Abstract
Hydrolytic stability and oxidative stability are the core properties of sulfonated polynaphthylimides (SPIs) as proton exchange membranes. The chemical structure of SPIs directly influences the performance. Herein, three different series of branched SPIs were designed and prepared using 1,3,5-tris (2-trifluoromethyl-4-aminophenoxy) benzene as a trifunctional monomer and three non-sulfonated diamine monomers, such as 4,4′-oxydianiline (ODA), 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (6FODA), and 4,4′-(9-fluorenylidene)dianiline (BFDA). The effect of the chemical structure and degree of branching on SPIs properties is discussed. The results showed that by controlling the chemical structure and degree of branching, the chemical stability of SPIs changed significantly. SPI-6FODA with two ether linkages and a hydrophobic CF3 group has higher hydrolytic stability than SPI-ODA with only one ether linkage. In addition, with the increase of the introduced B3 monomer, the oxidation stability of SPI-6FODA has been greatly improved. We successfully synthesized SPIs with a high hydrolytic stability and oxidative stability.
Highlights
Facing the depletion of oil resources and the increasing environmental pollution caused by fossil fuels, proton exchange membrane fuel cells (PEMFC) have been recognized as one of the clean energy devices in the future [1,2,3,4,5,6,7]
Three sulfonated polynaphthylimides (SPIs) series with a 66.7% degree of sulfonation and different branching degrees were synthesized by changing the ratio of different monomer additions
When SPIs proton exchange membranes are used in fuel cells, their chemical instability mainly comes from two aspects: (1) hydrolysis of imide rings under high humidity and high temperature conditions; (2) being attacked by peroxide and hydroxyl radicals, generated by crossover or bleeding air reacting with hydrogen in the anode [40]
Summary
Facing the depletion of oil resources and the increasing environmental pollution caused by fossil fuels, proton exchange membrane fuel cells (PEMFC) have been recognized as one of the clean energy devices in the future [1,2,3,4,5,6,7]. Three different non-sulfonated diamine monomers, such as 4,40 -oxydianiline (ODA) with one ether bond, 2,2- bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (6FODA) with two ether bonds and hydrophobic -CF3 , and 4,40 -(9-fluorenylidene)dianiline (BFDA) large steric hindrance and 1,3,5-tris (2-trifluoromethyl-4-aminophenoxy) benzene with ether bond and -CF3 group as a trifunctional monomer were selected to synthesize three series of branched SPIs with different degrees of branching. These three series of branched SPIs with different branching degree were fabricated as proton exchange membranes, and their corresponding properties were characterized. The effects of different non-sulfonated diamine monomers and introduced branched structures on the performance of SPIs as a proton exchange membrane were studied
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