Amorphous TiO2 was deposited on the photoanodes by atomic layer deposition (ALD) technique (R200, Picosun). Tetrakis(dimethylamino)titanium (TDMAT, 99.99%, Aldrich) and H2O were used as precursors for Ti and O, respectively. Each photoanode was placed in ALD chamber at 120°C, TDMAT heated at 85°C was put with a 1.6s pulse, followed by N2 purge with a 6.0 s. H2O was kept at room temperature with a 0.1 s pulse, followed by a 6.0 s N2 purge.