Triblock SEBS/DVB crosslinked and sulfonated membranes: Fuel cell performance and conductivity

Abstract

A set of styrene‐ethylene‐butylene‐styrene triblock copolymer (SEBS) membranes with 10 or 25 wt% divinyl‐benzene (DVB) as a crosslinking agent were prepared and validated. Physicochemical characterization revealed suitable hydrolytic and thermal stability of photo‐crosslinked membranes containing 25 wt% DVB and post‐sulfonated. These compositions were evaluated in H2/O2 single cells, and electrical and proton conductivities were furtherly assessed. The membranes with the milder post‐sulfonation showed greater proton conductivity than those with excessive sulfonation. In terms of electrical conductivity, a universal power law was applied, and the values obtained were low enough for being used as polyelectrolytes. At the analyzed temperatures, the charge transport process follows a long‐range pathway or vehicular model. Finally, fuel cell performance revealed the best behavior for the membrane with 25 wt% DVB, photo‐crosslinked during 30 min and mild sulfonated, with a promising power density of 526 mW·cm−2. Overall, the results obtained highlight the promising fuel cell performance of these cost‐effective triblock copolymer‐based membranes and indicate that higher sulfonation does not necessarily imply better power density.

High-Performance Proton Exchange Membrane of Sulfonated Polystyrene-b-polyisobutylene-b-polystyrene

“…The sulfonated or quaternized SEBS , and sulfonated, quaternized, or imidazolied SIBS ,− are regarded as the promising alternative for manufacturing PEMs or anionic exchange membranes (AEMs). The through-plane proton conductivity of the uncross-linked sulfonated SEBS (SSEBS) measured by the two-probe electrode method is about 0.5–45 mS·cm –1 at room temperature. − With the increase of the sulfonation degree, the through-plane proton conductivity of SSEBS could be increased to 45 mS·cm –1 ; however, the 100% water uptake of SSEBS results in poor mechanical properties and cannot be used in PEM. , The cross-linkage in SSEBS by introduction of a large amount (25%) of divinylbenzene (DVB) cross-linking agent could only decrease the water uptake from 185% to 95%, while the resulting cross-linked SSEBS/DVB composite membrane had a low through-plane proton conductivity of around 24 mS·cm –1 at room temperature and 100% of relative humility. ,, The power density of the uncross-linked SSEBS membrane used in DMFCs was measured to be 15 mW·cm –2 in the literature . On the other hand, it is recognized that there are inherent drawbacks of SSEBS as a PEM. ,, The poor oxidation stability of SSEBS was caused by the tertiary carbon of the butene structure in EB soft segments along the SSEBS macromolecular chains.…”

“…In particular, polystyrene-based triblock copolymer thermoplastic elastomers containing middle soft rubbery segments, such as polystyrene-b-poly(ethylene-co-butylene)-bpolystyrene (SEBS) and polystyrene-b-polyisobutylene-b-polystyrene (SIBS) block copolymers, exhibit phase separation micromorphology, effectively balancing the strength, brittleness, and elasticity of the materials. The sulfonated or quaternized SEBS 42,43 and sulfonated, quaternized, or imidazolied SIBS 27,44−50 are regarded as the promising alternative for manufacturing PEMs or anionic exchange membranes (AEMs). The through-plane proton conductivity of the uncross-linked sulfonated SEBS (SSEBS) measured by the two-probe electrode method is about 0.5−45 mS•cm −1 at room temperature.…”

“…53,54 The cross-linkage in SSEBS by introduction of a large amount (25%) of divinylbenzene (DVB) crosslinking agent could only decrease the water uptake from 185% to 95%, while the resulting cross-linked SSEBS/DVB composite membrane had a low through-plane proton conductivity of around 24 mS•cm −1 at room temperature and 100% of relative humility. 42,52,55 The power density of the uncross-linked SSEBS membrane used in DMFCs was measured to be 15 mW•cm −2 in the literature. 56 On the other hand, it is recognized that there are inherent drawbacks of SSEBS as a PEM.…”

“…In particular, polystyrene-based triblock copolymer thermoplastic elastomers containing middle soft rubbery segments, such as polystyrene- b -poly­(ethylene- co -butylene)- b -polystyrene (SEBS) and polystyrene- b -polyisobutylene- b -polystyrene (SIBS) block copolymers, exhibit phase separation micromorphology, effectively balancing the strength, brittleness, and elasticity of the materials. The sulfonated or quaternized SEBS , and sulfonated, quaternized, or imidazolied SIBS ,− are regarded as the promising alternative for manufacturing PEMs or anionic exchange membranes (AEMs). The through-plane proton conductivity of the uncross-linked sulfonated SEBS (SSEBS) measured by the two-probe electrode method is about 0.5–45 mS·cm –1 at room temperature. − With the increase of the sulfonation degree, the through-plane proton conductivity of SSEBS could be increased to 45 mS·cm –1 ; however, the 100% water uptake of SSEBS results in poor mechanical properties and cannot be used in PEM. , The cross-linkage in SSEBS by introduction of a large amount (25%) of divinylbenzene (DVB) cross-linking agent could only decrease the water uptake from 185% to 95%, while the resulting cross-linked SSEBS/DVB composite membrane had a low through-plane proton conductivity of around 24 mS·cm –1 at room temperature and 100% of relative humility. ,, The power density of the uncross-linked SSEBS membrane used in DMFCs was measured to be 15 mW·cm –2 in the literature .…”