorbed OH is considered as a poison, however, all the DFT models consider adsorbed OH as an intermediate of the 15 reaction. [53][54][55][56] Additionally, the OH coverage is very high at the upper potential limit for all the studied electrodes, and the number of free sites would be negligible. If the free sites were the only sites contributing to the ORR, their intrinsic activity of these sites would be unprecedentedly high.…”

Understanding the electrocatalysis of oxygen reduction on platinum and its alloys

“…Nonetheless, in contrast to experiments on single crystals, we find no evidence to suggest that steps or other undercoordinated sites can increase the ORR activity of Pt nanoparticles. 65,109,114 Stability. Stabilising Pt nanoparticles in the cathode of a fuel cell seems to be even more challenging than controlling their activity.…”