Nanostructured α-Fe2O3 Thin Films for Photoelectrochemical Hydrogen Generation

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• 作者：Asif Ali Tahir ; K. G. Upul Wijayantha ; Sina Saremi-Yarahmadi ; Muhammad Mazhar ; Vickie McKee
• 刊名：Chemistry of Materials
• 出版年：2009
• 出版时间：August 25, 2009
• 年：2009
• 卷：21
• 期：16
• 页码：3763-3772
• 全文大小：959K
• 年卷期：v.21,no.16(August 25, 2009)
• ISSN：1520-5002

文摘

α-Fe₂O₃ thin film photoelectrodes were fabricated by aerosol-assisted chemical vapor deposition (AACVD) using a new hexanuclear iron precursor [Fe₆(PhCOO)₁₀(acac)₂(O)₂(OH)₂]·3C₇H₈ (1) (where PhCOO = benzoate and acac = 2,4-pentanedionate). The precursor (1) designed for AACVD has a low decomposition temperature and sufficient solubility in organic solvents and was synthesized by simple chemical techniques in high yield. It was characterized by melting point, FT-IR, X-ray crystallography, and thermogravimetry (TGA). The TGA analysis proved that complex (1) undergoes facile thermal decomposition at 475 °C to give iron oxide residue. In-house designed AACVD equipment was used to deposit highly crystalline thin films of α-Fe₂O₃ on fluorine-doped SnO₂ coated glass substrates at 475 °C in a single step. The material properties were characterized by XRD, XPS, and Raman spectroscopy, and the results confirmed that films were highly crystalline α-Fe₂O₃ and free from other phases of iron oxide. Further analysis of XRD data of the thin films proved the formation of crystalline hematite with an average diameter of 35 nm. X-ray photoelectron spectroscopy (XPS) confirmed that Fe is present only in the Fe³⁺ oxidation state. Scanning electron microscopy (SEM) showed that the needle-like particles having length in the range of 100 to 160 nm with a diameter of 30−50 nm are sintered together to form a compact structure of the 80-nm-thick α-Fe₂O₃ layer. Optical, electrical, and photoelectrochemical studies were conducted by UV−vis, electrochemical impedance spectroscopy, and steady-state current−voltage plots. The optical bandgap was estimated, and it is about 2.13 eV. The donor density of the α-Fe₂O₃ was 2.914 × 10²³ m⁻³, and the flatband potential is approximately −0.86 V vs V_Ag/AgCl. The photoelectrochemical characteristics recorded under AM 1.5 illumination indicated that the photocurrent density of 600 μA cm⁻² at 1.23 V vs RHE, which is among the highest reported for an undoped α-Fe₂O₃ photoelectrode to date.