surfaces

Enhancing the oxygen reduction reaction (ORR) is a major topic of electrocatalysis, and surfaces have long been designed to realize a full alignment of the adsorption energies of the reaction intermediates, O2*, O*, OH* and OOH*. The alignment is not easy to realize because the adsorption energies often change obeying a linear relationship among them, known as the scaling relation, rather than change independently by modifying the surface. Pristine oxide surfaces tend to show the scaling relation [1], but defective TiO₂, attracted attention as the electrocatalyst beyond Pt, may behave exceptionally because of the measured high reactivity.
Our density functional calculations have shown that OH* and OOH* on defective TiO₂ surfaces follow the same scaling relation found for typical pristine oxide surfaces, suggesting defective TiO₂ is not closer to the ideal catalyst. To our surprise, however, there are metastable surfaces whose pristine surfaces exhibit a significantly deviated relation. This exceptional behavior is related to the fact that those surfaces let OOH* dissociate into O* at a two-folded O site and OH* at a Ti. The deviation from the scaling relation suggests a possibility towards realizing an ideal catalyst.

[1] I. C. Man et al., ChemCatChem 3, 1159(2011).