Investigation and Characterization of the Effects of PEEK Sulfonation Parameters on Proton Exchange Membrane Properties for Direct Methanol Fuel Cells

ABSTRACT This study investigates the synthesis and characterization of sulfonated polyether ether ketone (sPEEK) membranes for application in proton exchange membrane fuel cells (PEMFCs). Initially, polyether ether ketone (PEEK) was subjected to sulfonation to enhance proton conductivity. Membranes sulfonated at different PEEK/acid ratios (4%, 5%, 8%, 10%, and 12% wt) were obtained by solution casting method. The study aimed to examine the influence of sulfonation parameters on membrane properties and to elucidate the polymer's behavior in solution, through viscosity and molecular weight measurements. Molecular weight, ion exchange capacity, and degree of sulfonation were evaluated for all membranes. Comprehensive structural and electrochemical characterizations were performed. Direct methanol fuel cell (DMFC) tests at methanol concentration of 3 M and with a flow rate of 4 mol/min and at 80°C for Nafion212, sPEEK4, sPEEK8, and sPEEK12. Single cell tests generated the peak current and power densities of all MEA samples (62 mA cm −2 /27 mW cm −2 , 59 mA cm −2 /26 mW cm −2 , 48 mA cm −2 /21 mW cm −2 and 43 mA cm −2 /17 mW cm −2, respectively. Overall, this study highlights the potential of sPEEK membranes by combining high proton conductivity, excellent ion exchange capacity, mechanical strength, and thermal stability if the sulfonation parameters are controlled well.