Pulsed Laser Deposited Fe₂TiO₅ Photoanodes for Photoelectrochemical Water Oxidation

Abstract

Pulsed laser deposition (PLD) is an appealing technique to fabricate thin films with specific film orientation, stoichiometry, and morphology through tuning of experimental parameters. Here, we present Fe2TiO5, one of the promising photoanode materials, grown on fluorine-doped tin oxide (FTO) substrates through PLD. The structural and morphological properties of Fe 2 TiO 5 films, grown at room temperature and under varying oxygen pressure were studied. After deposition, all films were annealed in air at 650°C for 2 hours to complete phase crystallization. Films grown under vacuum (1.1 x 10 -6 mbar) were compact, dense, and had the anticipated stoichiometry, but lacked the long-range order expected for a crystalline phase in Xray diffraction. In contrast, using an oxygen pressure (p O 2 ) of around 9.7 x 10 -2 mbar during growth resulted in nanoporous, crystalline, and near-stoichiometric films of the orthorhombic Fe 2 TiO 5 pseudobrookite phase. These films demonstrated a photocurrent density of around 0.16 mA/cm 2 at 1.23 V vs RHE and a negative shift in onset potential by 150 mV under backside illumination as compared to the films grown under vacuum. Notably, these films exhibited a preferred (101) orientation of the pseudobrookite grains.This study proposes a viable strategy to fabricate pure phase and anisotropic Fe 2 TiO 5 photoanodes on FTO through PLD. This will pave a way to synthesis of other complex metal oxide photoelectrodes with precise control over critical properties like crystallinity, stoichiometry, and porosity that is imperative for their application in solar energy conversion.

Experimental and computational study on the influence of cobalt substitution on the structural, impedance, electronic, magnetic, and optical properties of pseudobrookite-structured Fe2TiO5

“…Their bandgap values of oxygen-deficient thin films are 2.18 eV (direct gap) and 2.04 eV (indirect gap). 46 If one compares the values of the bandgaps in the current study with those required for good photocatalysis, one finds that these values remain well within the range of the optimum bandgap of 1.6–2 eV, as pointed out by Bassi et al 46 Of significant note are the defect states in the minority channel of the Co-substituted sample (Fig. 9(d)), which decrease the bandgap significantly from that of the majority channel.…”

Highly Efficient Surface Charge Transfer in Fe2TiO5 Epitaxial Thin Film Photoanodes

“…In contrast, Fe 2 TiO 5 , the mineral known as pseudobrookite with a band gap of 2.18 eV, does not have this issue due to its stoichiometry hosting the most stable oxidation states for both cations. Recently, this material has been incorporated in polycrystalline heterostructures, such as Fe 2 TiO 5 /α-Fe 2 O 3 or Fe 2 TiO 5 /TiO 2 nanostructures, and has been shown to greatly enhance the photoanodic performance. − Several explanations have been proposed, such as favorable band edge positioning for bulk charge separation and reduced surface recombination; nevertheless, the nanostructured nature of the photoanodes, for example, with multiple crystal facets and variation in the size of each nanostructure, have limited the characterization of the intrinsic PEC properties. This calls for a well-defined surface to elucidate the underlying surface reaction mechanisms. − Epitaxial thin films with well-defined crystalline orientation, surface flatness, surface area, and film thickness are ideal for such studies and serve as a solid platform for developing high-performance photoelectrodes, minimizing the effects from high-density grain boundaries or local off-stoichiometry commonly present in polycrystalline samples …”

Zn-Doped Fe2TiO5 Pseudobrookite-Based Photoanodes Grown by Aerosol-Assisted Chemical Vapor Deposition

“…Very recently, Bassi et al . also reported for the first time Fe 2 TiO 5 photoanodes grown by pulsed laser deposition . Lee et al .…”

“…10 Very recently, Bassi et al also reported for the first time Fe2TiO5 photoanodes grown by pulsed laser deposition. 12 Lee et al reported a novel electrochemical method based on the use of metal-catechol complexes for the fabrication of pure Fe2TiO5 photoanodes. 13 Kuang et al reported an electrospray technique for the preparation of Fe2TiO5 photoanodes and posteriorly modified them by surface state passivation with Al 3+ and by FeOOH decoration, showing both approaches were effective in increasing the resulting photocurrent density values to 0.52 mA cm -2 at +1.23 VRHE.…”