Mesoporous α-Fe2O3 thin films synthesized via the sol–gel process for light-driven water oxidation

Abstract

This work reports a facile and cost-effective method for synthesizing photoactive α-Fe(2)O(3) films as well as their performances when used as photoanodes for water oxidation. Transparent α-Fe(2)O(3) mesoporous films were fabricated by template-directed sol-gel chemistry coupled with the dip-coating approach, followed by annealing at various temperatures from 350 °C to 750 °C in air. α-Fe(2)O(3) films were characterized by X-ray diffraction, XPS, FE-SEM and electrochemical measurements. The photoelectrochemical performance of α-Fe(2)O(3) photoanodes was characterized and optimized through the deposition of Co-based co-catalysts via different methods (impregnation, electro-deposition and photo-electro-deposition). Interestingly, the resulting hematite films heat-treated at relatively low temperature (500 °C), and therefore devoid of any extrinsic dopant, achieve light-driven water oxidation under near-to-neutral (pH = 8) aqueous conditions after decoration with a Co catalyst. The onset potential is 0.75 V vs. the reversible hydrogen electrode (RHE), thus corresponding to 450 mV light-induced underpotential, although modest photocurrent density values (40 μA cm(-2)) are obtained below 1.23 V vs. RHE. These new materials with a very large interfacial area in contact with the electrolyte and allowing for a high loading of water oxidation catalysts open new avenues for the optimization of photo-electrochemical water splitting.

Photoelectrocatalytic oxidation of Rhodamine B with sprayed <I>α</I>-Fe<SUB>2</SUB>O<SUB>3</SUB> photocatalyst

“…All films show wide absorption band edge upto 600 nm which is in agreement with result obtained by Hamd et al28 In optical absorption of compounds containing Fe 3+ cations have three types of electronic transitions are present i.e., Delivered by Publishing Technology to: University of North Carolina/ACQ Services IP: 170.164.50.90 On: Mon, 12 Oct 2015 02:SEM micrographs of Fe 2 O 3 thin films for various deposition temperatures. (i) ligand to metal charge-transfer transitions, (ii) Fe 3+ ligand field transition or the d-d transitions, and (iii) pair excitations resulting from the simultaneous excitations of two neighboring Fe 3+ cations that are magnetically coupled.…”

Combining Mesoporosity and Ti-Doping in Hematite Films for Water Splitting

“…The best values are currently around 3 mA/cm 2 (at 1.23 V vs reference hydrogen electrode) 5, 10 for nanostructured films with an additional dopant to improve conductivity and a catalyst to reduce the overpotential. [4][5][11][12][13][14][15][16][17][18] Nanostructuration of the photoanode is used as a strategy to address the short diffusion length of holes in hematite by reducing the distance that photogenerated holes have to travel to reach the electrolyte. [4][5] 4 Nanostructuration of the hematite photoanode can be achieved by various methods, such as colloidal solution deposition [19][20][21][22] , electrochemical deposition [23][24][25][26] , spray pyrolysis 11, 27-28 , hydrothermal synthesis 13,[29][30] , atmospheric pressure chemical vapor deposition 5,31 or copolymerbased soft templating.…”

New Fe2TiO5-based nanoheterostructured mesoporous photoanodes with improved visible light photoresponses

“…20 Zhang et al also observed that Fe 2 O 3 /TiO 2 heterostructures with high Fe contents (24 wt%) deposited by chemical vapor deposition on activated carbon bers allowed interesting photo-catalytic activities for the degradation of methyl orange. 36,37 Compared to other chemical approaches, 20,33 the sol-gel process allows a very good control of the lm microstructure through careful tuning of the sol composition, the heat treatment and the deposition conditions. [23][24][25] These results highlight the need for improving the morphology and the electronic structure of TiO 2 to tune separation and transportation of photo-excited charge carriers.…”