Fuel Cell Membranes Based on Polymer-Modified Silica Colloidal Crystals and Glasses: Proton Conductivity and Fuel Cell P
- PDF / 1,962,529 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 53 Downloads / 227 Views
Fuel Cell Membranes Based on Polymer-Modified Silica Colloidal Crystals and Glasses: Proton Conductivity and Fuel Cell Performance Amir Khabibullin and Ilya Zharov Department of Chemistry, University of Utah, Salt Lake City, UT 84112, USA ABSTRACT We describe a hybrid organic-inorganic fuel cell membrane material based on silica colloidal crystal and using EEMA/SPM co-polymers. We demonstrate that there is an S-shaped dependence of proton conductivity on the amount of sulfonyl groups in the copolymer for the copolymer-modified membranes and that there is no significant increase in proton conductivity with increasing amount of sulfonated monomer content above 60%. The studies of fuel cell potential dependence on the degree of sulfonation show that the presence of non-ionic moieties improves the performance of fuel cell, likely due to the reduction of methanol cross-over through the membrane. The fuel cells using the polymer-modified silica colloidal membranes perform better than Nafion 117. INTRODUCTION Fuel cells attract much attention as promising energy conversion technology that is environmentally friendly. [1] A proton conductive membrane is one of the most important parts of the fuel cell. [2] Polymer electrolyte membranes (PEM) are most commonly used for creating proton conductive membranes. [3] In addition to having suitable proton conductivity, it is also crucial for a fuel cell membrane to be non-swelling upon exposure to methanol and water, to be mechanically and thermally stable and to remain hydrated at elevated temperatures. [4,5] Hybrid organic-inorganic materials may meet all these requirements. [6-8] Recently, we reported the development of such hybrid systems, where a rigid highly ordered silica colloidal crystal containing a continuous network of nanopores provides mechanical and thermal stability, non-swelling and water retaining properties, while polymer brushes grown on the surface of silica and having sulfonic groups provide proton conductivity. [9] Highly-ordered silica colloidal crystals could serve as good inorganic matrix materials for DMFC proton conductive membranes, however they are limited by size, since it is challenging to obtain uniform and evenly thick free-standing membrane of large size (e.g. of one square inch). To avoid these drawbacks we prepared uniform silica nanoporous colloidal glass membrane by pressing silica spheres together using hydraulic press. In this work, we studied the dependence of proton conductivity of the polymer-modified sintered silica colloidal crystal on the degree of sulfonation of the polymer. The concentration of sulfonic groups was varied by copolymerizing of different ratios of 3-sulfopropylmethacrylate and 2-ethoxyethylmethacrylate (Figure 1) on the surface inside the nanopores of silica membranes. 2-Ethoxyethylmethacrylate was chosen as copolymerizing monomer because it does not contribute to proton conductivity due to its structure, at the same time it has approximately same size as the SPM, which is important for preventing any undesired steric
Data Loading...
