Photo-electrochemical (PEC) water splitting of hematite photoanodes suffers from low performance and efficiency. One way to increase the performance is to increase the electrochemically active surface area available for the oxygen evolution reaction. In this study, we use high ion flux, low energy helium plasma exposure to nanostructure sputtered iron thin films. Subsequent annealing in air at 645 °C leads to the formation of PEC active hematite (α-Fe₂O₃) phase in these films. The surface area, as derived from electrochemical impedance spectroscopy (EIS), was seen to increase 10–40 times with plasma exposure. The photocurrent density increased by 2–5 times for the plasma exposed films as compared to the unexposed films. However, the less nanostructured film showed a higher photocurrent density. These findings were explained by detailed chemical and structural characterization in combination with electrochemical characterization and attributed to the presence of secondary elements in the film as well as to the presence of secondary iron oxide phases apart from hematite. This work demonstrates the complex effect of plasma exposure on both film morphology and chemical composition of PEC thin films and provides further understanding on how this technique can be used for nanostructuring of other functional films.

赤铁矿光阳极的光电化学（PEC）分解水性能和效率低。一种提高性能的方法是增加可用于氧释放反应的电化学活性表面积。在这项研究中，我们使用高离子通量，低能氦等离子体暴露于纳米结构溅射铁薄膜。随后的退火在空气中在645℃通入PEC活性赤铁矿的形成（的α-Fe ₂ ö ₃）相中的这些影片。由电化学阻抗谱（EIS）得出的表面积随着等离子体暴露而增加了10–40倍。与未曝光的胶片相比，等离子曝光的胶片的光电流密度提高了2到5倍。然而，较少纳米结构的膜显示出较高的光电流密度。这些发现可以通过详细的化学和结构表征与电化学表征相结合来解释，并且归因于薄膜中存在次要元素以及除赤铁矿之外还存在次要氧化铁相。