Surface-Densified Non-Fluorinated Proton Exchange Membrane Used for Direct Methanol Fuel Cell

Abstract

Novel bifunctional polyhedral oligomeric silsesquioxane (Vi-POSS-SO3Na) and a surface densification method to fabricate the composite membrane based on sulfonated poly (fluorenyl etherketone) (SPFEK) is reported for application in direct methanol fuel cells (DMFCs). First, the synthetic Vi-POSS-SO3Na implants on the SPFEK surface by swelling-filling process. Then, the vinyl groups on POSS are cross-linked to form a dense X-POSS layer on the membrane surface by a simple thermal treatment called surface densification. The crosslinked dense X-POSS with sulfonated groups on the composite membrane surface can effectively prevent the permeation of methanol and enhance the oxidative stability without sacrificing proton conductivity. The SPFEK/POSS-0.09 membrane with an area loading of 0.09 mg cm-2 POSS exhibits enhanced oxidative stability and the lowest methanol permeability (2.12×10-8 cm2 s-1). A direct methanol fuel cell was assembled and its performance was evaluated. The peak power density using SPFEK/POSS-0.03 membrane reaches 65.1 mW cm-2 that is much higher than the one (24.8 mW cm-2) using pristine SPFEK membrane at 80°C. The results demonstrate that the surface densification is an effective method for suppressing methanol crossover and surface-densified SPFEK/POSS proton exchange membrane with X-POSS layer has improved the comprehensive performance of composite membrane.

Self-Healing Sulfonated Poly(ether ether ketone)-Based Polymer Electrolyte Membrane for Direct Methanol Fuel Cells: Effect of Solvent Content

“…To address the issue of methanol crossover, researchers have investigated various methods of modifying Nafion, such as blending with a low-methanol permeable polymer, incorporating inorganic particles, and coating with a layer that is impermeable to methanol [ 13 , 14 ]. Increasing interest has also been shown in the development of non-Nafion-based membranes to counteract the shortcomings of expensive Nafion [ 15 , 16 ]. Among all the developed alternatives, sulfonated poly(ether ether ketone) (SPEEK) is the most promising due to its adjustable proton conductivity and superior mechanical stability [ 17 , 18 , 19 , 20 , 21 ].…”