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.