Morphology and crystal structure control of α-Fe₂O₃ films by hydrothermal-electrochemical deposition in the presence of Ce³⁺ and/or acetate, F⁻ ions

Abstract

Hydrothermal-electrochemical growth of Hematite (a-Fe 2 O 3 ) thin films in the presence of Ce 3+ and/or CH 3 COO À and F À ions is reported. Primary attention is paid to understanding the synergistic effect of temperature and additive ions on the growth of Hematite particles. The literature describes the shapecontrolled electrodeposition of iron oxide films, but these reports involve low-temperature depositions (<100 C) that require a post-annealing step to obtain the Hematite phase. We studied size and shape control of Hematite crystals by introducing capping agents during hydrothermal-electrochemical deposition (HED) at 130 C under autonomous pressure. When HED is used together with growthmodifying species such as CH 3 COO À and/or Ce 3+ , Hematite thin films with various structures including spherical, rhombohedral and platelet-like particles were obtained which were crystallized directly in the a-Fe 2 O 3 phase without thermal annealing. In contrast, either Lepidocrocite or an amorphous phase forms with low-temperature electrodeposition under otherwise identical conditions. Addition of F À into the deposition solution induces formation of bundles that are composed of square planar Akaganeite particles even during HED. The aspect ratio of the Akaganeite particles is controlled with co-addition of Ce 3+ ions. This variety of nanostructures gives us the opportunity to evaluate the photoelectrochemical performance of the a-Fe 2 O 3 films based on particle size and shape. It was demonstrated that porous, square planar a-Fe 2 O 3 with a high aspect ratio shows the highest performance.

Photoactive Heterostructures Based on α-Fe2O3 and CuO Thin Films for the Removal of Pollutants from Aqueous Solutions

“…Besides, the heterostructure morphology was slightly different from bare Fe 2 O 3 and ZnO thin films. The variation of the morphologies for the thin films could be related to the lattice structure and defects produced during the deposition of films and the subsequent nucleation and growth [39]. Besides, the cross-section image of Fe 2 O 3 /ZnO film shown in Figure 2b reveals that the thickness obtained was about 2.04 μm.…”

<p>Preface</p>

“…It can absorb light in the visible region due to its bandgap of ~2.0 eV and promises a maximum theoretical photocurrent and solar-to-hydrogen (STH) efficiency of ~14 mA/cm 2 and ~17%, respectively (Dias et al 2014;Murphy et al 2006). In addition, α-Fe 2 O 3 is the most common crystal structure of the oxides of iron, and it is easy to process (Yilmaz and Unal 2016). However, the efficiency of α-Fe 2 O 3 is yet to attain the theoretically predicted value due to its poor conductivity, high electron-hole recombination, inefficient charge separation (Lee et al 2014;Xi and Lange 2018), high overpotential, and low absorption coefficient, requiring films with a thickness of over 400 nm for sufficient photon utilization (Sivula et al 2011).…”

Hydrothermal–electrochemical growth of heterogeneous ZnO: Co films

“…HED primarily affects the growth kinetics; hence, crystallinity and morphology of deposited particles (Yilmaz and Unal 2015). Furthermore, by the synergistic effect of the growth-modifier molecules and HED, metal oxide particles with various shapes including spherical-, rhombohedral-, and platelet-like particles can be obtained (Yilmaz and Unal 2013;Yilmaz and Unal 2016;Yilmaz and Unal 2014). Effect of additives is significantly influenced by high-temperature electrodeposition with each cation and anion behaving differently.…”