Scaling Relation of Oxygen Reduction Reaction Intermediates at Defective TiO₂ Surfaces

Abstract

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 surpass conventional catalysts such as Pt in terms of oxygen reduction reaction activity.

Density Functional Theory for Electrocatalysis

“…[231,238] It has been shown that the environmental change of adsorption induces various responses of adsorbed species, [248][249][250] which can be used to search for optimal catalysts beyond the scaling relations. The related tactics to go beyond the scaling relations have been developed and summarized in previous works, [251,252] , such as the doping of the p-block elements, [229,[253][254][255] the secondary adsorption site, [201,256,257] the proton acceptor groups, [258][259][260] the alteration of the local environment around catalytic sites, [261,262] and the change of electrolyte composition. [263][264][265] Lim et al [266] found that the doping of the p-block element causes an extra stabilization of *COOH via stronger bonding interaction between p z orbital of *COOH and S or As doped Agbased catalysts (Figure 6a), which breaks the scaling relation between *COOH and *CO.…”

“…[ 231,238 ] It has been shown that the environmental change of adsorption induces various responses of adsorbed species, [ 248‐250 ] which can be used to search for optimal catalysts beyond the scaling relations. The related tactics to go beyond the scaling relations have been developed and summarized in previous works, [ 251,252 ] , such as the doping of the p ‐block elements, [ 229,253‐255 ] the secondary adsorption site, [ 201,256,257 ] the proton acceptor groups, [ 258‐260 ] the alteration of the local environment around catalytic sites, [ 261,262 ] and the change of electrolyte composition. [ 263‐265 ] Lim et al .…”

The Oxygen Reduction Reaction on Nb-doped Titanium Dioxide Single Crystal Electrodes

“…2 Yamamoto et al predicted that the onset potential of the ORR of TiO 2 doped with Pd or Rh equals to the equilibrium potential of the ORR. 3 These results suggest that TiO 2 electrodes have great potential of new cathode catalysts of fuel cells in the next generation. Many papers reported the ORR on Pt nanoparticles supported on TiO 2 particles.…”

Advances and challenges for experiment and theory for multi-electron multi-proton transfer at electrified solid–liquid interfaces

“…The relation was shown to be applicable to many surfaces where the reaction intermediates take an adsorption structure common to the intermediates. There are, however, exceptions in some cases, including the doped TiO 2 surface, 387 which was expected to be a candidate for a superior electrocatalyst. The simple screening method thus has been successfully applied to many materials, but the success does not automatically justify the assumptions made in the theory; indeed, there are critical arguments.…”