Sulfonated Poly(aryl ether ketone) on Side Chain/Sulfonated Poly(vinyl alcohol) Composite Proton Exchange Membrane for Direct Methanol Fuel Cells

Abstract

Poly(aryl ether ketone)/sulfated poly(vinyl alcohol) (S-SPAEK/SPVA) composite membranes with different mass fractions of SPVA were prepared by solution casting using highly sulfonated side-chain-type sulfonated poly(aryl ether ketone) and sulfated poly(vinyl alcohol) as raw materials. Fourier transform infrared (FTIR) spectroscopy confirmed the structure of the S-SPAEK/SPVA composite membranes. Scanning electron microscope (SEM) images showed that SPVA was uniformly dispersed in an S-SPAEK polymer matrix. The uptake and swelling behavior, water retention capacity, methanol permeability, and proton conductivity of the composite membrane were investigated systematically. The performance testing of the composite membranes revealed that thermal stability and water absorption and retention capabilities were improved by introduction of SPVA. The methanol permeability of S-SPAEK/SPVA composite membranes decreased as the content of SPVA increased because the hydroxyl groups could effectively obstruct diffusion of methanol molecules. The methanol diffusion coefficients of the composite membranes decreased from 7.9 x 10(-7) cm(2) . s(-1) for S-SPAEK/SPVA5 to 1.3 x 10(-7) cm(2) . s(-1) for S-SPAEK/SPVA30; considerably lower than 11.5x10(-7) cm(2) . s(-1) for the pure S- SPAEK membrane. The water absorption and retention capabilities increased as the numbers of hydrophilic groups increased by introduction of SPVA. As a result, the proton conductivity of the composite membranes increased with increasing water absorption and retention capabilities according to the Vehicle and Grotthuss mechanisms. The flexible chain segment of SPVA interacted strongly with the pendant chain of S-SPAEK, aiding hydrophilic/hydrophobic separation, and improving the proton conductivity of the composite membranes. The proton conductivity of the S- SPAEK/SPVA30 composite membrane reached 0.071 and 0.095 S . cm(-1) at 25 and 80 degrees C, respectively. These results show that S-SPAEK/SPVA composite membranes are promising for application in direct methanol fuel cells.