Synthesis of Polyethylene-Based Proton Exchange Membranes Containing PE Backbone and Sulfonated Poly(arylene ether sulfone) Side Chains for Fuel Cell Applications

Abstract

This paper discusses a new class of proton exchange membranes (PEMs) that are based on a wellcontrolled polyolefin graft copolymer containing a polyethylene (PE) backbone and several sulfonated poly(arylene ether sulfone) (s-PAES) side chains. The chemistry involves a graft-onto reaction between high molecular weight PE with few pendent benzyl bromide groups and poly(arylene ether sulfone) (PAES) with two terminal phenol groups. The resulting PE-g-PAES graft copolymer, with predetermined backbone molecular weight, graft density, and graft length, was solution-cast into uniform film (thickness 20−40 μm), followed by a heterogeneous sulfonation reaction of PAES side chains to obtain the desired PE-g-s-PAES PEMs with a high sulfonation level. The unique combination of hydrophobicity, semicrystallinity, and high molecular weight of the PE backbone offers PEM with a stable (nonswellable) matrix. The embedded hydrophilic s-PAES proton-conductive domains show only moderate water uptake, even with a high ion exchange capacity (IEC >3 mmol/g in the s-PAES domains). Compared to Nafion 117, most PE-g-s-PAES PEMs show similar hydration numbers (λ <15) but higher proton conductivity (up to 160 mS/cm). More interestingly, all PE-g-s-PAES PEMs show higher through-plane conductivity than in-plane conductivity. Evidently, a thin hydrophobic PE layer is formed on the PEM surfaces due to the low surface energy of PE, resulting in anisotropic conductivity. Overall, this newly developed PE-g-s-PAES membrane offers a combination of desirable properties, including conductivity, water uptake, mechanical strength, and cost-effectiveness for fuel cell applications.

Characterization of Polyethylene-Graft-Sulfonated Polyarylsulfone Proton Exchange Membranes for Direct Methanol Fuel Cell Applications

“…However, it is worthy to note that A-4 PEM abruptly increases methanol permeability, which may be due to the change of the s-PAES hydrophilic phase. Based on our previous report [ 23 ], the percolation threshold for the s-PAES domains in the PE-g-s-PAES PEM is at the IEC value ~1.4 mmol/g. In this study, the abrupt increase of methanol permeability appears at around IEC~1.6 mmol/g.…”

“…In our previous paper [ 23 ], we discussed the synthesis of a polyethylene- graft -sulfonated poly(arylene ether sulfone) (PE-g-s-PAES) graft copolymer that contains a semi-crystalline and hydrophobic PE backbone and several amorphous and hydrophilic s-PAES side chains, as illustrated in Scheme 1 . We examined some of its related PEMFC properties, including water swelling, ion exchange capacity, and proton conductivity.…”

Functionalization of Polypropylene by the Combination of Metallocene Catalysts and Reactive Comonomers

“…Most of them showed good interfacial activities and improved morphology in polyolefin blends and composites . Some specialty PP polymers are used for electric and energy applications . Furthermore, the reactive comonomer approach has also been extended to chain transfer agents that afford chain end functionalized polyolefins and polyolefin block copolymers …”

Effect of different ion-aggregating structures on the property of proton conducting membrane based on polyvinyl alcohol

“…These holes represent the hydrophilic domains containing water [35][36][37], which is benefit for the water uptake. The pendent-type side chain can drive the ionic clusters to aggregate and the hydration number will increase [38,39]. During the process of membrane preparation, the membranes were annealed at high temperature.…”