Fabrication of a Microtubular La0.6Sr0.4Ti0.2Fe0.8O3−δ Membrane by Electrophoretic Deposition for Hydrogen Production

Hindawi Publishing Corporation Advances in Materials Science and Engineering Volume 2015, Article ID 505989, 6 pages http://dx.doi.org/10.1155/2015/505989 Research Article Fabrication of a Microtubular La0.6Sr0.4Ti0.2Fe0.8O3−𝛿 Membrane by Electrophoretic Deposition for Hydrogen Production Kyoung-Jin Lee, Yeong-Ju Choe, Jun-Sung Lee, and Hae-Jin Hwang Department of Materials Science and Engineering, Inha University, 253 Yonghyun-dong, Nam-gu, Incheon 402-751, Republic of Korea Correspondence should be addressed to Hae-Jin Hwang; Received 30 November 2014; Revised 25 March 2015; Accepted 6 April 2015 Academic Editor: Simo-Pekka Hannula Copyright © 2015 Kyoung-Jin Lee et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Microtubular type La0.6 Sr0.4 Ti0.2 Fe0.8 O3−𝛿 (LSTF) membranes were prepared by electrophoretic deposition (EPD). The oxygen permeation and hydrogen production behavior of the membranes were investigated under various conditions. LSTF green layer was successfully coated onto a carbon rod and, after heat treatment at 1400∘ C in air, a dense LSTF tubular membrane with a thickness of 250 mm can be obtained. The oxygen permeation and hydrogen production rate were enhanced by CH4 in the permeate side, and the hydrogen production rate by water splitting was 0.22 mL/min⋅cm2 at 1000∘ C. It is believed that hydrogen production via water splitting using these tubular LSTF membranes is possible. 1. Introduction Hydrogen is considered to be a next generation clean and efficient fuel that can be used in electrochemical devices, such as fuel cells or internal combustion engines, to power vehicles or generate electricity. Hydrogen is normally produced by methane steam reforming (CH4 + 2H2 O = 3H2 + CO) or the electrolysis of water because pure hydrogen does not occur naturally on Earth in large quantities. However, the methane steam reforming releases carbon dioxide into the atmosphere and does not help to decrease greenhouse gases. In addition, the electrolysis of water requires large amounts of electricity to decompose water and produce hydrogen. Hydrogen production by high temperature water splitting (H2 O ⇔ H2 + 1/2O2 ) is one of the most important long-term goals in hydrogen fuel production [1, 2]. Since the equilibrium constant of the water splitting reaction is very small, it generates very low concentrations of hydrogen and oxygen, even at high temperatures (0.1% hydrogen and 0.042% oxygen at 1600∘ C). This limitation of water dissociation can be overcome by controlling the thermodynamic equilibrium. If the produced oxygen or hydrogen can be removed from the reactor, the equilibrium is shifted towards the dissociation of water, thereby increasing the hydrogen production rate up to a realistic level. Putting this in mind, water splitting via an oxygen transport membrane (OTM) is one of the most promising routes for sustainable hydrogen production without releasing carbon dioxide. Dissociated oxygen can be selectively transported outside the reactor through the OTM, and the hydrogen production rate depends on the rate at which oxygen is removed from the reactor. Therefore, an OTM with high oxygen permeability (i.e., excellent mixed ionic and electronic conductivity and good oxygen surface exchange kinetics [3, 4]) is required. Perovskite-type oxides have been widely used as oxygen transport membrane materials because of their high oxygen permeability and good durability at high temperatures (both in oxidized and reduced atmospheres). Strontium and cobalt codoped barium ferrite (BSCF) are the most common materials for OTMs. Although BSCF shows excellent oxygen ionic and electronic transport properties, it suffers from a large thermal expansion coefficient and long-term structural and electrochemical instability, especially in atmospheres containing carbon dioxide. Alternatively, lanthanum and iron codoped strontium titanate (La1−𝑥 Sr𝑥 Ti1−𝑦 Fe𝑦 O3−𝛿 (LSTF)) has been developed as an OTM material by some researchers. Unlike cobalt, which exists at the B site of the perovskite ABO3 , titanium is less likely to undergo valence changes and provides a more 2 Advances in Materials Science and Engineering LSTF suspension Graphite Graphite -Bottom- -Top- Power source LSTF powder Nickel mesh Hole LSTF LSTF LSTF ⟨Sintering (eliminate graphite)⟩ ⟨Layer electrophoretic deposition⟩ (a) (b) Figure 1: Schematic diagram of the (a) EPD process and (b) sintering process. stable crystal structure in a reducing atmosphere. The substitution of Fe by Ti is expected to improve durability and to lower the cost of materials. In addition, titanium-doped perovskite materials have been reported to catalyze the methane reforming reaction [5]. In this study, a dense microtubular La0.6 Sr0.4 Ti0.2 Fe0.8 O3−𝛿 (LSTF) membrane was fabricated by electrophoretic deposition (EPD). The microstructure and oxygen permeation behavior of this material were investigated. 2. Experimental Procedure 2.1. Preparation of a Microtubular Membrane by EPD. LSTF powders were synthesized from La2 O3 (99.9%, YAKURI, Japan), SrCO3 (99.9%, Sigma Aldrich, USA), TiO2 (99.9%, High Purity Chemicals, Japan), and Fe2 O3 (99.9%, High Purity Chemicals, Japan) by a solid state reaction technique. The starting materials were mixed using a planetary ball mill and then calcined at 1000∘ C for 5 h. Microtubular LSTF membranes were fabricated using a sealless tube design by electrophoretic deposition (EPD), as shown in Figure 1(a). EPD is a colloidal deposition technique that has been proven to be simple and inexpensive for the production of many advanced ceramics bodies. EPD is recognized for its great potential to economically fabricate thin, dense, and gas-tight electrolytes, as well as porous electrodes for solid oxide fuel cell applications [6]. First, the LSTF powder was dispersed in acetyl acetone. After 15 min of ultrasonication, a stable slurry can be obtained. The LSTF slurry was stable for at least for 24 h. A graphite rod (10 mm in diameter and 50 mm in length), which was used as the substrate, was immersed in the LSTF slurry and 100 V of DC voltage was applied between the graphite rod and the nickel counter electrode for 10 min. The distance between the graphite rod and counter electrode was 13 mm. After the EPD process, a thin LSCF green layer was homogenously formed on the graphite rod. The dipcoating process was conducted using the same LSTF slurry to improve the strength of the membrane. The graphite tube, coated by the LFTF green layer, was finally fired at 1400∘ C for 2 h in air to remove the graphite substrate and sinter the LSCF green body. The active surface area of the microtubular membrane was 1.85 cm2 . 2.2. Characterization. The crystal structure of the microtubular LSTF membranes was analyzed by X-ray diffraction (XRD, RU- (...truncated)