Synthesis and Characterization of Layered Double Hydroxides/Nafion Composites for Fuel Cell Application
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Synthesis and Characterization of Layered Double Hydroxides/Nafion Composites for Fuel Cell Application Inga Elkina, Bolnale Abayomi, Miriam Harewood, Sheriff Abudu, Elizabeth Williams, Raymond Butcher, and Dharmaraj Raghavan Department of Chemistry, Howard University, 525 College Street, Washington, DC, 20059
ABSTRACT In this study, magnesium-aluminum (Mg-Al) based LDHs with different Mg2+/Al3+ ratios were prepared by co-precipitation method and modified with perfluorooctane-sulfonic acid tetraethylammonium salt (PFOSA). X-Ray Diffraction (XRD), Atomic Force Microscopy (AFM), Fourier Transfer Infrared spectroscopy (FTIR) and Thermogravimetric Analysis (TGA) were carried out to obtain the structural and thermal characteristics of resulting materials. The organo-modified LDHs have been used in the formulation of Nafion® nanocomposites. Nanocomposite membranes were prepared by casting of LDH/PFOSA nanoparticles dispersed in Nafion® solution. Then, modified LDH/Nafion composite membranes were evaluated for water retention capability at ambient and elevated temperature. INTRODUCTION Sulfonated perfluorocarbon polymers such as Nafion®, currently used as proton-exchange membrane (PEM), exhibit unacceptably poor performance at high temperature and in low humidity conditions. This limits their application as proton conducting polymer electrolyte membranes in fuel cell. To overcome these and other weaknesses of Nafion® and similar materials, the development of nanocomposite membranes on the basis of lamellar structure of synthetic clay was proposed. Due to layered structure and capability to intercalate a variety of organic species between their layers, these types of materials are excellent candidates for creation of a new class of proton conducting membranes. Furthermore, nanostructured materials based on Layer Double Hydroxides (LDHs) are very attractive for preparation of polymer nanocomposite membranes for fuel cell application due to their excellent mechanical and thermal properties, and rich chemistry. EXPERIMENTS In this study, magnesium-aluminum (Mg-Al) based LDHs with different Mg2+/Al3+ ratios were prepared by co-precipitation method [1,2] and modified with perfluorooctane-sulfonic acid tetraethylammonium salt (PFOSA). The PFOSA/LDH was dispersed in Nafion solution using sonifier. Nanocomposite membrane was formed by casting the solution on a glass slide.
RESULTS AND DISCUSSION
OH
CF2 SO3
4000
OH
3000
2000
Figure 1. FTIR data for LDH and LDH-PFOSA with Mg/Al ratio 3:1.
CO3
M-OH 948
H2O
1622
Mg0.75Al0.25(OH)2(CO3)0.125
1369
3522
1057
Mg0.75Al0.25(OH)2(C8F17SO3)0.25 H2O
1633
A
1156
3552
Complete characterization of the PFOSA modified LDH was accomplished using the conventional FTIR, XRD and TGA techniques. FTIR analysis confirmed the presence of representative chemical groups in the structure of initial and modified LDH (figure 1). According to the TGA analysis, the decomposition temperature of modified LDH/PFOSA compounds is in the range of 460- 480oC, which is significantly hi
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