Electrodeposited nanostructured α-Fe₂O₃ photoanodes for solar water splitting: Effect of surface co-modification on photoelectrochemical performance

Photoelectrochemical response of electrodeposited hematite (α-Fe ₂O₃) thin films, whose surface has been modified by a catalytic cobalt layer, has been studied. Structural and morphological characteristics of the resulting nanostructured hematite films have been studied by X-ray diffraction and scanning electron microscopy techniques. Surface characterization of the Co-modified hematite films has been carried out by X-ray photoelectron spectroscopy in order to study the chemical nature of Co onto these films. The hematite films exhibited an n-type behavior, and a donor carrier concentration, N_D 3 ×10¹⁷ and 10 ¹⁸ cm^-3 for the un-modified and Co-modified ones, respectively. The photoelectrochemical performance of the un-modified and Co-modified electrochemically grown hematite thin films has been explored using a liquid-junction in a photoelectrochemical system in a 0.1 M NaOH electrolytic solution, under monochromatic illumination of wavelengths over the range 350-600 nm. Significant performance gaining can be seen upon Co-modification throughout the illumination wavelengths. Cobalt modification enhances the IPCE by a factor of 1.1-2.0 (370-450 nm range), and by a factor of 2.0 (at 350 nm). With an IPCE of 46 at 370 nm at 1.43 V vs. RHE, this electrode is much more efficient in water photo-oxidation than the best published Fe₂O₃ single-crystal specimen.