title: Characterization of Polyethylene-Graft-Sulfonated Polyarylsulfone Proton Exchange Membranes for Direct Methanol Fuel Cell Applications.
abstract: This paper examines polymer film morphology and several important properties of polyethylene-graft-sulfonated polyarylene ether sulfone (PE-g-s-PAES) proton exchange membranes (PEMs) for direct methanol fuel cell applications. Due to the extreme surface energy differences between a semi-crystalline and hydrophobic PE backbone and several amorphous and hydrophilic s-PAES side chains, the PE-g-s-PAES membrane self-assembles into a unique morphology, with many proton conductive s-PAES channels embedded in the stable and tough PE matrix and a thin hydrophobic PE layer spontaneously formed on the membrane surfaces. In the bulk, these membranes show good mechanical properties (tensile strength >30 MPa, Young's modulus >1400 MPa) and low water swelling (λ < 15) even with high IEC >3 mmol/g in the s-PAES domains. On the surface, the thin hydrophobic and semi-crystalline PE layer shows some unusual barrier (protective) properties. In addition to exhibiting higher through-plane conductivity (up to 160 mS/cm) than in-plane conductivity, the PE surface layer minimizes methanol cross-over from anode to cathode with reduced fuel loss, and stops the HO• and HO₂• radicals, originally formed at the anode, entering into PEM matrix. Evidently, the thin PE surface layer provides a highly desirable protecting layer for PEMs to reduce fuel loss and increase chemical stability. Overall, the newly developed PE-g-s-PAES membranes offer a desirable set of PEM properties, including conductivity, selectivity, mechanical strength, stability, and cost-effectiveness for direct methanol fuel cell applications.
authors.affiliation: Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802, USA. tcc3@psu.edu.
authors.forename: Hyung Kyu
authors.initials: HK
authors.lastname: Kim
authors.affiliation: Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802, USA. guz6@psu.edu.
authors.forename: Gang
authors.initials: G
authors.lastname: Zhang
authors.affiliation: Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802, USA. cun120@psu.edu.
authors.forename: Changwoo
authors.initials: C
authors.lastname: Nam
authors.affiliation: Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802, USA. chung@ems.psu.edu.
authors.forename: T C Mike
authors.initials: TC
authors.lastname: Chung
keywords: direct methanol fuel cells; electrochemical stability; methanol permeability; polyethylene; surface hydrophobicity