Nanostructured α-Fe2O3 Electrodes for Solar Driven Water Splitting: Effect of Doping Agents on Preparation and Performance

Si-doped nanostructured hematite alpha-Fe2O3 has attracted significant attention as a low-cost, high-efficiency candidate material for photoelectrochertrical water splitting. In this work, we investigated the effect of Si incorporation on the preparation and performance of alpha-Fe2O3 films produced by atmospheric pressure chemical vapor deposition (APCVD). Structural, optical, electrical, and photoelectrochemical characterization of doped and undoped hematite films was performed using XRD, FIB/SEM, Raman spectroscopy, UV-vis absorption spectroscopy, J-V and electrochemical capacitance measurements. It was concluded from the XPS data that Si is incorporated in the hematite structure as Si4+. The results suggest that Si-free additives as well as the use of fluorinated transparent conducting oxide (FTO) substrates can influence the preferred orientation of hematite films. It was also found that the incorporation of silicon at very low levels led to the formation of disorder in the hematite structure. Moreover, it is shown that the optical bandgap of Si-doped film increased with the increase of TEOS flow rate. It contributed to the reduction in the size of the hematite nanoparticles and the size quantization effect. The observed donor densities for the doped samples seemed to be much higher than the true values, mainly because the total capacitance measured was higher than space charge layer capacitance, which resulted from the surface area enhancement in the doped films. Therefore, it is considered that donor densities of doped films were smaller than that of the undoped hematite films.