Photoanodic response of hematite electrode to citric acid in aqueous solution
Introduction
Iron oxide such as hematite with merits of abundance, harmlessness and stability is expected to be utilized as photo-functional material acting under visible light irradiation. There are several reports concerning photoelectrochemical characteristics of iron oxide [1], [2], [3], [4], [5], [6], [7], photooxidation of water [8], [9], [10], [11], [12], [13], [14], [15] and photocatalytic water purification [16], [17], [18], [19], [20], [21] by using iron oxide. We have studied the behavior of iron oxide photoelectrode in aqueous solution for the purpose of conversion of visible light energy to chemical and electric energy. In order to use iron oxide as a photo-functional electrode effectively, it is necessary to make clear its photoanodic response to chemical species. We have already reported the photoanodic deposition of PbO2 from Pb2 + on iron oxide electrode in aqueous solution [22] and also the behavior of iron oxide/polyaniline photoelectrode [23] under visible light. As predicted from our result of the occurrence of photoanodic reaction of Pb2 + ions with more positive oxidation potential than that of H2O, the hole generated in the valence band of iron oxide due to absorption of visible light may have high oxidation ability for chemical species in the solution. Understanding of photoanodic oxidation of organic materials on hematite under visible light irradiation will be important in a new development of synthetic method for organic materials based on light energy conversion.
In the present work, we carried out the electrochemical preparation of iron oxide film on the titanium substrate in aqueous solution containing Fe2 + ions and examined its response to citric acid in order to get knowledge of the photoanodic process of organic acids on the iron oxide in aqueous solution. We used the current pulse method as a preparation technique of iron oxide because a homogeneous film deposition could be expected by this method.
Section snippets
Experimental
An iron oxide film (geometric surface area of 1.0 cm2) was prepared on a titanium substrate by current pulse deposition with repetition of cathodic pulse (current: Ic, time: 1 s) and anodic pulse (current: Ia, time: 1 s) as shown in Fig. 1. Before electrolysis, the titanium plate (Nilaco, size: 30 × 20 × 0.2 mm) was treated as follows. The surface was polished with alumina powder (BAIKOWSKI, Baikalox 0.3CR), washed with pure water and cleaned ultrasonically. Then, the titanium was immersed in 6 M
Characterization of the iron oxide film
Fig. 2 shows the potential of titanium working electrode during the electrolysis by repetition of cathodic pulse (Ic = − 7 mA) and anodic pulse (Ia = + 1 mA) in aqueous 10 mM FeCl2–0.15 M NaCl solution under O2 bubbling for 100 s. The potential changed periodically with the cathodic and anodic current pulses. In the case of galvanostatic deposition with the current of − 7 mA for 50 s in the same solution as above, the potential of working electrode became almost constant value of − 1.60 V vs. Ag/AgCl.
Fig. 3a
Conclusion
We prepared the hematite film by current pules deposition and heat treatment in air. The more homogeneous film was obtained by the current pulse method (Ic = − 7 mA, Ia = + 1 mA, time: 100 s) compared with the galvanostatic reduction (current: − 7 mA, time: 50 s) in the presence of O2. The as-deposited film by the current pulse method had the structure of FeO and Fe3O4. The Fe3O4 structure did not appear on the as-deposited film by the galvanostatic reduction. The formation of Fe3O4 due to anodic pulse may
Acknowledgement
This work has been supported by the Grant-in-Aid for Scientific Research (C) No. 24550174 of Japan Society for the Promotion of Science (JSPS) from 2012 to 2014.
References (28)
- et al.
The influence of different electrodeposition E/t programs on the photoelectrochemical properties of α-Fe2O3 thin films
Thin Solid Films
(2010) - et al.
Influence of potential, deposition time and annealing temperature on photoelectrochemical properties of electrodeposited iron oxide thin films
J. Alloys Compd.
(2012) - et al.
Production of hydrogen and oxygen by water splitting using laser induced photo-catalysis over Fe2O3
Appl. Catal. A Gen.
(2004) - et al.
Microwave-assisted low temperature fabrication of nanostructured α-Fe2O3 electrodes for solar-driven hydrogen generation
Int. J. Hydrog. Energy
(2010) - et al.
On the improvement of PEC activity of hematite thin films deposited by high-power pulsed magnetron sputtering method
Appl. Catal. B Environ.
(2015) - et al.
Preparation of iron oxide thin film by metal organic deposition from Fe (III)-acetylacetonate: a study of photocatalytic properties
Thin Solid Films
(2000) - et al.
2. Sensitized degradation of chlorophenols on iron oxides induced by visible light comparison with titanium oxide
Appl. Catal. B Environ.
(2001) - et al.
Preparation, characterization and photocatalytic activity of ZnO, Fe2O3 and ZnFe2O4
J. Photochem. Photobiol. A Chem.
(2002) - et al.
Visible light photocatalytic decomposition of 2-naphthol by anodic-biased α-Fe2O3 film
J. Colloid Interface Sci.
(2006) - et al.
Self-assembled hematite (α-Fe2O3) nanotube arrays for photoelectrocatalytic degradation of azo dye under simulated solar light irradiation
Appl. Catal. B Environ.
(2010)
Photoanodic response of iron oxide electrode in aqueous solution and its application to Pb2 + removal under visible light irradiation
Electrochim. Acta
Chemical reactions of electrons and holes at the ZnO/electrolyte-solution interface
Electrochim. Acta
The different photoelectrochemical behavior of sintered and flame-oxidized Fe2O3
J. Electrochem. Soc.
Open-circuit photopotentials and photoelectrochemical behavior of the Si-doped α-Fe2O3 semiconductor electrode in acetonitrile solutions
J. Electrochem. Soc.
Cited by (1)
Influence Mechanism of the Iron-Rich Raw Material on the Iron-Based Crystalline Glazes
2022, Guang Pu Xue Yu Guang Pu Fen Xi/Spectroscopy and Spectral Analysis