Introduction Solid alkaline fuel cell using anion exchange membrane (AEM) attracts increasing attention since non-noble metal electrode catalyst and high density liquid fuel can be used. However, development of chemically durable membrane is critical for long-term operation. AEM consisting of only aromatic component and anion exchange group such as polyphenylene AEM is potential candidate for highly durable membranes, but is suffered from low solubility due to the rigid linear backbone.
To overcome this problem, we have synthesized a spirobifluorene- based aromatic AEM as a highly soluble and durable AEM and used this AEM as an ionomer of methanol fuel cell.
Method Target AEM was synthesized by polymerization of the spirobifluorene and the phenyl monomers and successive quaternization. Alkaline and radical stability of this membrane were evaluated by comparing 1H-NMR spectra before and after soaking into 1M NaOH aq, and fentone solution. Finally, MEA was fabricated by using this AEM ionomer and direct Methanol fuel cell performance and durability were investigated at 80 oC.
Results and Discussion The synthesized membrane can be dissolved well into chloroform, tetrahydrofran and mixed solvent of THF and 1-propanol but not dissolved into fuel methanol.
1H-NMR spectra of this membrane did not change at all even after soaking into 1M NaOH aq. for one week indicating high alkaline stability. After soaking into fentone solution, the aromatic region of 1H-NMR did not change indicating high radical stability of the polymer backbone.
Direct methanol fuel cell using this membrane shows high and durable performances at 80 oC. These performances did not change even after one week operation indicating that highly durable solid alkaline fuel cell was realized by using the membrane (Fig 1).
