Scaling Relation of Oxygen Reduction Reaction Intermediatesat Defective TiO 2 Surfaces

Enhancing the oxygen reduction reaction is a major topic of electrocatalysis research. The maximal enhancement is achieved, within the thermodynamic argument, by aligning the adsorption free energies of reaction intermediates so that energy barriers along the reaction path are minimized. Full alignment is, however, difficult to realize. This is due to the linear scaling relation between the adsorption energies of intermediates along the reaction path, which has been observed almost universally in electrocatalyst materials including Pt. Thus, finding a way to deviate from this universal relation is an important issue in the catalyst design. Here, we investigate such possibility by studying TiO2 surfaces modified with substitutional dopants or oxygen vacancies. Our density functional calculations suggest that universal scaling is violated on TiO2, particularly when the adsorbent forms bonds not only with a metal atom but also with a lattice oxygen atom. This fact suggests that TiO2 has the potential to surp...