Yamauchi and her group recently showed that anatase type TiO₂ electrodes can be used for electrochemical reduction of carboxylic acids to alcohols [1]. So far this reaction was demonstrated only for oxalic acid with an efficiency very sensitive to the preparation conditions of the anatase electrode. One possible explanation of such sensitivity electrochemical activity to preparation conditions is that the morphology of the surface has deep impact on the electrochemical processes. To improve the efficiency as well as to understand what factors limit the reduction of other acids, we studied the effect of morphology on the electronic structure of anatase nanoparticles using Density Functional Tight Binding (DFTB) method. Since only nanoparticles of anatase up to 5 nm are thermodynamically stable, we focused on nanoparticles of 2-4 nm and assumed that morphological differences of the electrodes can be described with the help of such particle models.

The edges and peaks of nanoparticles contains of 4- and 5- coordinated Ti ions, which can be responsible for smaller band gap and strong reactivity of the particles. We performed extensive calculations to study the water and acid absorption on the edges and faces of nanoparticles to identify the most probable coordination environment of these Ti ions. We also studied the energy and overlap between LUMO (conduction band) of the nanoparticles and substrates, as these orbitals play important role in electrochemical reduction reactions. Our computational work offers new understanding for optimization of titania electrode surfaces for electrochemical reaction.

The work was supported by CREST, JST and the computations were partially performed using Research Center for Computational Science, Okazaki, Japan.

Reference:

[1] R. Watanabe, M. Yamauchi, M. Sadakiyo, R. Abe and T. Takeguchi, Energy Environ. Sci., 2015, 8,

1456–1462