Influence of anodization time on the surface modifications on [alpha]-Fe sub(2)O sub(3) photoanode upon anodization

In searching for a suitable semiconductor material for hydrogen production via photoelectrochemical water splitting, [alpha]-Fe sub(2)O sub(3) received significant attention as a promising photoanode due to its band gap (~2.1 eV), good stability, low cost, and natural occurrence. [alpha]-Fe sub(2)O sub(3) 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 ~31 nm for nanoparticles in pristine state 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 ~57.9 nm in pristine state 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.