Ecofriendly and Simplified Synthetic Route for Polysulfone-based Solid-State Alkaline Electrolyte Membrane

Abstract

Problem statement: Recently the alkaline system for fuel cell enhance their presence because of possibility of no-precious-metal catalyst and low over potential at cathode reaction. The anion exchange membrane for alkaline membrane fuel cell should be a key technology in order to achieve the practical performance as fuel cells. Alkaline anion exchange membranes of high ionic conductivities are made from polysulfone by adding a chloromethyl pendant group to the polysulfone, follow by reacting the chloromethyl group with amine to form quarternary ammonium pendant groups which act as the counter ion for hydroxide anion. Chloromethyl methyl ether, N,N-dimethylformamide and methanol are commonly used as agent for providing excellent conversions, but they are now considered to be carcinogenic. To avoid the use of such hazardous materials, in our work we used paraformaldehyde, chlorotrimethylsilane, N-methylpyrrolidone and ethanol as agent for providing conversion. Approach: Polysulfone (PS) was chloromethylated using chlorotrimethylsilane as a chloromethylation reagent, resulting in the formation of Chloromethylated Polysulfone (CMPS). CMPS was converted to a quaternized form using trimethylamine and precipitated into ethanol. The powder was dissolved in N-methylpyrrolidone, followed by aminated with a 25 wt% trimethylamine. Results: The resulting solution was cast onto a flat glass plate and dried in an oven. The membrane was immersed in KOH solution for 24 h to replace the Cl- anion in the polymer with OH^-. Conclusion: The swelling behavior of polysulfone-based solid-state alkaline electrolyte membrane was closely related to the degree of water uptake (25 WU%, 7.5 SD%) and the ion-exchange capacity was 1.05 mmol g^-1, which is sufficient for electrolyte membranes used in alkaline fuel cells.