Selectivity Control of the Photo-Catalytic Water Oxidation on SrTiO₃ Nanocubes via Surface Dimensionality

The role of surface dimensionality in photo-electrochemical water oxidation was studied for different-sized SrTiO3 nanocubes. The band gap illumination of strontium titanate electrodes results in anodic current; the photo-current appears at a bias of ca. 220 mV with respect to flat-band potential. The bias needed to record anodic photo-current increases with pH, reflecting the change in the protonation of surface oxygen atoms. The photo-electrochemical activity of SrTiO3 nanocubes is size-dependent and increases with increasing particle size. Semiquantitative analysis of the observed photo-currents combined with mass spectrometric detection of the reaction products shows that the contact of water with illuminated SrTiO3 nanocubes leads to the formation of oxygen, hydrogen peroxide, and ozone. Oxygen and ozone are the primary products of the water oxidation proceeding on {100}-oriented SrTiO3 faces and their fractions increase with increasing particle size. The hydrogen peroxide is simultaneously produced via oxygen reduction at the low-dimensionality sites (crystal edges, vertices), the abundance of which increases with decreasing particle size.