Static and dynamic properties investigation of modified polyethersulfone membrane for direct methanol fuel cell applications

The present study's main focus is understanding the impact of modification, especially through phosphoric acid and acetic acid, on polyethersulfone (PES) membranes for direct methanol fuel cell application, as sulfonation is the preferred modification method. The cross-linking introduces the sulfonate, phosphonate, and carboxylate group in the polymer matrix, while the membrane's semi-crystalline nature and homogeneous surface are confirmed through instrumental analysis. The high ion exchange capacity and water retention capacity of the phosphoric acid cross-linked PES membrane (PPES-2) reveal its potentiality. The impact of different hydration levels and temperatures on proton conductivity indicates that based on the operating conditions, the cross-linked membrane can be used, such as at high temperatures and 50 % hydration level, the PPES-2 membrane shows high proton conductivity as well as has low methanol crossover due to the presence of hydroxyl group. At the same time, the acetic acid-treated PES (CPES-2) membrane shows high proton conductivity at 50 % hydration level and low temperature. The same is confirmed through molecular dynamic simulation by understanding their dynamic and static properties. The PPES-2 membrane shows maximum power density (0.34 Wcm- 2). In conclusion, the study indicates that PES modification can be done through phosphorylation and carboxylation, apart from sulfonation.