Influence of anodization time on the surface modifications on alpha-Fe2O3 photoanode upon anodization

In searching for a suitable semiconductor material for hydrogen production via photoelectrochemical water splitting, alpha-Fe2O3 received significant attention as a promising photoanode due to its band gap (similar to 2.1 eV), good stability, low cost, and natural occurrence alpha-Fe2O3 thin films were prepared by economic and facile dip coating method and subsequently subjected to an anodic potential of 700 mV versus Ag/AgCl in 1M KOH for different anodization times (1, 10, and 900 min) under illumination. X-ray diffractometry revealed increase in crystallites size from similar to 31 nm for nanoparticles in pristine state to similar to 38 and 44 nm after anodization for 1 and 900 min, respectively. A clear positive correlation between anodization time and grain (particle) size was observed from field emission gun scanning electron microscopy and atomic force microscopy (AFM); longer exposure time to anodizing conditions resulted in larger grains. Grain size increased from similar to 57.9 nm in pristine state to similar to 153.5 nm after anodization for 900 min. A significant smoothening of the surface with increase in anodization time was evident from AFM analysis.