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

Abstract

Si-doped nanostructured hematite (α-Fe2O3) has attracted significant attention as a low-cost, high-efficiency candidate material for photoelectrochemical water splitting. In this work, we investigated the effect of Si incorporation on the preparation and performance of α-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.

Solar Water Splitting: Progress Using Hematite (α‐Fe2O3) Photoelectrodes

“…[69,113] In continuing work with this deposition technique ferrocene and tetramethyl orthosilicate (TMOS) were found to be viable sources of iron and silicon, respectively. [117][118] The use of ferrocene is notable for replacing the toxic iron pentacarbonyl, however the photocurrent density obtained remained less than 1 mA cm…”

How Should Iron and Titanium be Combined in Oxides to Improve Photoelectrochemical Properties?

“…21 For example, ferric doping of TiO 2 lowers the bandgap from 3.2 to 1.9 eV, depending on the Fe content and the synthesis procedure. 22,23 However, high doping levels often lead to heterogeneous materials.…”

The influence of Ti- and Si-doping on the structure, morphology and photo-response properties of α-Fe2O3 for efficient water-splitting: Insights from experiment and first-principles calculations

“…Fig. 2) may be indicative of the presence of mainly substitutionally-doped Si in the hematite coating as a Si 4+ species [3,30,31]. Conversely, the peak at ~99 eV indicates a certain amount, albeit relatively small, of the elemental form of Si dopant present in the hematite film.…”