Nanostructured α-Fe₂O₃ Thin Films for Photoelectrochemical Hydrogen Generation

Abstract

R-Fe 2 O 3 thin film photoelectrodes were fabricated by aerosol-assisted chemical vapor deposition (AACVD) using a new hexanuclear iron precursor [Fe 6 (PhCOO) 10 (acac) 2 (O) 2 (OH) 2 ] 3 3C 7 H 8 (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 R-Fe 2 O 3 on fluorinedoped SnO 2 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 R-Fe 2 O 3 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 Fe 3þ 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 R-Fe 2 O 3 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 R-Fe 2 O 3 was 2.914 Â10 23 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 R-Fe 2 O 3 photoelectrode to date.

Solar Water Splitting: Progress Using Hematite (α‐Fe2O3) Photoelectrodes

“…Typically, the capacitance is determined by fitting the frequency responses with a simple resistor-capacitor (RC) circuit model (see Figure 8 a). A single frequency, [30,50,56] multiple frequencies, [105] extrapolating to an infinite frequency, [54,57,126] or an entire range of high frequencies [65,[127][128] (for heavily doped samples) have been reported for both planar and structured electrodes. [24,[127][128] However since the classic MS relation relies on a simple parallel-plate capacitor model the application of EIS data from real systems has often been problematic.…”

Electrochemical deposition of Fe2O3 in the presence of organic additives: a route to enhanced photoactivity

“…Additionally, oxygen evolution catalysts 22,23 and passivation layers 24,25 are employed to decrease the overpotential of the multistep 4e À oxygen evolution reaction which is inherently sluggish on hematite photoelectrodes. Hematite photoanodes can be prepared following several strategies such as sol-gel methods, 26 spray pyrolysis 27,28 chemical vapour deposition (CVD) 15,29 sputtering, 19 atomic layer deposition (ALD) 30,31 and electrodeposition (ED). [32][33][34] ED presents numerous attractive features over the other techniques such as the use of non-toxic iron precursors, simple instrumentation, high exibility in terms of composition and experimental parameters, and easy scale up for the fabrication of large area electrodes.…”

Electrocatalytic activity of CoFe2O4 thin films prepared by AACVD towards the oxygen evolution reaction in alkaline media

“…Various Co containing compounds, such as, oxides [9][10][11], phosphates [12,13], perovskites [14], and (oxy)hydroxides [15] have shown good OER activity. Fe is another abundant element; whilst iron oxide (α-Fe 2 O 3 ) has been extensively studied for photoelectrochemical water oxidation [16], comparatively little work has been carried out on its use as an OER electrocatalyst in an alkaline media [17]. It has been generally established that transition metal oxides often form (oxy)hydroxides at their surfaces in alkaline conditions.…”