Columnar Fe2O3 arrays via plasma-enhanced growth: Interplay of fluorine substitution and photoelectrochemical properties

• Novel PE-CVD approach to β-Fe2O3 nanomaterials on ITO substrates.
• Fabrication of columnar arrays with an homogeneous in-depth fluorine doping.
• First example of β-Fe2O3 application in photoelectrochemical water splitting.
• Modulation of optical and photoelectrochemical properties as a function of fluorine content.

A single-step plasma enhanced-chemical vapor deposition (PE-CVD) route for the synthesis of F-doped iron(III) oxide nanomaterials is presented. Growth experiments, performed from a fluorinated Fe(II) β-diketonate precursor on Indium Tin Oxide (ITO) between 200 and 400 °C, yielded columnar β-Fe2O3 arrays with a preferential (100) growth direction. The fluorine content in the deposits could be adjusted by the sole variation of the deposition temperature controlling, in turn, the optical absorption and energy bandgap. Photocurrent measurements and Mott–Schottky analyses, carried out in Na2SO4 solution under one sun illumination, evidenced a conductivity switch from n- to p-type upon increasing fluorine amount in the obtained nanomaterials. The sample photocurrent density, donor content and flatband potential support the hypothesis that a progressive substitution of oxygen by fluorine in the iron(III) oxide lattice can alter electronic structure and extend charge carrier lifetimes, making anion-doped β-Fe2O3 an efficient water oxidation catalyst.